数据类型详解
一、数据类型概览
1.1 类型体系
<mxfile>
<diagram id="java-data-types" name="Java数据类型体系">
<mxGraphModel dx="1068" dy="484" grid="1" gridSize="10" guides="1" tooltips="1" connect="1" arrows="1" fold="1" page="1" pageScale="1" pageWidth="900" pageHeight="680" math="0" shadow="0">
<root>
<mxCell id="0" />
<mxCell id="1" parent="0" />
<mxCell id="2" parent="1" style="text;html=1;strokeColor=none;fillColor=none;align=center;verticalAlign=middle;fontSize=22;fontStyle=1;fontColor=#1E293B;" value="Java 数据类型体系" vertex="1">
<mxGeometry height="40" width="300" x="300" y="20" as="geometry" />
</mxCell>
<mxCell id="3" parent="1" style="rounded=1;whiteSpace=wrap;html=1;fillColor=#6366F1;strokeColor=#4F46E5;strokeWidth=2;fontSize=14;fontStyle=1;fontColor=#FFFFFF;" value="数据类型" vertex="1">
<mxGeometry height="44" width="140" x="380" y="70" as="geometry" />
</mxCell>
<mxCell id="4" edge="1" parent="1" source="3" style="edgeStyle=orthogonalEdgeStyle;rounded=0;orthogonalLoop=1;jettySize=auto;html=1;strokeColor=#64748B;strokeWidth=2;endArrow=none;endFill=0;" value="">
<mxGeometry relative="1" as="geometry">
<mxPoint x="450" y="140" as="targetPoint" />
</mxGeometry>
</mxCell>
<mxCell id="5" edge="1" parent="1" style="edgeStyle=orthogonalEdgeStyle;rounded=0;orthogonalLoop=1;jettySize=auto;html=1;strokeColor=#64748B;strokeWidth=2;endArrow=classic;endFill=1;" value="">
<mxGeometry relative="1" as="geometry">
<Array as="points">
<mxPoint x="230" y="140" />
</Array>
<mxPoint x="450" y="140" as="sourcePoint" />
<mxPoint x="230" y="170" as="targetPoint" />
</mxGeometry>
</mxCell>
<mxCell id="6" edge="1" parent="1" style="edgeStyle=orthogonalEdgeStyle;rounded=0;orthogonalLoop=1;jettySize=auto;html=1;strokeColor=#64748B;strokeWidth=2;endArrow=classic;endFill=1;" value="">
<mxGeometry relative="1" as="geometry">
<Array as="points">
<mxPoint x="670" y="140" />
</Array>
<mxPoint x="450" y="140" as="sourcePoint" />
<mxPoint x="670" y="170" as="targetPoint" />
</mxGeometry>
</mxCell>
<mxCell id="7" parent="1" style="rounded=1;whiteSpace=wrap;html=1;fillColor=#3B82F6;strokeColor=#2563EB;strokeWidth=2;fontSize=13;fontStyle=1;fontColor=#FFFFFF;" value="基本类型<br><font style="font-size: 10px;">(Primitive)</font>" vertex="1">
<mxGeometry height="50" width="150" x="155" y="170" as="geometry" />
</mxCell>
<mxCell id="8" parent="1" style="rounded=1;whiteSpace=wrap;html=1;fillColor=#22C55E;strokeColor=#16A34A;strokeWidth=2;fontSize=13;fontStyle=1;fontColor=#FFFFFF;" value="引用类型<br><font style="font-size: 10px;">(Reference)</font>" vertex="1">
<mxGeometry height="50" width="150" x="595" y="170" as="geometry" />
</mxCell>
<mxCell id="9" edge="1" parent="1" style="edgeStyle=orthogonalEdgeStyle;rounded=0;orthogonalLoop=1;jettySize=auto;html=1;strokeColor=#3B82F6;strokeWidth=2;endArrow=none;endFill=0;" value="">
<mxGeometry relative="1" as="geometry">
<mxPoint x="230" y="220" as="sourcePoint" />
<mxPoint x="230" y="250" as="targetPoint" />
</mxGeometry>
</mxCell>
<mxCell id="10" edge="1" parent="1" style="edgeStyle=orthogonalEdgeStyle;rounded=0;orthogonalLoop=1;jettySize=auto;html=1;strokeColor=#3B82F6;strokeWidth=2;endArrow=classic;endFill=1;" value="">
<mxGeometry relative="1" as="geometry">
<Array as="points">
<mxPoint x="90" y="250" />
</Array>
<mxPoint x="230" y="250" as="sourcePoint" />
<mxPoint x="90" y="280" as="targetPoint" />
</mxGeometry>
</mxCell>
<mxCell id="11" edge="1" parent="1" style="edgeStyle=orthogonalEdgeStyle;rounded=0;orthogonalLoop=1;jettySize=auto;html=1;strokeColor=#3B82F6;strokeWidth=2;endArrow=classic;endFill=1;" value="">
<mxGeometry relative="1" as="geometry">
<mxPoint x="230" y="250" as="sourcePoint" />
<mxPoint x="230" y="280" as="targetPoint" />
</mxGeometry>
</mxCell>
<mxCell id="12" edge="1" parent="1" style="edgeStyle=orthogonalEdgeStyle;rounded=0;orthogonalLoop=1;jettySize=auto;html=1;strokeColor=#3B82F6;strokeWidth=2;endArrow=classic;endFill=1;" value="">
<mxGeometry relative="1" as="geometry">
<Array as="points">
<mxPoint x="370" y="250" />
</Array>
<mxPoint x="230" y="250" as="sourcePoint" />
<mxPoint x="370" y="280" as="targetPoint" />
</mxGeometry>
</mxCell>
<mxCell id="13" parent="1" style="rounded=1;whiteSpace=wrap;html=1;fillColor=#DBEAFE;strokeColor=#3B82F6;strokeWidth=2;fontSize=12;fontStyle=1;fontColor=#1E40AF;" value="整数" vertex="1">
<mxGeometry height="30" width="100" x="40" y="280" as="geometry" />
</mxCell>
<mxCell id="14" parent="1" style="rounded=1;whiteSpace=wrap;html=1;fillColor=#DBEAFE;strokeColor=#3B82F6;strokeWidth=2;fontSize=12;fontStyle=1;fontColor=#1E40AF;" value="浮点" vertex="1">
<mxGeometry height="30" width="100" x="180" y="280" as="geometry" />
</mxCell>
<mxCell id="15" parent="1" style="rounded=1;whiteSpace=wrap;html=1;fillColor=#DBEAFE;strokeColor=#3B82F6;strokeWidth=2;fontSize=12;fontStyle=1;fontColor=#1E40AF;" value="其他" vertex="1">
<mxGeometry height="30" width="100" x="320" y="280" as="geometry" />
</mxCell>
<mxCell id="16" parent="1" style="rounded=1;whiteSpace=wrap;html=1;fillColor=#F1F5F9;strokeColor=#94A3B8;strokeWidth=1;fontSize=11;fontFamily=Courier New;fontColor=#475569;align=center;" value="byte<br>short<br>int<br>long" vertex="1">
<mxGeometry height="80" width="100" x="40" y="320" as="geometry" />
</mxCell>
<mxCell id="17" parent="1" style="rounded=1;whiteSpace=wrap;html=1;fillColor=#F1F5F9;strokeColor=#94A3B8;strokeWidth=1;fontSize=11;fontFamily=Courier New;fontColor=#475569;align=center;" value="float<br>double" vertex="1">
<mxGeometry height="80" width="100" x="180" y="320" as="geometry" />
</mxCell>
<mxCell id="18" parent="1" style="rounded=1;whiteSpace=wrap;html=1;fillColor=#F1F5F9;strokeColor=#94A3B8;strokeWidth=1;fontSize=11;fontFamily=Courier New;fontColor=#475569;align=center;" value="char<br>boolean" vertex="1">
<mxGeometry height="80" width="100" x="320" y="320" as="geometry" />
</mxCell>
<mxCell id="19" edge="1" parent="1" style="edgeStyle=orthogonalEdgeStyle;rounded=0;orthogonalLoop=1;jettySize=auto;html=1;strokeColor=#22C55E;strokeWidth=2;endArrow=none;endFill=0;" value="">
<mxGeometry relative="1" as="geometry">
<mxPoint x="670" y="220" as="sourcePoint" />
<mxPoint x="670" y="250" as="targetPoint" />
</mxGeometry>
</mxCell>
<mxCell id="20" edge="1" parent="1" style="edgeStyle=orthogonalEdgeStyle;rounded=0;orthogonalLoop=1;jettySize=auto;html=1;strokeColor=#22C55E;strokeWidth=2;endArrow=classic;endFill=1;" value="">
<mxGeometry relative="1" as="geometry">
<Array as="points">
<mxPoint x="530" y="250" />
</Array>
<mxPoint x="670" y="250" as="sourcePoint" />
<mxPoint x="530" y="280" as="targetPoint" />
</mxGeometry>
</mxCell>
<mxCell id="21" edge="1" parent="1" style="edgeStyle=orthogonalEdgeStyle;rounded=0;orthogonalLoop=1;jettySize=auto;html=1;strokeColor=#22C55E;strokeWidth=2;endArrow=classic;endFill=1;" value="">
<mxGeometry relative="1" as="geometry">
<mxPoint x="670" y="250" as="sourcePoint" />
<mxPoint x="670" y="280" as="targetPoint" />
</mxGeometry>
</mxCell>
<mxCell id="22" edge="1" parent="1" style="edgeStyle=orthogonalEdgeStyle;rounded=0;orthogonalLoop=1;jettySize=auto;html=1;strokeColor=#22C55E;strokeWidth=2;endArrow=classic;endFill=1;" value="">
<mxGeometry relative="1" as="geometry">
<Array as="points">
<mxPoint x="810" y="250" />
</Array>
<mxPoint x="670" y="250" as="sourcePoint" />
<mxPoint x="810" y="280" as="targetPoint" />
</mxGeometry>
</mxCell>
<mxCell id="23" parent="1" style="rounded=1;whiteSpace=wrap;html=1;fillColor=#DCFCE7;strokeColor=#22C55E;strokeWidth=2;fontSize=12;fontStyle=1;fontColor=#166534;" value="类<br><font style="font-size: 10px;">Class</font>" vertex="1">
<mxGeometry height="30" width="100" x="480" y="280" as="geometry" />
</mxCell>
<mxCell id="24" parent="1" style="rounded=1;whiteSpace=wrap;html=1;fillColor=#DCFCE7;strokeColor=#22C55E;strokeWidth=2;fontSize=12;fontStyle=1;fontColor=#166534;" value="接口<br><font style="font-size: 10px;">Interface</font>" vertex="1">
<mxGeometry height="30" width="100" x="620" y="280" as="geometry" />
</mxCell>
<mxCell id="25" parent="1" style="rounded=1;whiteSpace=wrap;html=1;fillColor=#DCFCE7;strokeColor=#22C55E;strokeWidth=2;fontSize=12;fontStyle=1;fontColor=#166534;" value="数组<br><font style="font-size: 10px;">Array</font>" vertex="1">
<mxGeometry height="30" width="100" x="760" y="280" as="geometry" />
</mxCell>
<mxCell id="26" parent="1" style="rounded=1;whiteSpace=wrap;html=1;fillColor=#F1F5F9;strokeColor=#94A3B8;strokeWidth=1;fontSize=11;fontFamily=Courier New;fontColor=#475569;align=center;" value="String<br>Object<br>..." vertex="1">
<mxGeometry height="80" width="100" x="480" y="320" as="geometry" />
</mxCell>
<mxCell id="27" parent="1" style="rounded=1;whiteSpace=wrap;html=1;fillColor=#F1F5F9;strokeColor=#94A3B8;strokeWidth=1;fontSize=11;fontFamily=Courier New;fontColor=#475569;align=center;" value="List<br>Map<br>..." vertex="1">
<mxGeometry height="80" width="100" x="620" y="320" as="geometry" />
</mxCell>
<mxCell id="28" parent="1" style="rounded=1;whiteSpace=wrap;html=1;fillColor=#F1F5F9;strokeColor=#94A3B8;strokeWidth=1;fontSize=11;fontFamily=Courier New;fontColor=#475569;align=center;" value="int[]<br>String[]<br>..." vertex="1">
<mxGeometry height="80" width="100" x="760" y="320" as="geometry" />
</mxCell>
<mxCell id="29" parent="1" style="rounded=1;whiteSpace=wrap;html=1;fillColor=#EFF6FF;strokeColor=#3B82F6;strokeWidth=2;dashed=1;" value="" vertex="1">
<mxGeometry height="70" width="380" x="40" y="430" as="geometry" />
</mxCell>
<mxCell id="30" parent="1" style="text;html=1;strokeColor=none;fillColor=none;align=left;verticalAlign=middle;fontSize=12;fontColor=#1E40AF;spacingLeft=8;" value="<b>基本类型</b>：8 种，直接存储值，效率高" vertex="1">
<mxGeometry height="40" width="360" x="50" y="445" as="geometry" />
</mxCell>
<mxCell id="31" parent="1" style="rounded=1;whiteSpace=wrap;html=1;fillColor=#F0FDF4;strokeColor=#22C55E;strokeWidth=2;dashed=1;" value="" vertex="1">
<mxGeometry height="70" width="420" x="460" y="430" as="geometry" />
</mxCell>
<mxCell id="32" parent="1" style="text;html=1;strokeColor=none;fillColor=none;align=left;verticalAlign=middle;fontSize=12;fontColor=#166534;spacingLeft=8;" value="<b>引用类型</b>：存储对象的内存地址（引用），指向堆中的对象" vertex="1">
<mxGeometry height="40" width="400" x="470" y="445" as="geometry" />
</mxCell>
<mxCell id="33" parent="1" style="ellipse;whiteSpace=wrap;html=1;fillColor=#3B82F6;strokeColor=#2563EB;strokeWidth=1;fontSize=10;fontStyle=1;fontColor=#FFFFFF;" value="8种" vertex="1">
<mxGeometry height="20" width="30" x="305" y="185" as="geometry" />
</mxCell>
<mxCell id="34" parent="1" style="ellipse;whiteSpace=wrap;html=1;fillColor=#22C55E;strokeColor=#16A34A;strokeWidth=1;fontSize=10;fontStyle=1;fontColor=#FFFFFF;" value="∞" vertex="1">
<mxGeometry height="25" width="30" x="745" y="185" as="geometry" />
</mxCell>
</root>
</mxGraphModel>
</diagram>
</mxfile>
1.2 基本类型一览表
<mxfile>
<diagram id="java-primitive-types" name="8种基本数据类型">
<mxGraphModel dx="1068" dy="484" grid="1" gridSize="10" guides="1" tooltips="1" connect="1" arrows="1" fold="1" page="1" pageScale="1" pageWidth="900" pageHeight="750" math="0" shadow="0">
<root>
<mxCell id="0" />
<mxCell id="1" parent="0" />
<mxCell id="2" parent="1" style="text;html=1;strokeColor=none;fillColor=none;align=center;verticalAlign=middle;fontSize=22;fontStyle=1;fontColor=#1E293B;" value="8 种基本数据类型" vertex="1">
<mxGeometry height="40" width="300" x="300" y="20" as="geometry" />
</mxCell>
<mxCell id="3" parent="1" style="rounded=0;whiteSpace=wrap;html=1;fillColor=#6366F1;strokeColor=#4F46E5;strokeWidth=2;fontSize=13;fontStyle=1;fontColor=#FFFFFF;" value="类型" vertex="1">
<mxGeometry height="40" width="100" x="40" y="70" as="geometry" />
</mxCell>
<mxCell id="4" parent="1" style="rounded=0;whiteSpace=wrap;html=1;fillColor=#6366F1;strokeColor=#4F46E5;strokeWidth=2;fontSize=13;fontStyle=1;fontColor=#FFFFFF;" value="字节" vertex="1">
<mxGeometry height="40" width="60" x="140" y="70" as="geometry" />
</mxCell>
<mxCell id="5" parent="1" style="rounded=0;whiteSpace=wrap;html=1;fillColor=#6366F1;strokeColor=#4F46E5;strokeWidth=2;fontSize=13;fontStyle=1;fontColor=#FFFFFF;" value="位" vertex="1">
<mxGeometry height="40" width="50" x="200" y="70" as="geometry" />
</mxCell>
<mxCell id="6" parent="1" style="rounded=0;whiteSpace=wrap;html=1;fillColor=#6366F1;strokeColor=#4F46E5;strokeWidth=2;fontSize=13;fontStyle=1;fontColor=#FFFFFF;" value="默认值" vertex="1">
<mxGeometry height="40" width="90" x="250" y="70" as="geometry" />
</mxCell>
<mxCell id="7" parent="1" style="rounded=0;whiteSpace=wrap;html=1;fillColor=#6366F1;strokeColor=#4F46E5;strokeWidth=2;fontSize=13;fontStyle=1;fontColor=#FFFFFF;" value="取值范围" vertex="1">
<mxGeometry height="40" width="520" x="340" y="70" as="geometry" />
</mxCell>
<mxCell id="8" parent="1" style="rounded=0;whiteSpace=wrap;html=1;fillColor=#DBEAFE;strokeColor=#93C5FD;strokeWidth=1;fontSize=12;fontStyle=1;fontFamily=Courier New;fontColor=#1E40AF;" value="byte" vertex="1">
<mxGeometry height="60" width="100" x="40" y="120" as="geometry" />
</mxCell>
<mxCell id="9" parent="1" style="rounded=0;whiteSpace=wrap;html=1;fillColor=#F1F5F9;strokeColor=#CBD5E1;strokeWidth=1;fontSize=12;fontColor=#334155;" value="1" vertex="1">
<mxGeometry height="60" width="60" x="140" y="120" as="geometry" />
</mxCell>
<mxCell id="10" parent="1" style="rounded=0;whiteSpace=wrap;html=1;fillColor=#F1F5F9;strokeColor=#CBD5E1;strokeWidth=1;fontSize=12;fontColor=#334155;" value="8" vertex="1">
<mxGeometry height="60" width="50" x="200" y="120" as="geometry" />
</mxCell>
<mxCell id="11" parent="1" style="rounded=0;whiteSpace=wrap;html=1;fillColor=#F1F5F9;strokeColor=#CBD5E1;strokeWidth=1;fontSize=12;fontFamily=Courier New;fontColor=#334155;" value="0" vertex="1">
<mxGeometry height="60" width="90" x="250" y="120" as="geometry" />
</mxCell>
<mxCell id="12" parent="1" style="rounded=0;whiteSpace=wrap;html=1;fillColor=#F1F5F9;strokeColor=#CBD5E1;strokeWidth=1;fontSize=12;fontColor=#334155;align=center;" value="-128 ~ 127<br><font style="font-size: 10px;" color="#64748b">(-2⁷ ~ 2⁷-1)</font>" vertex="1">
<mxGeometry height="60" width="520" x="340" y="120" as="geometry" />
</mxCell>
<mxCell id="13" parent="1" style="rounded=0;whiteSpace=wrap;html=1;fillColor=#DBEAFE;strokeColor=#93C5FD;strokeWidth=1;fontSize=12;fontStyle=1;fontFamily=Courier New;fontColor=#1E40AF;" value="short" vertex="1">
<mxGeometry height="60" width="100" x="40" y="180" as="geometry" />
</mxCell>
<mxCell id="14" parent="1" style="rounded=0;whiteSpace=wrap;html=1;fillColor=#EFF6FF;strokeColor=#CBD5E1;strokeWidth=1;fontSize=12;fontColor=#334155;" value="2" vertex="1">
<mxGeometry height="60" width="60" x="140" y="180" as="geometry" />
</mxCell>
<mxCell id="15" parent="1" style="rounded=0;whiteSpace=wrap;html=1;fillColor=#EFF6FF;strokeColor=#CBD5E1;strokeWidth=1;fontSize=12;fontColor=#334155;" value="16" vertex="1">
<mxGeometry height="60" width="50" x="200" y="180" as="geometry" />
</mxCell>
<mxCell id="16" parent="1" style="rounded=0;whiteSpace=wrap;html=1;fillColor=#EFF6FF;strokeColor=#CBD5E1;strokeWidth=1;fontSize=12;fontFamily=Courier New;fontColor=#334155;" value="0" vertex="1">
<mxGeometry height="60" width="90" x="250" y="180" as="geometry" />
</mxCell>
<mxCell id="17" parent="1" style="rounded=0;whiteSpace=wrap;html=1;fillColor=#EFF6FF;strokeColor=#CBD5E1;strokeWidth=1;fontSize=12;fontColor=#334155;align=center;" value="-32768 ~ 32767<br><font style="font-size: 10px;" color="#64748b">(-2¹⁵ ~ 2¹⁵-1)</font>" vertex="1">
<mxGeometry height="60" width="520" x="340" y="180" as="geometry" />
</mxCell>
<mxCell id="18" parent="1" style="rounded=0;whiteSpace=wrap;html=1;fillColor=#DBEAFE;strokeColor=#93C5FD;strokeWidth=1;fontSize=12;fontStyle=1;fontFamily=Courier New;fontColor=#1E40AF;" value="int" vertex="1">
<mxGeometry height="60" width="100" x="40" y="240" as="geometry" />
</mxCell>
<mxCell id="19" parent="1" style="rounded=0;whiteSpace=wrap;html=1;fillColor=#F1F5F9;strokeColor=#CBD5E1;strokeWidth=1;fontSize=12;fontColor=#334155;" value="4" vertex="1">
<mxGeometry height="60" width="60" x="140" y="240" as="geometry" />
</mxCell>
<mxCell id="20" parent="1" style="rounded=0;whiteSpace=wrap;html=1;fillColor=#F1F5F9;strokeColor=#CBD5E1;strokeWidth=1;fontSize=12;fontColor=#334155;" value="32" vertex="1">
<mxGeometry height="60" width="50" x="200" y="240" as="geometry" />
</mxCell>
<mxCell id="21" parent="1" style="rounded=0;whiteSpace=wrap;html=1;fillColor=#F1F5F9;strokeColor=#CBD5E1;strokeWidth=1;fontSize=12;fontFamily=Courier New;fontColor=#334155;" value="0" vertex="1">
<mxGeometry height="60" width="90" x="250" y="240" as="geometry" />
</mxCell>
<mxCell id="22" parent="1" style="rounded=0;whiteSpace=wrap;html=1;fillColor=#F1F5F9;strokeColor=#CBD5E1;strokeWidth=1;fontSize=12;fontColor=#334155;align=center;" value="-2147483648 ~ 2147483647<br><font style="font-size: 10px;" color="#64748b">(-2³¹ ~ 2³¹-1)</font>" vertex="1">
<mxGeometry height="60" width="520" x="340" y="240" as="geometry" />
</mxCell>
<mxCell id="23" parent="1" style="rounded=0;whiteSpace=wrap;html=1;fillColor=#DBEAFE;strokeColor=#93C5FD;strokeWidth=1;fontSize=12;fontStyle=1;fontFamily=Courier New;fontColor=#1E40AF;" value="long" vertex="1">
<mxGeometry height="60" width="100" x="40" y="300" as="geometry" />
</mxCell>
<mxCell id="24" parent="1" style="rounded=0;whiteSpace=wrap;html=1;fillColor=#EFF6FF;strokeColor=#CBD5E1;strokeWidth=1;fontSize=12;fontColor=#334155;" value="8" vertex="1">
<mxGeometry height="60" width="60" x="140" y="300" as="geometry" />
</mxCell>
<mxCell id="25" parent="1" style="rounded=0;whiteSpace=wrap;html=1;fillColor=#EFF6FF;strokeColor=#CBD5E1;strokeWidth=1;fontSize=12;fontColor=#334155;" value="64" vertex="1">
<mxGeometry height="60" width="50" x="200" y="300" as="geometry" />
</mxCell>
<mxCell id="26" parent="1" style="rounded=0;whiteSpace=wrap;html=1;fillColor=#EFF6FF;strokeColor=#CBD5E1;strokeWidth=1;fontSize=12;fontFamily=Courier New;fontColor=#334155;" value="0L" vertex="1">
<mxGeometry height="60" width="90" x="250" y="300" as="geometry" />
</mxCell>
<mxCell id="27" parent="1" style="rounded=0;whiteSpace=wrap;html=1;fillColor=#EFF6FF;strokeColor=#CBD5E1;strokeWidth=1;fontSize=12;fontColor=#334155;align=center;" value="-2⁶³ ~ 2⁶³-1<br><font style="font-size: 10px;" color="#64748b">(约 ±922亿亿)</font>" vertex="1">
<mxGeometry height="60" width="520" x="340" y="300" as="geometry" />
</mxCell>
<mxCell id="28" parent="1" style="rounded=0;whiteSpace=wrap;html=1;fillColor=#FEF3C7;strokeColor=#FCD34D;strokeWidth=1;fontSize=12;fontStyle=1;fontFamily=Courier New;fontColor=#92400E;" value="float" vertex="1">
<mxGeometry height="60" width="100" x="40" y="360" as="geometry" />
</mxCell>
<mxCell id="29" parent="1" style="rounded=0;whiteSpace=wrap;html=1;fillColor=#FFFBEB;strokeColor=#FDE68A;strokeWidth=1;fontSize=12;fontColor=#334155;" value="4" vertex="1">
<mxGeometry height="60" width="60" x="140" y="360" as="geometry" />
</mxCell>
<mxCell id="30" parent="1" style="rounded=0;whiteSpace=wrap;html=1;fillColor=#FFFBEB;strokeColor=#FDE68A;strokeWidth=1;fontSize=12;fontColor=#334155;" value="32" vertex="1">
<mxGeometry height="60" width="50" x="200" y="360" as="geometry" />
</mxCell>
<mxCell id="31" parent="1" style="rounded=0;whiteSpace=wrap;html=1;fillColor=#FFFBEB;strokeColor=#FDE68A;strokeWidth=1;fontSize=12;fontFamily=Courier New;fontColor=#334155;" value="0.0f" vertex="1">
<mxGeometry height="60" width="90" x="250" y="360" as="geometry" />
</mxCell>
<mxCell id="32" parent="1" style="rounded=0;whiteSpace=wrap;html=1;fillColor=#FFFBEB;strokeColor=#FDE68A;strokeWidth=1;fontSize=12;fontColor=#334155;align=center;" value="±1.4E-45 ~ ±3.4E38<br><font style="font-size: 10px;" color="#64748b">(约 7 位有效数字)</font>" vertex="1">
<mxGeometry height="60" width="520" x="340" y="360" as="geometry" />
</mxCell>
<mxCell id="33" parent="1" style="rounded=0;whiteSpace=wrap;html=1;fillColor=#FEF3C7;strokeColor=#FCD34D;strokeWidth=1;fontSize=12;fontStyle=1;fontFamily=Courier New;fontColor=#92400E;" value="double" vertex="1">
<mxGeometry height="60" width="100" x="40" y="420" as="geometry" />
</mxCell>
<mxCell id="34" parent="1" style="rounded=0;whiteSpace=wrap;html=1;fillColor=#FEF9C3;strokeColor=#FDE68A;strokeWidth=1;fontSize=12;fontColor=#334155;" value="8" vertex="1">
<mxGeometry height="60" width="60" x="140" y="420" as="geometry" />
</mxCell>
<mxCell id="35" parent="1" style="rounded=0;whiteSpace=wrap;html=1;fillColor=#FEF9C3;strokeColor=#FDE68A;strokeWidth=1;fontSize=12;fontColor=#334155;" value="64" vertex="1">
<mxGeometry height="60" width="50" x="200" y="420" as="geometry" />
</mxCell>
<mxCell id="36" parent="1" style="rounded=0;whiteSpace=wrap;html=1;fillColor=#FEF9C3;strokeColor=#FDE68A;strokeWidth=1;fontSize=12;fontFamily=Courier New;fontColor=#334155;" value="0.0d" vertex="1">
<mxGeometry height="60" width="90" x="250" y="420" as="geometry" />
</mxCell>
<mxCell id="37" parent="1" style="rounded=0;whiteSpace=wrap;html=1;fillColor=#FEF9C3;strokeColor=#FDE68A;strokeWidth=1;fontSize=12;fontColor=#334155;align=center;" value="±4.9E-324 ~ ±1.8E308<br><font style="font-size: 10px;" color="#64748b">(约 15 位有效数字)</font>" vertex="1">
<mxGeometry height="60" width="520" x="340" y="420" as="geometry" />
</mxCell>
<mxCell id="38" parent="1" style="rounded=0;whiteSpace=wrap;html=1;fillColor=#DCFCE7;strokeColor=#86EFAC;strokeWidth=1;fontSize=12;fontStyle=1;fontFamily=Courier New;fontColor=#166534;" value="char" vertex="1">
<mxGeometry height="60" width="100" x="40" y="480" as="geometry" />
</mxCell>
<mxCell id="39" parent="1" style="rounded=0;whiteSpace=wrap;html=1;fillColor=#F0FDF4;strokeColor=#BBF7D0;strokeWidth=1;fontSize=12;fontColor=#334155;" value="2" vertex="1">
<mxGeometry height="60" width="60" x="140" y="480" as="geometry" />
</mxCell>
<mxCell id="40" parent="1" style="rounded=0;whiteSpace=wrap;html=1;fillColor=#F0FDF4;strokeColor=#BBF7D0;strokeWidth=1;fontSize=12;fontColor=#334155;" value="16" vertex="1">
<mxGeometry height="60" width="50" x="200" y="480" as="geometry" />
</mxCell>
<mxCell id="41" parent="1" style="rounded=0;whiteSpace=wrap;html=1;fillColor=#F0FDF4;strokeColor=#BBF7D0;strokeWidth=1;fontSize=11;fontFamily=Courier New;fontColor=#334155;" value="'\u0000'" vertex="1">
<mxGeometry height="60" width="90" x="250" y="480" as="geometry" />
</mxCell>
<mxCell id="42" parent="1" style="rounded=0;whiteSpace=wrap;html=1;fillColor=#F0FDF4;strokeColor=#BBF7D0;strokeWidth=1;fontSize=12;fontColor=#334155;align=center;" value="0 ~ 65535<br><font style="font-size: 10px;" color="#64748b">(Unicode 字符)</font>" vertex="1">
<mxGeometry height="60" width="520" x="340" y="480" as="geometry" />
</mxCell>
<mxCell id="43" parent="1" style="rounded=0;whiteSpace=wrap;html=1;fillColor=#FCE7F3;strokeColor=#F9A8D4;strokeWidth=1;fontSize=12;fontStyle=1;fontFamily=Courier New;fontColor=#9D174D;" value="boolean" vertex="1">
<mxGeometry height="60" width="100" x="40" y="540" as="geometry" />
</mxCell>
<mxCell id="44" parent="1" style="rounded=0;whiteSpace=wrap;html=1;fillColor=#FDF2F8;strokeColor=#FBCFE8;strokeWidth=1;fontSize=12;fontColor=#334155;" value="1*" vertex="1">
<mxGeometry height="60" width="60" x="140" y="540" as="geometry" />
</mxCell>
<mxCell id="45" parent="1" style="rounded=0;whiteSpace=wrap;html=1;fillColor=#FDF2F8;strokeColor=#FBCFE8;strokeWidth=1;fontSize=12;fontColor=#334155;" value="-" vertex="1">
<mxGeometry height="60" width="50" x="200" y="540" as="geometry" />
</mxCell>
<mxCell id="46" parent="1" style="rounded=0;whiteSpace=wrap;html=1;fillColor=#FDF2F8;strokeColor=#FBCFE8;strokeWidth=1;fontSize=12;fontFamily=Courier New;fontColor=#334155;" value="false" vertex="1">
<mxGeometry height="60" width="90" x="250" y="540" as="geometry" />
</mxCell>
<mxCell id="47" parent="1" style="rounded=0;whiteSpace=wrap;html=1;fillColor=#FDF2F8;strokeColor=#FBCFE8;strokeWidth=1;fontSize=12;fontColor=#334155;align=center;" value="true / false<br><font style="font-size: 10px;" color="#64748b">(*JVM 规范未明确定义)</font>" vertex="1">
<mxGeometry height="60" width="520" x="340" y="540" as="geometry" />
</mxCell>
<mxCell id="48" parent="1" style="text;html=1;strokeColor=none;fillColor=#3B82F6;align=center;verticalAlign=middle;fontSize=10;fontStyle=1;fontColor=#FFFFFF;rounded=1;" value="整数类型" vertex="1">
<mxGeometry height="16" width="50" x="40" y="120" as="geometry" />
</mxCell>
<mxCell id="49" parent="1" style="text;html=1;strokeColor=none;fillColor=#F59E0B;align=center;verticalAlign=middle;fontSize=10;fontStyle=1;fontColor=#FFFFFF;rounded=1;" value="浮点类型" vertex="1">
<mxGeometry height="16" width="50" x="40" y="360" as="geometry" />
</mxCell>
<mxCell id="50" parent="1" style="text;html=1;strokeColor=none;fillColor=#22C55E;align=center;verticalAlign=middle;fontSize=10;fontStyle=1;fontColor=#FFFFFF;rounded=1;" value="字符类型" vertex="1">
<mxGeometry height="16" width="50" x="40" y="480" as="geometry" />
</mxCell>
<mxCell id="51" parent="1" style="text;html=1;strokeColor=none;fillColor=#EC4899;align=center;verticalAlign=middle;fontSize=10;fontStyle=1;fontColor=#FFFFFF;rounded=1;" value="布尔类型" vertex="1">
<mxGeometry height="16" width="50" x="40" y="540" as="geometry" />
</mxCell>
<mxCell id="52" parent="1" style="rounded=1;whiteSpace=wrap;html=1;fillColor=none;strokeColor=#6366F1;strokeWidth=3;dashed=0;" value="" vertex="1">
<mxGeometry height="240" width="820" x="40" y="120" as="geometry" />
</mxCell>
<mxCell id="53" parent="1" style="rounded=1;whiteSpace=wrap;html=1;fillColor=none;strokeColor=#F59E0B;strokeWidth=3;dashed=0;" value="" vertex="1">
<mxGeometry height="120" width="820" x="40" y="360" as="geometry" />
</mxCell>
<mxCell id="54" parent="1" style="rounded=0;whiteSpace=wrap;html=1;fillColor=none;strokeColor=#64748B;strokeWidth=2;" value="" vertex="1">
<mxGeometry height="555" width="880" x="10" y="55" as="geometry" />
</mxCell>
<mxCell id="55" parent="1" style="text;html=1;strokeColor=none;fillColor=#F1F5F9;align=center;verticalAlign=middle;fontSize=12;fontColor=#475569;rounded=1;spacingLeft=8;spacingRight=8;" value="💡 记忆技巧：1-2-4-8 字节递增，整数默认 int，浮点默认 double" vertex="1">
<mxGeometry height="30" width="540" x="180" y="620" as="geometry" />
</mxCell>
</root>
</mxGraphModel>
</diagram>
</mxfile>
二、整数类型详解
2.1 取值范围的本质
<mxfile>
<diagram id="byte-range-explanation" name="为什么byte的范围是-128~127">
<mxGraphModel dx="1111" dy="980" grid="1" gridSize="10" guides="1" tooltips="1" connect="1" arrows="1" fold="1" page="1" pageScale="1" pageWidth="900" pageHeight="700" math="0" shadow="0">
<root>
<mxCell id="0" />
<mxCell id="1" parent="0" />
<mxCell id="2" parent="1" style="text;html=1;strokeColor=none;fillColor=none;align=center;verticalAlign=middle;whiteSpace=wrap;rounded=0;fontSize=20;fontStyle=1;fontColor=#1a1a2e;" value="为什么 byte 的范围是 -128 ~ 127？" vertex="1">
<mxGeometry height="40" width="600" x="150" y="20" as="geometry" />
</mxCell>
<mxCell id="3" parent="1" style="text;html=1;strokeColor=none;fillColor=none;align=center;verticalAlign=middle;whiteSpace=wrap;rounded=0;fontSize=14;fontColor=#666666;" value="计算机使用补码表示有符号整数" vertex="1">
<mxGeometry height="30" width="400" x="250" y="60" as="geometry" />
</mxCell>
<mxCell id="4" parent="1" style="rounded=1;whiteSpace=wrap;html=1;fillColor=#e1f5fe;strokeColor=#0288d1;strokeWidth=2;" value="" vertex="1">
<mxGeometry height="80" width="260" x="160" y="100" as="geometry" />
</mxCell>
<mxCell id="5" parent="1" style="text;html=1;strokeColor=none;fillColor=none;align=center;verticalAlign=middle;whiteSpace=wrap;rounded=0;fontSize=13;" value="<b>byte 占 8 位</b><br>最高位是符号位<br><font color="#0288d1">0 = 正数 &nbsp;│&nbsp; 1 = 负数</font>" vertex="1">
<mxGeometry height="80" width="260" x="160" y="100" as="geometry" />
</mxCell>
<mxCell id="6" parent="1" style="rounded=0;whiteSpace=wrap;html=1;fillColor=#ffcdd2;strokeColor=#c62828;strokeWidth=2;" value="" vertex="1">
<mxGeometry height="60" width="40" x="450" y="110" as="geometry" />
</mxCell>
<mxCell id="7" parent="1" style="text;html=1;strokeColor=none;fillColor=none;align=center;verticalAlign=middle;whiteSpace=wrap;rounded=0;fontSize=10;fontColor=#c62828;" value="符号位" vertex="1">
<mxGeometry height="20" width="60" x="440" y="170" as="geometry" />
</mxCell>
<mxCell id="8" parent="1" style="rounded=0;whiteSpace=wrap;html=1;fillColor=#c8e6c9;strokeColor=#388e3c;strokeWidth=2;" value="" vertex="1">
<mxGeometry height="60" width="245" x="495" y="110" as="geometry" />
</mxCell>
<mxCell id="9" parent="1" style="text;html=1;strokeColor=none;fillColor=none;align=center;verticalAlign=middle;whiteSpace=wrap;rounded=0;fontSize=10;fontColor=#388e3c;" value="数值位 (7位)" vertex="1">
<mxGeometry height="20" width="100" x="570" y="170" as="geometry" />
</mxCell>
<mxCell id="10" parent="1" style="text;html=1;strokeColor=none;fillColor=none;align=center;verticalAlign=middle;fontSize=9;fontColor=#999999;" value="bit7" vertex="1">
<mxGeometry height="20" width="40" x="450" y="90" as="geometry" />
</mxCell>
<mxCell id="11" parent="1" style="text;html=1;strokeColor=none;fillColor=none;align=center;verticalAlign=middle;fontSize=9;fontColor=#999999;" value="bit6 ~ bit0" vertex="1">
<mxGeometry height="20" width="100" x="570" y="90" as="geometry" />
</mxCell>
<mxCell id="12" parent="1" style="rounded=1;whiteSpace=wrap;html=1;fillColor=#fff3e0;strokeColor=#ff9800;strokeWidth=2;" value="" vertex="1">
<mxGeometry height="340" width="380" x="50" y="210" as="geometry" />
</mxCell>
<mxCell id="13" parent="1" style="text;html=1;strokeColor=none;fillColor=none;align=center;verticalAlign=middle;whiteSpace=wrap;rounded=0;fontSize=14;fontStyle=1;fontColor=#e65100;" value="二进制补码 → 十进制值" vertex="1">
<mxGeometry height="30" width="380" x="50" y="220" as="geometry" />
</mxCell>
<mxCell id="14" parent="1" style="rounded=0;whiteSpace=wrap;html=1;fillColor=#e8f5e9;strokeColor=#81c784;" value="" vertex="1">
<mxGeometry height="120" width="340" x="70" y="260" as="geometry" />
</mxCell>
<mxCell id="15" parent="1" style="text;html=1;strokeColor=none;fillColor=none;align=left;verticalAlign=middle;fontSize=12;" value="<font face="Courier New">0111 1111</font> → <b>+127</b> (最大正数)" vertex="1">
<mxGeometry height="25" width="300" x="90" y="265" as="geometry" />
</mxCell>
<mxCell id="16" parent="1" style="text;html=1;strokeColor=none;fillColor=none;align=left;verticalAlign=middle;fontSize=12;" value="<font face="Courier New">0111 1110</font> → <b>+126</b>" vertex="1">
<mxGeometry height="25" width="300" x="90" y="290" as="geometry" />
</mxCell>
<mxCell id="17" parent="1" style="text;html=1;strokeColor=none;fillColor=none;align=center;verticalAlign=middle;fontSize=14;fontColor=#666666;" value="..." vertex="1">
<mxGeometry height="20" width="300" x="90" y="310" as="geometry" />
</mxCell>
<mxCell id="18" parent="1" style="text;html=1;strokeColor=none;fillColor=none;align=left;verticalAlign=middle;fontSize=12;" value="<font face="Courier New">0000 0001</font> → <b>+1</b>" vertex="1">
<mxGeometry height="25" width="300" x="90" y="330" as="geometry" />
</mxCell>
<mxCell id="19" parent="1" style="text;html=1;strokeColor=none;fillColor=none;align=left;verticalAlign=middle;fontSize=12;" value="<font face="Courier New">0000 0000</font> → <b> 0</b>" vertex="1">
<mxGeometry height="25" width="300" x="90" y="355" as="geometry" />
</mxCell>
<mxCell id="20" parent="1" style="rounded=0;whiteSpace=wrap;html=1;fillColor=#ffebee;strokeColor=#e57373;" value="" vertex="1">
<mxGeometry height="145" width="340" x="70" y="390" as="geometry" />
</mxCell>
<mxCell id="21" parent="1" style="text;html=1;strokeColor=none;fillColor=none;align=left;verticalAlign=middle;fontSize=12;" value="<font face="Courier New">1111 1111</font> → <b>-1</b>" vertex="1">
<mxGeometry height="25" width="300" x="90" y="395" as="geometry" />
</mxCell>
<mxCell id="22" parent="1" style="text;html=1;strokeColor=none;fillColor=none;align=left;verticalAlign=middle;fontSize=12;" value="<font face="Courier New">1111 1110</font> → <b>-2</b>" vertex="1">
<mxGeometry height="25" width="300" x="90" y="420" as="geometry" />
</mxCell>
<mxCell id="23" parent="1" style="text;html=1;strokeColor=none;fillColor=none;align=center;verticalAlign=middle;fontSize=14;fontColor=#666666;" value="..." vertex="1">
<mxGeometry height="20" width="300" x="90" y="445" as="geometry" />
</mxCell>
<mxCell id="24" parent="1" style="text;html=1;strokeColor=none;fillColor=none;align=left;verticalAlign=middle;fontSize=12;" value="<font face="Courier New">1000 0001</font> → <b>-127</b>" vertex="1">
<mxGeometry height="25" width="300" x="90" y="465" as="geometry" />
</mxCell>
<mxCell id="25" parent="1" style="text;html=1;strokeColor=none;fillColor=none;align=left;verticalAlign=middle;fontSize=12;" value="<font face="Courier New">1000 0000</font> → <b>-128</b> (最小负数)" vertex="1">
<mxGeometry height="25" width="300" x="90" y="495" as="geometry" />
</mxCell>
<mxCell id="26" parent="1" style="rounded=1;whiteSpace=wrap;html=1;fillColor=#e8eaf6;strokeColor=#5c6bc0;strokeWidth=2;" value="" vertex="1">
<mxGeometry height="340" width="380" x="460" y="210" as="geometry" />
</mxCell>
<mxCell id="27" parent="1" style="text;html=1;strokeColor=none;fillColor=none;align=center;verticalAlign=middle;whiteSpace=wrap;rounded=0;fontSize=14;fontStyle=1;fontColor=#3949ab;" value="关键点" vertex="1">
<mxGeometry height="30" width="380" x="460" y="220" as="geometry" />
</mxCell>
<mxCell id="28" parent="1" style="rounded=1;whiteSpace=wrap;html=1;fillColor=#c8e6c9;strokeColor=#66bb6a;" value="" vertex="1">
<mxGeometry height="60" width="340" x="480" y="260" as="geometry" />
</mxCell>
<mxCell id="29" parent="1" style="text;html=1;strokeColor=none;fillColor=none;align=center;verticalAlign=middle;whiteSpace=wrap;rounded=0;fontSize=13;" value="<b>正数范围</b><br>0 ~ 2⁷-1 = <font color="#2e7d32"><b>0 ~ 127</b></font> (共 128 个)" vertex="1">
<mxGeometry height="60" width="340" x="480" y="260" as="geometry" />
</mxCell>
<mxCell id="30" parent="1" style="rounded=1;whiteSpace=wrap;html=1;fillColor=#ffcdd2;strokeColor=#ef5350;" value="" vertex="1">
<mxGeometry height="60" width="340" x="480" y="335" as="geometry" />
</mxCell>
<mxCell id="31" parent="1" style="text;html=1;strokeColor=none;fillColor=none;align=center;verticalAlign=middle;whiteSpace=wrap;rounded=0;fontSize=13;" value="<b>负数范围</b><br>-2⁷ ~ -1 = <font color="#c62828"><b>-128 ~ -1</b></font> (共 128 个)" vertex="1">
<mxGeometry height="60" width="340" x="480" y="335" as="geometry" />
</mxCell>
<mxCell id="32" parent="1" style="rounded=1;whiteSpace=wrap;html=1;fillColor=#bbdefb;strokeColor=#42a5f5;" value="" vertex="1">
<mxGeometry height="60" width="340" x="480" y="410" as="geometry" />
</mxCell>
<mxCell id="33" parent="1" style="text;html=1;strokeColor=none;fillColor=none;align=center;verticalAlign=middle;whiteSpace=wrap;rounded=0;fontSize=13;" value="<b>总共</b><br><font color="#1565c0"><b>256</b></font> 个不同的值 (2⁸ = 256)" vertex="1">
<mxGeometry height="60" width="340" x="480" y="410" as="geometry" />
</mxCell>
<mxCell id="34" parent="1" style="rounded=1;whiteSpace=wrap;html=1;fillColor=#fff9c4;strokeColor=#fbc02d;" value="" vertex="1">
<mxGeometry height="50" width="340" x="480" y="485" as="geometry" />
</mxCell>
<mxCell id="35" parent="1" style="text;html=1;strokeColor=none;fillColor=none;align=center;verticalAlign=middle;whiteSpace=wrap;rounded=0;fontSize=12;" value="💡 最大值要减1是因为 <b>0 占用了一个正数位置</b>" vertex="1">
<mxGeometry height="50" width="340" x="480" y="485" as="geometry" />
</mxCell>
<mxCell id="36" parent="1" style="rounded=1;whiteSpace=wrap;html=1;fillColor=#f3e5f5;strokeColor=#ab47bc;strokeWidth=2;" value="" vertex="1">
<mxGeometry height="50" width="790" x="50" y="570" as="geometry" />
</mxCell>
<mxCell id="37" parent="1" style="text;html=1;strokeColor=none;fillColor=none;align=center;verticalAlign=middle;whiteSpace=wrap;rounded=0;fontSize=14;" value="<b>结论：</b>byte 范围 = 128个负数 (-128 ~ -1) + 1个零 (0) + 127个正数 (1 ~ 127) = <font color="#7b1fa2"><b>-128 ~ 127</b></font>" vertex="1">
<mxGeometry height="50" width="790" x="50" y="570" as="geometry" />
</mxCell>
</root>
</mxGraphModel>
</diagram>
</mxfile>
2.2 整数字面量
// ═══════════════════════════════════════════════════════════════════════
// 整数字面量的各种表示形式
// ═══════════════════════════════════════════════════════════════════════
// 十进制（默认）
int decimal = 100;
// 二进制（0b 或 0B 开头，JDK 7+）
int binary = 0b1100100; // = 100
int binary2 = 0B1010_1010; // 可用下划线分隔，提高可读性
// 八进制（0 开头）
int octal = 0144; // = 100
// 十六进制（0x 或 0X 开头）
int hex = 0x64; // = 100
int hex2 = 0xFF; // = 255
// ═══════════════════════════════════════════════════════════════════════
// 长整型必须加 L 后缀
// ═══════════════════════════════════════════════════════════════════════
long small = 100; // OK，自动转换
long big = 10000000000L; // 必须加 L，否则编译错误
// long error = 10000000000; // ❌ 编译错误：整数太大
// 建议使用大写 L，小写 l 容易与数字 1 混淆
long value = 123456789L; // ✅ 推荐
long value2 = 123456789l; // ⚠️ 不推荐
// ═══════════════════════════════════════════════════════════════════════
// 数字中的下划线（JDK 7+）
// ═══════════════════════════════════════════════════════════════════════
int million = 1_000_000; // 一百万，更易读
long creditCard = 1234_5678_9012_3456L;
int binary3 = 0b1010_0101_1100_0011;
// 下划线的限制
// int error1 = _100; // ❌ 不能在开头
// int error2 = 100_; // ❌ 不能在结尾
// int error3 = 0_x64; // ❌ 不能在进制标识中
// double error4 = 3_.14; // ❌ 不能在小数点旁边
<mxfile>
<diagram id="java-integer-literals" name="整数字面量表示形式">
<mxGraphModel dx="1281" dy="581" grid="1" gridSize="10" guides="1" tooltips="1" connect="1" arrows="1" fold="1" page="1" pageScale="1" pageWidth="900" pageHeight="820" math="0" shadow="0">
<root>
<mxCell id="0" />
<mxCell id="1" parent="0" />
<mxCell id="2" parent="1" style="text;html=1;strokeColor=none;fillColor=none;align=center;verticalAlign=middle;fontSize=24;fontStyle=1;fontColor=#1E293B;" value="Java 整数字面量表示形式" vertex="1">
<mxGeometry height="40" width="400" x="250" y="20" as="geometry" />
</mxCell>
<mxCell id="3" parent="1" style="text;html=1;strokeColor=none;fillColor=#6366F1;align=center;verticalAlign=middle;fontSize=14;fontStyle=1;fontColor=#FFFFFF;rounded=1;" value="进制表示" vertex="1">
<mxGeometry height="30" width="100" x="40" y="70" as="geometry" />
</mxCell>
<mxCell id="4" parent="1" style="rounded=1;whiteSpace=wrap;html=1;fillColor=#EEF2FF;strokeColor=#6366F1;strokeWidth=2;" value="" vertex="1">
<mxGeometry height="200" width="820" x="40" y="110" as="geometry" />
</mxCell>
<mxCell id="5" parent="1" style="rounded=1;whiteSpace=wrap;html=1;fillColor=#3B82F6;strokeColor=#2563EB;strokeWidth=2;fontSize=13;fontStyle=1;fontColor=#FFFFFF;" value="十进制" vertex="1">
<mxGeometry height="35" width="180" x="60" y="130" as="geometry" />
</mxCell>
<mxCell id="6" parent="1" style="rounded=1;whiteSpace=wrap;html=1;fillColor=#F8FAFC;strokeColor=#CBD5E1;strokeWidth=1;fontSize=12;fontColor=#334155;align=left;spacingLeft=10;" value="<font face="Courier New">int decimal = 100;</font>" vertex="1">
<mxGeometry height="30" width="180" x="60" y="170" as="geometry" />
</mxCell>
<mxCell id="7" parent="1" style="text;html=1;strokeColor=none;fillColor=none;align=left;verticalAlign=middle;fontSize=11;fontColor=#64748B;spacingLeft=5;" value="默认格式，直接书写数字" vertex="1">
<mxGeometry height="20" width="180" x="60" y="200" as="geometry" />
</mxCell>
<mxCell id="8" parent="1" style="rounded=1;whiteSpace=wrap;html=1;fillColor=#22C55E;strokeColor=#16A34A;strokeWidth=2;fontSize=13;fontStyle=1;fontColor=#FFFFFF;" value="二进制 <font color="#ef4444">(JDK 7+)</font>" vertex="1">
<mxGeometry height="35" width="180" x="260" y="130" as="geometry" />
</mxCell>
<mxCell id="9" parent="1" style="rounded=1;whiteSpace=wrap;html=1;fillColor=#F8FAFC;strokeColor=#CBD5E1;strokeWidth=1;fontSize=12;fontColor=#334155;align=left;spacingLeft=10;" value="<font face="Courier New">int bin = <b>0b</b>1100100;</font>" vertex="1">
<mxGeometry height="30" width="180" x="260" y="170" as="geometry" />
</mxCell>
<mxCell id="10" parent="1" style="text;html=1;strokeColor=none;fillColor=none;align=left;verticalAlign=middle;fontSize=11;fontColor=#64748B;spacingLeft=5;" value="<b>0b</b> 或 <b>0B</b> 开头" vertex="1">
<mxGeometry height="20" width="180" x="260" y="200" as="geometry" />
</mxCell>
<mxCell id="11" parent="1" style="rounded=1;whiteSpace=wrap;html=1;fillColor=#F59E0B;strokeColor=#D97706;strokeWidth=2;fontSize=13;fontStyle=1;fontColor=#FFFFFF;" value="八进制" vertex="1">
<mxGeometry height="35" width="180" x="460" y="130" as="geometry" />
</mxCell>
<mxCell id="12" parent="1" style="rounded=1;whiteSpace=wrap;html=1;fillColor=#F8FAFC;strokeColor=#CBD5E1;strokeWidth=1;fontSize=12;fontColor=#334155;align=left;spacingLeft=10;" value="<font face="Courier New">int octal = <b>0</b>144;</font>" vertex="1">
<mxGeometry height="30" width="180" x="460" y="170" as="geometry" />
</mxCell>
<mxCell id="13" parent="1" style="text;html=1;strokeColor=none;fillColor=none;align=left;verticalAlign=middle;fontSize=11;fontColor=#64748B;spacingLeft=5;" value="<b>0</b> 开头（数字零）" vertex="1">
<mxGeometry height="20" width="180" x="460" y="200" as="geometry" />
</mxCell>
<mxCell id="14" parent="1" style="rounded=1;whiteSpace=wrap;html=1;fillColor=#EC4899;strokeColor=#DB2777;strokeWidth=2;fontSize=13;fontStyle=1;fontColor=#FFFFFF;" value="十六进制" vertex="1">
<mxGeometry height="35" width="180" x="660" y="130" as="geometry" />
</mxCell>
<mxCell id="15" parent="1" style="rounded=1;whiteSpace=wrap;html=1;fillColor=#F8FAFC;strokeColor=#CBD5E1;strokeWidth=1;fontSize=12;fontColor=#334155;align=left;spacingLeft=10;" value="<font face="Courier New">int hex = <b>0x</b>64;</font>" vertex="1">
<mxGeometry height="30" width="180" x="660" y="170" as="geometry" />
</mxCell>
<mxCell id="16" parent="1" style="text;html=1;strokeColor=none;fillColor=none;align=left;verticalAlign=middle;fontSize=11;fontColor=#64748B;spacingLeft=5;" value="<b>0x</b> 或 <b>0X</b> 开头" vertex="1">
<mxGeometry height="20" width="180" x="660" y="200" as="geometry" />
</mxCell>
<mxCell id="17" parent="1" style="ellipse;whiteSpace=wrap;html=1;fillColor=#DBEAFE;strokeColor=#3B82F6;strokeWidth=1;fontSize=11;fontStyle=1;fontColor=#1E40AF;" value="= 100" vertex="1">
<mxGeometry height="30" width="60" x="120" y="230" as="geometry" />
</mxCell>
<mxCell id="18" parent="1" style="ellipse;whiteSpace=wrap;html=1;fillColor=#DCFCE7;strokeColor=#22C55E;strokeWidth=1;fontSize=11;fontStyle=1;fontColor=#166534;" value="= 100" vertex="1">
<mxGeometry height="30" width="60" x="320" y="230" as="geometry" />
</mxCell>
<mxCell id="19" parent="1" style="ellipse;whiteSpace=wrap;html=1;fillColor=#FEF3C7;strokeColor=#F59E0B;strokeWidth=1;fontSize=11;fontStyle=1;fontColor=#92400E;" value="= 100" vertex="1">
<mxGeometry height="30" width="60" x="520" y="230" as="geometry" />
</mxCell>
<mxCell id="20" parent="1" style="ellipse;whiteSpace=wrap;html=1;fillColor=#FCE7F3;strokeColor=#EC4899;strokeWidth=1;fontSize=11;fontStyle=1;fontColor=#9D174D;" value="= 100" vertex="1">
<mxGeometry height="30" width="60" x="720" y="230" as="geometry" />
</mxCell>
<mxCell id="21" parent="1" style="text;html=1;strokeColor=none;fillColor=#FDF2F8;align=center;verticalAlign=middle;fontSize=10;fontColor=#9D174D;rounded=1;" value="<font face="Courier New">0xFF = 255</font>" vertex="1">
<mxGeometry height="20" width="70" x="715" y="270" as="geometry" />
</mxCell>
<mxCell id="22" parent="1" style="text;html=1;strokeColor=none;fillColor=#F0FDF4;align=center;verticalAlign=middle;fontSize=10;fontColor=#166534;rounded=1;" value="<font face="Courier New">0b1010_1010</font>" vertex="1">
<mxGeometry height="20" width="90" x="260" y="270" as="geometry" />
</mxCell>
<mxCell id="23" parent="1" style="text;html=1;strokeColor=none;fillColor=none;align=left;verticalAlign=middle;fontSize=10;fontColor=#64748B;" value="可用下划线分隔" vertex="1">
<mxGeometry height="20" width="85" x="355" y="270" as="geometry" />
</mxCell>
<mxCell id="24" parent="1" style="text;html=1;strokeColor=none;fillColor=#8B5CF6;align=center;verticalAlign=middle;fontSize=14;fontStyle=1;fontColor=#FFFFFF;rounded=1;" value="长整型 L 后缀" vertex="1">
<mxGeometry height="30" width="120" x="40" y="320" as="geometry" />
</mxCell>
<mxCell id="25" parent="1" style="rounded=1;whiteSpace=wrap;html=1;fillColor=#F5F3FF;strokeColor=#8B5CF6;strokeWidth=2;" value="" vertex="1">
<mxGeometry height="150" width="820" x="40" y="360" as="geometry" />
</mxCell>
<mxCell id="26" parent="1" style="rounded=1;whiteSpace=wrap;html=1;fillColor=#22C55E;strokeColor=#16A34A;strokeWidth=1;fontSize=12;fontStyle=1;fontColor=#FFFFFF;" value="✅ 正确用法" vertex="1">
<mxGeometry height="25" width="360" x="60" y="375" as="geometry" />
</mxCell>
<mxCell id="27" parent="1" style="rounded=0;whiteSpace=wrap;html=1;fillColor=#F8FAFC;strokeColor=#CBD5E1;strokeWidth=1;fontSize=11;fontColor=#334155;align=left;spacingLeft=10;" value="<font face="Courier New">long small = 100;</font> <font color="#64748b">// 自动转换</font>" vertex="1">
<mxGeometry height="28" width="360" x="60" y="405" as="geometry" />
</mxCell>
<mxCell id="28" parent="1" style="rounded=0;whiteSpace=wrap;html=1;fillColor=#F8FAFC;strokeColor=#CBD5E1;strokeWidth=1;fontSize=11;fontColor=#334155;align=left;spacingLeft=10;" value="<font face="Courier New">long big = 10000000000<b>L</b>;</font> <font color="#64748b">// 必须加 L</font>" vertex="1">
<mxGeometry height="28" width="360" x="60" y="433" as="geometry" />
</mxCell>
<mxCell id="29" parent="1" style="rounded=0;whiteSpace=wrap;html=1;fillColor=#F0FDF4;strokeColor=#86EFAC;strokeWidth=1;fontSize=11;fontColor=#334155;align=left;spacingLeft=10;" value="<font face="Courier New">long value = 123456789<b>L</b>;</font> <font color="#22c55e">// 推荐大写 L</font>" vertex="1">
<mxGeometry height="28" width="360" x="60" y="461" as="geometry" />
</mxCell>
<mxCell id="30" parent="1" style="rounded=1;whiteSpace=wrap;html=1;fillColor=#EF4444;strokeColor=#DC2626;strokeWidth=1;fontSize=12;fontStyle=1;fontColor=#FFFFFF;" value="❌ 错误用法" vertex="1">
<mxGeometry height="25" width="400" x="440" y="375" as="geometry" />
</mxCell>
<mxCell id="31" parent="1" style="rounded=0;whiteSpace=wrap;html=1;fillColor=#FEF2F2;strokeColor=#FECACA;strokeWidth=1;fontSize=11;fontColor=#334155;align=left;spacingLeft=10;" value="<font face="Courier New">long error = 10000000000;</font> <font color="#ef4444">// 编译错误：整数太大</font>" vertex="1">
<mxGeometry height="28" width="400" x="440" y="405" as="geometry" />
</mxCell>
<mxCell id="32" parent="1" style="rounded=0;whiteSpace=wrap;html=1;fillColor=#FFFBEB;strokeColor=#FDE68A;strokeWidth=1;fontSize=11;fontColor=#334155;align=left;spacingLeft=10;" value="<font face="Courier New">long value2 = 123456789<b>l</b>;</font> <font color="#f59e0b">// 不推荐：l 易与 1 混淆</font>" vertex="1">
<mxGeometry height="28" width="400" x="440" y="433" as="geometry" />
</mxCell>
<mxCell id="33" parent="1" style="text;html=1;strokeColor=none;fillColor=#DDD6FE;align=center;verticalAlign=middle;fontSize=11;fontColor=#5B21B6;rounded=1;spacingLeft=5;spacingRight=5;" value="💡 超过 int 范围（约21亿）的数字必须加 L 后缀" vertex="1">
<mxGeometry height="24" width="300" x="440" y="468" as="geometry" />
</mxCell>
<mxCell id="34" parent="1" style="text;html=1;strokeColor=none;fillColor=#0EA5E9;align=center;verticalAlign=middle;fontSize=14;fontStyle=1;fontColor=#FFFFFF;rounded=1;" value="数字下划线 <font color="#ef4444">(JDK 7+)</font>" vertex="1">
<mxGeometry height="30" width="160" x="40" y="520" as="geometry" />
</mxCell>
<mxCell id="35" parent="1" style="rounded=1;whiteSpace=wrap;html=1;fillColor=#F0F9FF;strokeColor=#0EA5E9;strokeWidth=2;" value="" vertex="1">
<mxGeometry height="200" width="820" x="40" y="560" as="geometry" />
</mxCell>
<mxCell id="36" parent="1" style="rounded=1;whiteSpace=wrap;html=1;fillColor=#22C55E;strokeColor=#16A34A;strokeWidth=1;fontSize=12;fontStyle=1;fontColor=#FFFFFF;" value="✅ 合法位置" vertex="1">
<mxGeometry height="25" width="360" x="60" y="575" as="geometry" />
</mxCell>
<mxCell id="37" parent="1" style="rounded=0;whiteSpace=wrap;html=1;fillColor=#F8FAFC;strokeColor=#CBD5E1;strokeWidth=1;fontSize=11;fontColor=#334155;align=left;spacingLeft=10;" value="<font face="Courier New">int million = 1<b>_</b>000<b>_</b>000;</font><font color="#64748b">// 一百万</font>" vertex="1">
<mxGeometry height="28" width="360" x="60" y="605" as="geometry" />
</mxCell>
<mxCell id="38" parent="1" style="rounded=0;whiteSpace=wrap;html=1;fillColor=#F8FAFC;strokeColor=#CBD5E1;strokeWidth=1;fontSize=11;fontColor=#334155;align=left;spacingLeft=10;" value="<font face="Courier New">long card = 1234<b>_</b>5678<b>_</b>9012<b>_</b>3456L;</font> <font color="#64748b">// 信用卡号</font>" vertex="1">
<mxGeometry height="28" width="360" x="60" y="633" as="geometry" />
</mxCell>
<mxCell id="39" parent="1" style="rounded=0;whiteSpace=wrap;html=1;fillColor=#F8FAFC;strokeColor=#CBD5E1;strokeWidth=1;fontSize=11;fontColor=#334155;align=left;spacingLeft=10;" value="<font face="Courier New">int bin = 0b1010<b>_</b>0101<b>_</b>1100<b>_</b>0011;</font> <font color="#64748b">// 二进制</font>" vertex="1">
<mxGeometry height="28" width="360" x="60" y="661" as="geometry" />
</mxCell>
<mxCell id="40" parent="1" style="rounded=1;whiteSpace=wrap;html=1;fillColor=#EF4444;strokeColor=#DC2626;strokeWidth=1;fontSize=12;fontStyle=1;fontColor=#FFFFFF;" value="❌ 非法位置" vertex="1">
<mxGeometry height="25" width="400" x="440" y="575" as="geometry" />
</mxCell>
<mxCell id="41" parent="1" style="rounded=0;whiteSpace=wrap;html=1;fillColor=#FEF2F2;strokeColor=#FECACA;strokeWidth=1;fontSize=11;fontColor=#334155;align=center;" value="<font face="Courier New"><b>_</b>100</font>" vertex="1">
<mxGeometry height="28" width="80" x="440" y="605" as="geometry" />
</mxCell>
<mxCell id="42" parent="1" style="text;html=1;strokeColor=none;fillColor=none;align=center;verticalAlign=middle;fontSize=10;fontColor=#EF4444;" value="开头" vertex="1">
<mxGeometry height="28" width="40" x="520" y="605" as="geometry" />
</mxCell>
<mxCell id="43" parent="1" style="rounded=0;whiteSpace=wrap;html=1;fillColor=#FEF2F2;strokeColor=#FECACA;strokeWidth=1;fontSize=11;fontColor=#334155;align=center;" value="<font face="Courier New">100<b>_</b></font>" vertex="1">
<mxGeometry height="28" width="80" x="570" y="605" as="geometry" />
</mxCell>
<mxCell id="44" parent="1" style="text;html=1;strokeColor=none;fillColor=none;align=center;verticalAlign=middle;fontSize=10;fontColor=#EF4444;" value="结尾" vertex="1">
<mxGeometry height="28" width="40" x="650" y="605" as="geometry" />
</mxCell>
<mxCell id="45" parent="1" style="rounded=0;whiteSpace=wrap;html=1;fillColor=#FEF2F2;strokeColor=#FECACA;strokeWidth=1;fontSize=11;fontColor=#334155;align=center;" value="<font face="Courier New">0<b>_</b>x64</font>" vertex="1">
<mxGeometry height="28" width="80" x="700" y="605" as="geometry" />
</mxCell>
<mxCell id="46" parent="1" style="text;html=1;strokeColor=none;fillColor=none;align=center;verticalAlign=middle;fontSize=10;fontColor=#EF4444;" value="进制标识中" vertex="1">
<mxGeometry height="28" width="60" x="780" y="605" as="geometry" />
</mxCell>
<mxCell id="47" parent="1" style="rounded=0;whiteSpace=wrap;html=1;fillColor=#FEF2F2;strokeColor=#FECACA;strokeWidth=1;fontSize=11;fontColor=#334155;align=center;" value="<font face="Courier New">3<b>_</b>.14</font>" vertex="1">
<mxGeometry height="28" width="80" x="440" y="643" as="geometry" />
</mxCell>
<mxCell id="48" parent="1" style="rounded=0;whiteSpace=wrap;html=1;fillColor=#FEF2F2;strokeColor=#FECACA;strokeWidth=1;fontSize=11;fontColor=#334155;align=center;" value="<font face="Courier New">3.<b>_</b>14</font>" vertex="1">
<mxGeometry height="28" width="80" x="570" y="643" as="geometry" />
</mxCell>
<mxCell id="49" parent="1" style="text;html=1;strokeColor=none;fillColor=none;align=center;verticalAlign=middle;fontSize=10;fontColor=#EF4444;" value="小数点旁边" vertex="1">
<mxGeometry height="28" width="50" x="520" y="643" as="geometry" />
</mxCell>
<mxCell id="50" parent="1" style="rounded=0;whiteSpace=wrap;html=1;fillColor=#FEF2F2;strokeColor=#FECACA;strokeWidth=1;fontSize=11;fontColor=#334155;align=center;" value="<font face="Courier New">1.0<b>_</b>e10</font>" vertex="1">
<mxGeometry height="28" width="80" x="700" y="643" as="geometry" />
</mxCell>
<mxCell id="51" parent="1" style="text;html=1;strokeColor=none;fillColor=none;align=center;verticalAlign=middle;fontSize=10;fontColor=#EF4444;" value="指数符号旁" vertex="1">
<mxGeometry height="28" width="60" x="780" y="643" as="geometry" />
</mxCell>
<mxCell id="52" parent="1" style="text;html=1;strokeColor=none;fillColor=#E0F2FE;align=center;verticalAlign=middle;fontSize=11;fontColor=#0369A1;rounded=1;spacingLeft=5;spacingRight=5;" value="💡 下划线只能放在数字之间，用于提高大数字的可读性" vertex="1">
<mxGeometry height="24" width="340" x="60" y="700" as="geometry" />
</mxCell>
<mxCell id="53" parent="1" style="rounded=1;whiteSpace=wrap;html=1;fillColor=#F1F5F9;strokeColor=#94A3B8;strokeWidth=2;dashed=1;" value="" vertex="1">
<mxGeometry height="55" width="400" x="440" y="690" as="geometry" />
</mxCell>
<mxCell id="54" parent="1" style="text;html=1;strokeColor=none;fillColor=#64748B;align=center;verticalAlign=middle;fontSize=11;fontStyle=1;fontColor=#FFFFFF;rounded=1;" value="记忆口诀" vertex="1">
<mxGeometry height="18" width="60" x="450" y="698" as="geometry" />
</mxCell>
<mxCell id="55" parent="1" style="text;html=1;strokeColor=none;fillColor=none;align=center;verticalAlign=middle;fontSize=11;fontColor=#475569;" value="<b>0b</b> 二进制 | <b>0</b> 八进制 | <b>0x</b> 十六进制 | <b>L</b> 长整型 | <b>_</b> 分隔符" vertex="1">
<mxGeometry height="20" width="380" x="450" y="718" as="geometry" />
</mxCell>
</root>
</mxGraphModel>
</diagram>
</mxfile>
2.3 整数溢出
public class OverflowDemo {
public static void main(String[] args) {
// 最大值 + 1 = 最小值（溢出）
int max = Integer.MAX_VALUE; // 2147483647
System.out.println("max = " + max);
System.out.println("max + 1 = " + (max + 1)); // -2147483648
// 最小值 - 1 = 最大值（下溢）
int min = Integer.MIN_VALUE; // -2147483648
System.out.println("min = " + min);
System.out.println("min - 1 = " + (min - 1)); // 2147483647
}
}
<mxfile>
<diagram id="integer-overflow" name="整数溢出图解">
<mxGraphModel dx="610" dy="277" grid="1" gridSize="10" guides="1" tooltips="1" connect="1" arrows="1" fold="1" page="1" pageScale="1" pageWidth="900" pageHeight="700" math="0" shadow="0">
<root>
<mxCell id="0" />
<mxCell id="1" parent="0" />
<mxCell id="2" parent="1" style="text;html=1;strokeColor=none;fillColor=none;align=center;verticalAlign=middle;fontSize=24;fontStyle=1;fontColor=#1E293B;" value="整数溢出图解" vertex="1">
<mxGeometry height="40" width="300" x="300" y="20" as="geometry" />
</mxCell>
<mxCell id="3" parent="1" style="text;html=1;strokeColor=none;fillColor=#F1F5F9;align=center;verticalAlign=middle;fontSize=14;fontColor=#475569;rounded=1;spacingLeft=10;spacingRight=10;" value="以 <font face="Courier New" color="#6366f1"><b>byte</b></font> 为例（-128 ~ 127）" vertex="1">
<mxGeometry height="30" width="260" x="320" y="70" as="geometry" />
</mxCell>
<mxCell id="4" parent="1" style="ellipse;whiteSpace=wrap;html=1;fillColor=none;strokeColor=#6366F1;strokeWidth=8;" value="" vertex="1">
<mxGeometry height="300" width="300" x="300" y="120" as="geometry" />
</mxCell>
<mxCell id="5" parent="1" style="ellipse;whiteSpace=wrap;html=1;fillColor=#EEF2FF;strokeColor=none;" value="" vertex="1">
<mxGeometry height="200" width="200" x="350" y="170" as="geometry" />
</mxCell>
<mxCell id="6" parent="1" style="text;html=1;strokeColor=none;fillColor=none;align=center;verticalAlign=middle;fontSize=16;fontStyle=1;fontColor=#4F46E5;" value="数值范围环" vertex="1">
<mxGeometry height="30" width="130" x="385" y="250" as="geometry" />
</mxCell>
<mxCell id="7" parent="1" style="text;html=1;strokeColor=none;fillColor=none;align=center;verticalAlign=middle;fontSize=12;fontColor=#6366F1;" value="byte 类型" vertex="1">
<mxGeometry height="20" width="100" x="400" y="280" as="geometry" />
</mxCell>
<mxCell id="8" parent="1" style="rounded=1;whiteSpace=wrap;html=1;fillColor=#22C55E;strokeColor=#16A34A;strokeWidth=2;fontSize=18;fontStyle=1;fontColor=#FFFFFF;" value="127" vertex="1">
<mxGeometry height="40" width="70" x="610" y="250" as="geometry" />
</mxCell>
<mxCell id="9" parent="1" style="rounded=1;whiteSpace=wrap;html=1;fillColor=#EF4444;strokeColor=#DC2626;strokeWidth=2;fontSize=18;fontStyle=1;fontColor=#FFFFFF;" value="-128" vertex="1">
<mxGeometry height="40" width="70" x="220" y="250" as="geometry" />
</mxCell>
<mxCell id="10" parent="1" style="rounded=1;whiteSpace=wrap;html=1;fillColor=#3B82F6;strokeColor=#2563EB;strokeWidth=2;fontSize=14;fontStyle=1;fontColor=#FFFFFF;" value="0" vertex="1">
<mxGeometry height="30" width="50" x="425" y="110" as="geometry" />
</mxCell>
<mxCell id="11" parent="1" style="text;html=1;strokeColor=none;fillColor=none;align=center;verticalAlign=middle;fontSize=10;fontStyle=1;fontColor=#16A34A;" value="MAX" vertex="1">
<mxGeometry height="15" width="50" x="620" y="290" as="geometry" />
</mxCell>
<mxCell id="12" parent="1" style="text;html=1;strokeColor=none;fillColor=none;align=center;verticalAlign=middle;fontSize=10;fontStyle=1;fontColor=#DC2626;" value="MIN" vertex="1">
<mxGeometry height="15" width="50" x="230" y="290" as="geometry" />
</mxCell>
<mxCell id="13" edge="1" parent="1" source="8" style="curved=1;endArrow=classic;html=1;strokeWidth=3;strokeColor=#F59E0B;endFill=1;exitX=1;exitY=0.5;exitDx=0;exitDy=0;entryX=0;entryY=0.5;entryDx=0;entryDy=0;" target="9" value="">
<mxGeometry height="50" relative="1" width="50" as="geometry">
<Array as="points">
<mxPoint x="720" y="270" />
<mxPoint x="750" y="350" />
<mxPoint x="720" y="450" />
<mxPoint x="450" y="480" />
<mxPoint x="180" y="450" />
<mxPoint x="150" y="350" />
<mxPoint x="180" y="270" />
</Array>
<mxPoint x="700" y="270" as="sourcePoint" />
<mxPoint x="220" y="270" as="targetPoint" />
</mxGeometry>
</mxCell>
<mxCell id="14" parent="1" style="text;html=1;strokeColor=none;fillColor=#FEF3C7;align=center;verticalAlign=middle;fontSize=14;fontColor=#92400E;rounded=1;spacingLeft=10;spacingRight=10;" value="<font face="Courier New"><b>127 + 1 = -128</b></font>" vertex="1">
<mxGeometry height="30" width="170" x="365" y="430" as="geometry" />
</mxCell>
<mxCell id="15" parent="1" style="text;html=1;strokeColor=none;fillColor=#FEE2E2;align=center;verticalAlign=middle;fontSize=12;fontStyle=1;fontColor=#DC2626;rounded=1;" value="溢出!" vertex="1">
<mxGeometry height="20" width="50" x="430" y="475" as="geometry" />
</mxCell>
<mxCell id="16" parent="1" style="text;html=1;strokeColor=none;fillColor=#DBEAFE;align=center;verticalAlign=middle;fontSize=11;fontStyle=1;fontColor=#1E40AF;rounded=1;" value="64" vertex="1">
<mxGeometry height="20" width="35" x="555" y="145" as="geometry" />
</mxCell>
<mxCell id="17" parent="1" style="text;html=1;strokeColor=none;fillColor=#DBEAFE;align=center;verticalAlign=middle;fontSize=11;fontStyle=1;fontColor=#1E40AF;rounded=1;" value="-64" vertex="1">
<mxGeometry height="20" width="35" x="310" y="145" as="geometry" />
</mxCell>
<mxCell id="18" parent="1" style="text;html=1;strokeColor=none;fillColor=#8B5CF6;align=center;verticalAlign=middle;fontSize=14;fontStyle=1;fontColor=#FFFFFF;rounded=1;" value="二进制层面分析" vertex="1">
<mxGeometry height="30" width="140" x="40" y="520" as="geometry" />
</mxCell>
<mxCell id="19" parent="1" style="rounded=1;whiteSpace=wrap;html=1;fillColor=#FAF5FF;strokeColor=#8B5CF6;strokeWidth=2;" value="" vertex="1">
<mxGeometry height="120" width="820" x="40" y="560" as="geometry" />
</mxCell>
<mxCell id="20" parent="1" style="text;html=1;strokeColor=none;fillColor=none;align=right;verticalAlign=middle;fontSize=14;fontStyle=1;fontColor=#475569;fontFamily=Courier New;" value="127:" vertex="1">
<mxGeometry height="25" width="60" x="60" y="575" as="geometry" />
</mxCell>
<mxCell id="21" parent="1" style="rounded=0;whiteSpace=wrap;html=1;fillColor=#DCFCE7;strokeColor=#86EFAC;strokeWidth=1;fontSize=16;fontStyle=1;fontColor=#166534;fontFamily=Courier New;" value="0" vertex="1">
<mxGeometry height="30" width="35" x="130" y="575" as="geometry" />
</mxCell>
<mxCell id="22" parent="1" style="rounded=0;whiteSpace=wrap;html=1;fillColor=#F1F5F9;strokeColor=#CBD5E1;strokeWidth=1;fontSize=16;fontStyle=1;fontColor=#334155;fontFamily=Courier New;" value="1" vertex="1">
<mxGeometry height="30" width="35" x="165" y="575" as="geometry" />
</mxCell>
<mxCell id="23" parent="1" style="rounded=0;whiteSpace=wrap;html=1;fillColor=#F1F5F9;strokeColor=#CBD5E1;strokeWidth=1;fontSize=16;fontStyle=1;fontColor=#334155;fontFamily=Courier New;" value="1" vertex="1">
<mxGeometry height="30" width="35" x="200" y="575" as="geometry" />
</mxCell>
<mxCell id="24" parent="1" style="rounded=0;whiteSpace=wrap;html=1;fillColor=#F1F5F9;strokeColor=#CBD5E1;strokeWidth=1;fontSize=16;fontStyle=1;fontColor=#334155;fontFamily=Courier New;" value="1" vertex="1">
<mxGeometry height="30" width="35" x="235" y="575" as="geometry" />
</mxCell>
<mxCell id="25" parent="1" style="rounded=0;whiteSpace=wrap;html=1;fillColor=#F1F5F9;strokeColor=#CBD5E1;strokeWidth=1;fontSize=16;fontStyle=1;fontColor=#334155;fontFamily=Courier New;" value="1" vertex="1">
<mxGeometry height="30" width="35" x="280" y="575" as="geometry" />
</mxCell>
<mxCell id="26" parent="1" style="rounded=0;whiteSpace=wrap;html=1;fillColor=#F1F5F9;strokeColor=#CBD5E1;strokeWidth=1;fontSize=16;fontStyle=1;fontColor=#334155;fontFamily=Courier New;" value="1" vertex="1">
<mxGeometry height="30" width="35" x="315" y="575" as="geometry" />
</mxCell>
<mxCell id="27" parent="1" style="rounded=0;whiteSpace=wrap;html=1;fillColor=#F1F5F9;strokeColor=#CBD5E1;strokeWidth=1;fontSize=16;fontStyle=1;fontColor=#334155;fontFamily=Courier New;" value="1" vertex="1">
<mxGeometry height="30" width="35" x="350" y="575" as="geometry" />
</mxCell>
<mxCell id="28" parent="1" style="rounded=0;whiteSpace=wrap;html=1;fillColor=#F1F5F9;strokeColor=#CBD5E1;strokeWidth=1;fontSize=16;fontStyle=1;fontColor=#334155;fontFamily=Courier New;" value="1" vertex="1">
<mxGeometry height="30" width="35" x="385" y="575" as="geometry" />
</mxCell>
<mxCell id="29" parent="1" style="text;html=1;strokeColor=none;fillColor=none;align=right;verticalAlign=middle;fontSize=14;fontStyle=1;fontColor=#475569;fontFamily=Courier New;" value="+ 1:" vertex="1">
<mxGeometry height="25" width="60" x="60" y="605" as="geometry" />
</mxCell>
<mxCell id="30" parent="1" style="rounded=0;whiteSpace=wrap;html=1;fillColor=#F1F5F9;strokeColor=#CBD5E1;strokeWidth=1;fontSize=16;fontColor=#94A3B8;fontFamily=Courier New;" value="0" vertex="1">
<mxGeometry height="30" width="35" x="130" y="605" as="geometry" />
</mxCell>
<mxCell id="31" parent="1" style="rounded=0;whiteSpace=wrap;html=1;fillColor=#F1F5F9;strokeColor=#CBD5E1;strokeWidth=1;fontSize=16;fontColor=#94A3B8;fontFamily=Courier New;" value="0" vertex="1">
<mxGeometry height="30" width="35" x="165" y="605" as="geometry" />
</mxCell>
<mxCell id="32" parent="1" style="rounded=0;whiteSpace=wrap;html=1;fillColor=#F1F5F9;strokeColor=#CBD5E1;strokeWidth=1;fontSize=16;fontColor=#94A3B8;fontFamily=Courier New;" value="0" vertex="1">
<mxGeometry height="30" width="35" x="200" y="605" as="geometry" />
</mxCell>
<mxCell id="33" parent="1" style="rounded=0;whiteSpace=wrap;html=1;fillColor=#F1F5F9;strokeColor=#CBD5E1;strokeWidth=1;fontSize=16;fontColor=#94A3B8;fontFamily=Courier New;" value="0" vertex="1">
<mxGeometry height="30" width="35" x="235" y="605" as="geometry" />
</mxCell>
<mxCell id="34" parent="1" style="rounded=0;whiteSpace=wrap;html=1;fillColor=#F1F5F9;strokeColor=#CBD5E1;strokeWidth=1;fontSize=16;fontColor=#94A3B8;fontFamily=Courier New;" value="0" vertex="1">
<mxGeometry height="30" width="35" x="280" y="605" as="geometry" />
</mxCell>
<mxCell id="35" parent="1" style="rounded=0;whiteSpace=wrap;html=1;fillColor=#F1F5F9;strokeColor=#CBD5E1;strokeWidth=1;fontSize=16;fontColor=#94A3B8;fontFamily=Courier New;" value="0" vertex="1">
<mxGeometry height="30" width="35" x="315" y="605" as="geometry" />
</mxCell>
<mxCell id="36" parent="1" style="rounded=0;whiteSpace=wrap;html=1;fillColor=#F1F5F9;strokeColor=#CBD5E1;strokeWidth=1;fontSize=16;fontColor=#94A3B8;fontFamily=Courier New;" value="0" vertex="1">
<mxGeometry height="30" width="35" x="350" y="605" as="geometry" />
</mxCell>
<mxCell id="37" parent="1" style="rounded=0;whiteSpace=wrap;html=1;fillColor=#DBEAFE;strokeColor=#93C5FD;strokeWidth=1;fontSize=16;fontStyle=1;fontColor=#1E40AF;fontFamily=Courier New;" value="1" vertex="1">
<mxGeometry height="30" width="35" x="385" y="605" as="geometry" />
</mxCell>
<mxCell id="38" edge="1" parent="1" style="endArrow=none;html=1;strokeWidth=2;strokeColor=#64748B;" value="">
<mxGeometry height="50" relative="1" width="50" as="geometry">
<mxPoint x="130" y="640" as="sourcePoint" />
<mxPoint x="420" y="640" as="targetPoint" />
</mxGeometry>
</mxCell>
<mxCell id="39" parent="1" style="text;html=1;strokeColor=none;fillColor=none;align=right;verticalAlign=middle;fontSize=14;fontStyle=1;fontColor=#475569;fontFamily=Courier New;" value="结果:" vertex="1">
<mxGeometry height="25" width="60" x="60" y="645" as="geometry" />
</mxCell>
<mxCell id="40" parent="1" style="rounded=0;whiteSpace=wrap;html=1;fillColor=#FEE2E2;strokeColor=#FECACA;strokeWidth=2;fontSize=16;fontStyle=1;fontColor=#DC2626;fontFamily=Courier New;" value="1" vertex="1">
<mxGeometry height="30" width="35" x="130" y="645" as="geometry" />
</mxCell>
<mxCell id="41" parent="1" style="rounded=0;whiteSpace=wrap;html=1;fillColor=#F1F5F9;strokeColor=#CBD5E1;strokeWidth=1;fontSize=16;fontColor=#94A3B8;fontFamily=Courier New;" value="0" vertex="1">
<mxGeometry height="30" width="35" x="165" y="645" as="geometry" />
</mxCell>
<mxCell id="42" parent="1" style="rounded=0;whiteSpace=wrap;html=1;fillColor=#F1F5F9;strokeColor=#CBD5E1;strokeWidth=1;fontSize=16;fontColor=#94A3B8;fontFamily=Courier New;" value="0" vertex="1">
<mxGeometry height="30" width="35" x="200" y="645" as="geometry" />
</mxCell>
<mxCell id="43" parent="1" style="rounded=0;whiteSpace=wrap;html=1;fillColor=#F1F5F9;strokeColor=#CBD5E1;strokeWidth=1;fontSize=16;fontColor=#94A3B8;fontFamily=Courier New;" value="0" vertex="1">
<mxGeometry height="30" width="35" x="235" y="645" as="geometry" />
</mxCell>
<mxCell id="44" parent="1" style="rounded=0;whiteSpace=wrap;html=1;fillColor=#F1F5F9;strokeColor=#CBD5E1;strokeWidth=1;fontSize=16;fontColor=#94A3B8;fontFamily=Courier New;" value="0" vertex="1">
<mxGeometry height="30" width="35" x="280" y="645" as="geometry" />
</mxCell>
<mxCell id="45" parent="1" style="rounded=0;whiteSpace=wrap;html=1;fillColor=#F1F5F9;strokeColor=#CBD5E1;strokeWidth=1;fontSize=16;fontColor=#94A3B8;fontFamily=Courier New;" value="0" vertex="1">
<mxGeometry height="30" width="35" x="315" y="645" as="geometry" />
</mxCell>
<mxCell id="46" parent="1" style="rounded=0;whiteSpace=wrap;html=1;fillColor=#F1F5F9;strokeColor=#CBD5E1;strokeWidth=1;fontSize=16;fontColor=#94A3B8;fontFamily=Courier New;" value="0" vertex="1">
<mxGeometry height="30" width="35" x="350" y="645" as="geometry" />
</mxCell>
<mxCell id="47" parent="1" style="rounded=0;whiteSpace=wrap;html=1;fillColor=#F1F5F9;strokeColor=#CBD5E1;strokeWidth=1;fontSize=16;fontColor=#94A3B8;fontFamily=Courier New;" value="0" vertex="1">
<mxGeometry height="30" width="35" x="385" y="645" as="geometry" />
</mxCell>
<mxCell id="48" parent="1" style="text;html=1;strokeColor=none;fillColor=none;align=center;verticalAlign=middle;fontSize=10;fontColor=#DC2626;" value="符号位" vertex="1">
<mxGeometry height="20" width="45" x="125" y="555" as="geometry" />
</mxCell>
<mxCell id="50" parent="1" style="text;html=1;strokeColor=none;fillColor=none;align=center;verticalAlign=middle;fontSize=24;fontStyle=1;fontColor=#8B5CF6;" value="→" vertex="1">
<mxGeometry height="40" width="40" x="430" y="605" as="geometry" />
</mxCell>
<mxCell id="51" parent="1" style="rounded=1;whiteSpace=wrap;html=1;fillColor=#EF4444;strokeColor=#DC2626;strokeWidth=2;fontSize=24;fontStyle=1;fontColor=#FFFFFF;" value="-128" vertex="1">
<mxGeometry height="50" width="100" x="480" y="600" as="geometry" />
</mxCell>
<mxCell id="52" parent="1" style="text;html=1;strokeColor=none;fillColor=#FEF2F2;align=center;verticalAlign=middle;fontSize=11;fontColor=#991B1B;rounded=1;" value="最高位进位<br>变成符号位" vertex="1">
<mxGeometry height="40" width="80" x="590" y="605" as="geometry" />
</mxCell>
<mxCell id="53" parent="1" style="rounded=1;whiteSpace=wrap;html=1;fillColor=#FEF2F2;strokeColor=#EF4444;strokeWidth=2;" value="" vertex="1">
<mxGeometry height="100" width="160" x="690" y="570" as="geometry" />
</mxCell>
<mxCell id="54" parent="1" style="text;html=1;strokeColor=none;fillColor=#EF4444;align=center;verticalAlign=middle;fontSize=12;fontStyle=1;fontColor=#FFFFFF;rounded=1;" value="⚠️ 注意" vertex="1">
<mxGeometry height="20" width="60" x="700" y="580" as="geometry" />
</mxCell>
<mxCell id="55" parent="1" style="text;html=1;strokeColor=none;fillColor=none;align=center;verticalAlign=middle;fontSize=12;fontColor=#991B1B;" value="Java 不会自动检测溢出<br>需要程序员自行处理！" vertex="1">
<mxGeometry height="50" width="150" x="695" y="610" as="geometry" />
</mxCell>
<mxCell id="56" parent="1" style="text;html=1;strokeColor=none;fillColor=#DCFCE7;align=center;verticalAlign=middle;fontSize=10;fontStyle=1;fontColor=#166534;rounded=1;" value="正数" vertex="1">
<mxGeometry height="15" width="35" x="130" y="595" as="geometry" />
</mxCell>
<mxCell id="57" parent="1" style="text;html=1;strokeColor=none;fillColor=#FEE2E2;align=center;verticalAlign=middle;fontSize=10;fontStyle=1;fontColor=#991B1B;rounded=1;" value="负数" vertex="1">
<mxGeometry height="15" width="35" x="130" y="665" as="geometry" />
</mxCell>
</root>
</mxGraphModel>
</diagram>
</mxfile>
安全的算术运算：
// JDK 8+ 提供安全的算术方法，溢出时抛出异常
public class SafeMathDemo {
public static void main(String[] args) {
int a = Integer.MAX_VALUE;
int b = 1;
// 普通加法（静默溢出）
int result1 = a + b; // -2147483648，无任何提示
// 安全加法（溢出时抛出异常）
try {
int result2 = Math.addExact(a, b); // 抛出 ArithmeticException
} catch (ArithmeticException e) {
System.out.println("溢出！" + e.getMessage());
}
// 其他安全方法
Math.subtractExact(a, b); // 安全减法
Math.multiplyExact(a, b); // 安全乘法
Math.negateExact(a); // 安全取负
Math.incrementExact(a); // 安全自增
Math.decrementExact(a); // 安全自减
}
}
三、浮点类型详解
3.1 IEEE 754 标准
<mxfile>
<diagram id="ieee754-float" name="IEEE 754 浮点数表示">
<mxGraphModel dx="1307" dy="1153" grid="1" gridSize="10" guides="1" tooltips="1" connect="1" arrows="1" fold="1" page="1" pageScale="1" pageWidth="900" pageHeight="750" math="0" shadow="0">
<root>
<mxCell id="0" />
<mxCell id="1" parent="0" />
<mxCell id="2" parent="1" style="text;html=1;strokeColor=none;fillColor=none;align=center;verticalAlign=middle;whiteSpace=wrap;rounded=0;fontSize=22;fontStyle=1;fontColor=#1a237e;" value="IEEE 754 浮点数表示" vertex="1">
<mxGeometry height="40" width="500" x="200" y="20" as="geometry" />
</mxCell>
<mxCell id="3" parent="1" style="rounded=1;whiteSpace=wrap;html=1;fillColor=#e8eaf6;strokeColor=#5c6bc0;strokeWidth=2;" value="" vertex="1">
<mxGeometry height="50" width="700" x="100" y="70" as="geometry" />
</mxCell>
<mxCell id="4" parent="1" style="text;html=1;strokeColor=none;fillColor=none;align=center;verticalAlign=middle;whiteSpace=wrap;rounded=0;fontSize=16;fontStyle=1;" value="浮点数 = <font color="#c62828">(-1)<sup>符号位</sup></font> × <font color="#2e7d32">1.尾数</font> × <font color="#1565c0">2<sup>(指数-偏移量)</sup></font>" vertex="1">
<mxGeometry height="50" width="700" x="100" y="70" as="geometry" />
</mxCell>
<mxCell id="5" parent="1" style="text;html=1;strokeColor=none;fillColor=none;align=left;verticalAlign=middle;whiteSpace=wrap;rounded=0;fontSize=16;fontStyle=1;fontColor=#e65100;" value="float (32 位)" vertex="1">
<mxGeometry height="30" width="150" x="140" y="140" as="geometry" />
</mxCell>
<mxCell id="6" parent="1" style="rounded=0;whiteSpace=wrap;html=1;fillColor=#ffcdd2;strokeColor=#c62828;strokeWidth=2;" value="" vertex="1">
<mxGeometry height="60" width="50" x="140" y="175" as="geometry" />
</mxCell>
<mxCell id="7" parent="1" style="text;html=1;strokeColor=none;fillColor=none;align=center;verticalAlign=middle;whiteSpace=wrap;rounded=0;fontSize=12;" value="<b>S</b><br>1位" vertex="1">
<mxGeometry height="60" width="50" x="140" y="175" as="geometry" />
</mxCell>
<mxCell id="8" parent="1" style="text;html=1;strokeColor=none;fillColor=none;align=center;verticalAlign=middle;fontSize=10;fontColor=#c62828;" value="符号" vertex="1">
<mxGeometry height="20" width="50" x="140" y="235" as="geometry" />
</mxCell>
<mxCell id="9" parent="1" style="rounded=0;whiteSpace=wrap;html=1;fillColor=#c8e6c9;strokeColor=#388e3c;strokeWidth=2;" value="" vertex="1">
<mxGeometry height="60" width="150" x="195" y="175" as="geometry" />
</mxCell>
<mxCell id="10" parent="1" style="text;html=1;strokeColor=none;fillColor=none;align=center;verticalAlign=middle;whiteSpace=wrap;rounded=0;fontSize=12;" value="<b>Exponent</b><br>8 位" vertex="1">
<mxGeometry height="60" width="150" x="195" y="175" as="geometry" />
</mxCell>
<mxCell id="11" parent="1" style="text;html=1;strokeColor=none;fillColor=none;align=center;verticalAlign=middle;fontSize=10;fontColor=#388e3c;" value="指数 (偏移127)" vertex="1">
<mxGeometry height="20" width="150" x="195" y="235" as="geometry" />
</mxCell>
<mxCell id="12" parent="1" style="rounded=0;whiteSpace=wrap;html=1;fillColor=#bbdefb;strokeColor=#1976d2;strokeWidth=2;" value="" vertex="1">
<mxGeometry height="60" width="350" x="350" y="175" as="geometry" />
</mxCell>
<mxCell id="13" parent="1" style="text;html=1;strokeColor=none;fillColor=none;align=center;verticalAlign=middle;whiteSpace=wrap;rounded=0;fontSize=12;" value="<b>Mantissa</b><br>23 位" vertex="1">
<mxGeometry height="60" width="350" x="350" y="175" as="geometry" />
</mxCell>
<mxCell id="14" parent="1" style="text;html=1;strokeColor=none;fillColor=none;align=center;verticalAlign=middle;fontSize=10;fontColor=#1976d2;" value="尾数" vertex="1">
<mxGeometry height="20" width="100" x="475" y="235" as="geometry" />
</mxCell>
<mxCell id="15" parent="1" style="text;html=1;strokeColor=none;fillColor=none;align=center;verticalAlign=middle;fontSize=11;fontStyle=2;fontColor=#666666;" value="32位" vertex="1">
<mxGeometry height="30" width="40" x="720" y="190" as="geometry" />
</mxCell>
<mxCell id="16" edge="1" parent="1" style="endArrow=none;html=1;strokeColor=#666666;strokeWidth=1;" value="">
<mxGeometry height="50" relative="1" width="50" as="geometry">
<mxPoint x="710" y="175" as="sourcePoint" />
<mxPoint x="710" y="235" as="targetPoint" />
</mxGeometry>
</mxCell>
<mxCell id="17" parent="1" style="text;html=1;strokeColor=none;fillColor=none;align=left;verticalAlign=middle;whiteSpace=wrap;rounded=0;fontSize=16;fontStyle=1;fontColor=#6a1b9a;" value="double (64 位)" vertex="1">
<mxGeometry height="30" width="150" x="140" y="270" as="geometry" />
</mxCell>
<mxCell id="18" parent="1" style="rounded=0;whiteSpace=wrap;html=1;fillColor=#f3e5f5;strokeColor=#7b1fa2;strokeWidth=2;" value="" vertex="1">
<mxGeometry height="60" width="50" x="140" y="305" as="geometry" />
</mxCell>
<mxCell id="19" parent="1" style="text;html=1;strokeColor=none;fillColor=none;align=center;verticalAlign=middle;whiteSpace=wrap;rounded=0;fontSize=12;" value="<b>S</b><br>1位" vertex="1">
<mxGeometry height="60" width="50" x="140" y="305" as="geometry" />
</mxCell>
<mxCell id="20" parent="1" style="text;html=1;strokeColor=none;fillColor=none;align=center;verticalAlign=middle;fontSize=10;fontColor=#7b1fa2;" value="符号" vertex="1">
<mxGeometry height="20" width="50" x="140" y="365" as="geometry" />
</mxCell>
<mxCell id="21" parent="1" style="rounded=0;whiteSpace=wrap;html=1;fillColor=#dcedc8;strokeColor=#689f38;strokeWidth=2;" value="" vertex="1">
<mxGeometry height="60" width="180" x="195" y="305" as="geometry" />
</mxCell>
<mxCell id="22" parent="1" style="text;html=1;strokeColor=none;fillColor=none;align=center;verticalAlign=middle;whiteSpace=wrap;rounded=0;fontSize=12;" value="<b>Exponent</b><br>11 位" vertex="1">
<mxGeometry height="60" width="180" x="195" y="305" as="geometry" />
</mxCell>
<mxCell id="23" parent="1" style="text;html=1;strokeColor=none;fillColor=none;align=center;verticalAlign=middle;fontSize=10;fontColor=#689f38;" value="指数 (偏移1023)" vertex="1">
<mxGeometry height="20" width="180" x="195" y="365" as="geometry" />
</mxCell>
<mxCell id="24" parent="1" style="rounded=0;whiteSpace=wrap;html=1;fillColor=#e1f5fe;strokeColor=#0288d1;strokeWidth=2;" value="" vertex="1">
<mxGeometry height="60" width="320" x="380" y="305" as="geometry" />
</mxCell>
<mxCell id="25" parent="1" style="text;html=1;strokeColor=none;fillColor=none;align=center;verticalAlign=middle;whiteSpace=wrap;rounded=0;fontSize=12;" value="<b>Mantissa</b><br>52 位" vertex="1">
<mxGeometry height="60" width="320" x="380" y="305" as="geometry" />
</mxCell>
<mxCell id="26" parent="1" style="text;html=1;strokeColor=none;fillColor=none;align=center;verticalAlign=middle;fontSize=10;fontColor=#0288d1;" value="尾数" vertex="1">
<mxGeometry height="20" width="100" x="490" y="365" as="geometry" />
</mxCell>
<mxCell id="27" parent="1" style="text;html=1;strokeColor=none;fillColor=none;align=center;verticalAlign=middle;fontSize=11;fontStyle=2;fontColor=#666666;" value="64位" vertex="1">
<mxGeometry height="30" width="40" x="720" y="320" as="geometry" />
</mxCell>
<mxCell id="28" edge="1" parent="1" style="endArrow=none;html=1;strokeColor=#666666;strokeWidth=1;" value="">
<mxGeometry height="50" relative="1" width="50" as="geometry">
<mxPoint x="710" y="305" as="sourcePoint" />
<mxPoint x="710" y="365" as="targetPoint" />
</mxGeometry>
</mxCell>
<mxCell id="29" parent="1" style="text;html=1;strokeColor=none;fillColor=none;align=left;verticalAlign=middle;whiteSpace=wrap;rounded=0;fontSize=16;fontStyle=1;fontColor=#00695c;" value="📝 示例：float 表示 6.5" vertex="1">
<mxGeometry height="30" width="250" x="100" y="405" as="geometry" />
</mxCell>
<mxCell id="30" parent="1" style="rounded=1;whiteSpace=wrap;html=1;fillColor=#e0f2f1;strokeColor=#00897b;strokeWidth=2;" value="" vertex="1">
<mxGeometry height="280" width="700" x="100" y="440" as="geometry" />
</mxCell>
<mxCell id="31" parent="1" style="rounded=1;whiteSpace=wrap;html=1;fillColor=#ffffff;strokeColor=#26a69a;" value="" vertex="1">
<mxGeometry height="55" width="300" x="120" y="455" as="geometry" />
</mxCell>
<mxCell id="32" parent="1" style="text;html=1;strokeColor=none;fillColor=none;align=center;verticalAlign=middle;whiteSpace=wrap;rounded=0;fontSize=12;" value="<b>Step 1: 十进制转二进制</b><br>6.5 = <font face="Courier New">110.1</font> (二进制)" vertex="1">
<mxGeometry height="55" width="300" x="120" y="455" as="geometry" />
</mxCell>
<mxCell id="33" edge="1" parent="1" style="endArrow=classic;html=1;strokeColor=#00897b;strokeWidth=2;" value="">
<mxGeometry height="50" relative="1" width="50" as="geometry">
<mxPoint x="425" y="482" as="sourcePoint" />
<mxPoint x="475" y="482" as="targetPoint" />
</mxGeometry>
</mxCell>
<mxCell id="34" parent="1" style="rounded=1;whiteSpace=wrap;html=1;fillColor=#ffffff;strokeColor=#26a69a;" value="" vertex="1">
<mxGeometry height="55" width="300" x="480" y="455" as="geometry" />
</mxCell>
<mxCell id="35" parent="1" style="text;html=1;strokeColor=none;fillColor=none;align=center;verticalAlign=middle;whiteSpace=wrap;rounded=0;fontSize=12;" value="<b>Step 2: 规格化</b><br><font face="Courier New">110.1</font> = <font face="Courier New">1.101</font> × 2²" vertex="1">
<mxGeometry height="55" width="300" x="480" y="455" as="geometry" />
</mxCell>
<mxCell id="36" parent="1" style="rounded=1;whiteSpace=wrap;html=1;fillColor=#ffcdd2;strokeColor=#e57373;" value="" vertex="1">
<mxGeometry height="50" width="200" x="120" y="525" as="geometry" />
</mxCell>
<mxCell id="37" parent="1" style="text;html=1;strokeColor=none;fillColor=none;align=center;verticalAlign=middle;whiteSpace=wrap;rounded=0;fontSize=12;" value="<b>符号位</b>: <font face="Courier New" color="#c62828">0</font> (正数)" vertex="1">
<mxGeometry height="50" width="200" x="120" y="525" as="geometry" />
</mxCell>
<mxCell id="38" parent="1" style="rounded=1;whiteSpace=wrap;html=1;fillColor=#c8e6c9;strokeColor=#81c784;" value="" vertex="1">
<mxGeometry height="50" width="200" x="340" y="525" as="geometry" />
</mxCell>
<mxCell id="39" parent="1" style="text;html=1;strokeColor=none;fillColor=none;align=center;verticalAlign=middle;whiteSpace=wrap;rounded=0;fontSize=12;" value="<b>指数</b>: 2 + 127 = 129<br>= <font face="Courier New" color="#388e3c">1000 0001</font>" vertex="1">
<mxGeometry height="50" width="200" x="340" y="525" as="geometry" />
</mxCell>
<mxCell id="40" parent="1" style="rounded=1;whiteSpace=wrap;html=1;fillColor=#bbdefb;strokeColor=#64b5f6;" value="" vertex="1">
<mxGeometry height="50" width="220" x="560" y="525" as="geometry" />
</mxCell>
<mxCell id="41" parent="1" style="text;html=1;strokeColor=none;fillColor=none;align=center;verticalAlign=middle;whiteSpace=wrap;rounded=0;fontSize=12;" value="<b>尾数</b> (省略前导1):<br><font face="Courier New" color="#1976d2">101 0000...0000</font> (23位)" vertex="1">
<mxGeometry height="50" width="220" x="560" y="525" as="geometry" />
</mxCell>
<mxCell id="42" parent="1" style="text;html=1;strokeColor=none;fillColor=none;align=left;verticalAlign=middle;whiteSpace=wrap;rounded=0;fontSize=13;fontStyle=1;fontColor=#00695c;" value="完整的 32 位表示:" vertex="1">
<mxGeometry height="25" width="150" x="120" y="590" as="geometry" />
</mxCell>
<mxCell id="43" parent="1" style="rounded=0;whiteSpace=wrap;html=1;fillColor=#ffcdd2;strokeColor=#c62828;strokeWidth=2;" value="" vertex="1">
<mxGeometry height="45" width="40" x="120" y="620" as="geometry" />
</mxCell>
<mxCell id="44" parent="1" style="text;html=1;strokeColor=none;fillColor=none;align=center;verticalAlign=middle;whiteSpace=wrap;rounded=0;fontSize=14;" value="<font face="Courier New"><b>0</b></font>" vertex="1">
<mxGeometry height="45" width="40" x="120" y="620" as="geometry" />
</mxCell>
<mxCell id="45" parent="1" style="rounded=0;whiteSpace=wrap;html=1;fillColor=#c8e6c9;strokeColor=#388e3c;strokeWidth=2;" value="" vertex="1">
<mxGeometry height="45" width="150" x="165" y="620" as="geometry" />
</mxCell>
<mxCell id="46" parent="1" style="text;html=1;strokeColor=none;fillColor=none;align=center;verticalAlign=middle;whiteSpace=wrap;rounded=0;fontSize=14;" value="<font face="Courier New"><b>10000001</b></font>" vertex="1">
<mxGeometry height="45" width="150" x="165" y="620" as="geometry" />
</mxCell>
<mxCell id="47" parent="1" style="rounded=0;whiteSpace=wrap;html=1;fillColor=#bbdefb;strokeColor=#1976d2;strokeWidth=2;" value="" vertex="1">
<mxGeometry height="45" width="460" x="320" y="620" as="geometry" />
</mxCell>
<mxCell id="48" parent="1" style="text;html=1;strokeColor=none;fillColor=none;align=center;verticalAlign=middle;whiteSpace=wrap;rounded=0;fontSize=14;" value="<font face="Courier New"><b>10100000000000000000000</b></font>" vertex="1">
<mxGeometry height="45" width="460" x="320" y="620" as="geometry" />
</mxCell>
<mxCell id="49" parent="1" style="text;html=1;strokeColor=none;fillColor=none;align=center;verticalAlign=middle;fontSize=9;fontColor=#c62828;" value="1位" vertex="1">
<mxGeometry height="20" width="40" x="120" y="665" as="geometry" />
</mxCell>
<mxCell id="50" parent="1" style="text;html=1;strokeColor=none;fillColor=none;align=center;verticalAlign=middle;fontSize=9;fontColor=#388e3c;" value="8位" vertex="1">
<mxGeometry height="20" width="80" x="200" y="665" as="geometry" />
</mxCell>
<mxCell id="51" parent="1" style="text;html=1;strokeColor=none;fillColor=none;align=center;verticalAlign=middle;fontSize=9;fontColor=#1976d2;" value="23位" vertex="1">
<mxGeometry height="20" width="100" x="500" y="665" as="geometry" />
</mxCell>
<mxCell id="52" parent="1" style="text;html=1;strokeColor=none;fillColor=none;align=left;verticalAlign=middle;whiteSpace=wrap;rounded=0;fontSize=12;" value="十六进制: <font face="Courier New" color="#6a1b9a"><b>0x40D00000</b></font>" vertex="1">
<mxGeometry height="25" width="250" x="120" y="690" as="geometry" />
</mxCell>
</root>
</mxGraphModel>
</diagram>
</mxfile>
3.2 浮点数精度问题
public class FloatPrecisionDemo {
public static void main(String[] args) {
// ═══════════════════════════════════════════════════════════════
// 经典问题：0.1 + 0.2 ≠ 0.3
// ═══════════════════════════════════════════════════════════════
double a = 0.1;
double b = 0.2;
double c = 0.3;
System.out.println("0.1 + 0.2 = " + (a + b)); // 0.30000000000000004
System.out.println("0.1 + 0.2 == 0.3 ? " + (a + b == c)); // false
// ═══════════════════════════════════════════════════════════════
// 另一个例子
// ═══════════════════════════════════════════════════════════════
float f1 = 0.3f - 0.2f; // 0.100000024
float f2 = 0.2f - 0.1f; // 0.099999905
System.out.println("f1 = " + f1);
System.out.println("f2 = " + f2);
System.out.println("f1 == f2 ? " + (f1 == f2)); // false
}
}
<mxfile>
<diagram id="float-precision" name="为什么0.1+0.2≠0.3">
<mxGraphModel dx="1068" dy="484" grid="1" gridSize="10" guides="1" tooltips="1" connect="1" arrows="1" fold="1" page="1" pageScale="1" pageWidth="900" pageHeight="750" math="0" shadow="0">
<root>
<mxCell id="0" />
<mxCell id="1" parent="0" />
<mxCell id="2" parent="1" style="text;html=1;strokeColor=none;fillColor=none;align=center;verticalAlign=middle;fontSize=26;fontStyle=1;fontColor=#1E293B;" value="为什么 0.1 + 0.2 ≠ 0.3 ？" vertex="1">
<mxGeometry height="45" width="450" x="225" y="15" as="geometry" />
</mxCell>
<mxCell id="3" parent="1" style="text;html=1;strokeColor=none;fillColor=#EF4444;align=center;verticalAlign=middle;fontSize=12;fontColor=#FFFFFF;rounded=1;" value="IEEE 754 浮点数精度问题详解" vertex="1">
<mxGeometry height="25" width="250" x="325" y="55" as="geometry" />
</mxCell>
<mxCell id="4" parent="1" style="text;html=1;strokeColor=none;fillColor=#3B82F6;align=center;verticalAlign=middle;fontSize=14;fontStyle=1;fontColor=#FFFFFF;rounded=1;" value="Step 1: 十进制转二进制" vertex="1">
<mxGeometry height="30" width="180" x="40" y="95" as="geometry" />
</mxCell>
<mxCell id="5" parent="1" style="rounded=1;whiteSpace=wrap;html=1;fillColor=#EFF6FF;strokeColor=#3B82F6;strokeWidth=2;" value="" vertex="1">
<mxGeometry height="250" width="400" x="40" y="135" as="geometry" />
</mxCell>
<mxCell id="6" parent="1" style="text;html=1;strokeColor=none;fillColor=none;align=left;verticalAlign=middle;fontSize=12;fontStyle=1;fontColor=#1E40AF;spacingLeft=5;" value="十进制 0.1 转换为二进制的过程：" vertex="1">
<mxGeometry height="20" width="220" x="50" y="145" as="geometry" />
</mxCell>
<mxCell id="7" parent="1" style="rounded=0;whiteSpace=wrap;html=1;fillColor=#F8FAFC;strokeColor=#CBD5E1;strokeWidth=1;fontSize=11;fontColor=#334155;align=left;spacingLeft=10;" value="<font face="Courier New">0.1 × 2 = 0.2</font>" vertex="1">
<mxGeometry height="24" width="140" x="60" y="170" as="geometry" />
</mxCell>
<mxCell id="8" parent="1" style="text;html=1;strokeColor=none;fillColor=#DBEAFE;align=center;verticalAlign=middle;fontSize=12;fontStyle=1;fontColor=#1E40AF;rounded=1;" value="→ 0" vertex="1">
<mxGeometry height="24" width="40" x="210" y="170" as="geometry" />
</mxCell>
<mxCell id="9" parent="1" style="rounded=0;whiteSpace=wrap;html=1;fillColor=#F8FAFC;strokeColor=#CBD5E1;strokeWidth=1;fontSize=11;fontColor=#334155;align=left;spacingLeft=10;" value="<font face="Courier New">0.2 × 2 = 0.4</font>" vertex="1">
<mxGeometry height="24" width="140" x="60" y="194" as="geometry" />
</mxCell>
<mxCell id="10" parent="1" style="text;html=1;strokeColor=none;fillColor=#DBEAFE;align=center;verticalAlign=middle;fontSize=12;fontStyle=1;fontColor=#1E40AF;rounded=1;" value="→ 0" vertex="1">
<mxGeometry height="24" width="40" x="210" y="194" as="geometry" />
</mxCell>
<mxCell id="11" parent="1" style="rounded=0;whiteSpace=wrap;html=1;fillColor=#F8FAFC;strokeColor=#CBD5E1;strokeWidth=1;fontSize=11;fontColor=#334155;align=left;spacingLeft=10;" value="<font face="Courier New">0.4 × 2 = 0.8</font>" vertex="1">
<mxGeometry height="24" width="140" x="60" y="218" as="geometry" />
</mxCell>
<mxCell id="12" parent="1" style="text;html=1;strokeColor=none;fillColor=#DBEAFE;align=center;verticalAlign=middle;fontSize=12;fontStyle=1;fontColor=#1E40AF;rounded=1;" value="→ 0" vertex="1">
<mxGeometry height="24" width="40" x="210" y="218" as="geometry" />
</mxCell>
<mxCell id="13" parent="1" style="rounded=0;whiteSpace=wrap;html=1;fillColor=#F8FAFC;strokeColor=#CBD5E1;strokeWidth=1;fontSize=11;fontColor=#334155;align=left;spacingLeft=10;" value="<font face="Courier New">0.8 × 2 = 1.6</font>" vertex="1">
<mxGeometry height="24" width="140" x="60" y="242" as="geometry" />
</mxCell>
<mxCell id="14" parent="1" style="text;html=1;strokeColor=none;fillColor=#FEE2E2;align=center;verticalAlign=middle;fontSize=12;fontStyle=1;fontColor=#DC2626;rounded=1;" value="→ 1" vertex="1">
<mxGeometry height="24" width="40" x="210" y="242" as="geometry" />
</mxCell>
<mxCell id="15" parent="1" style="rounded=0;whiteSpace=wrap;html=1;fillColor=#F8FAFC;strokeColor=#CBD5E1;strokeWidth=1;fontSize=11;fontColor=#334155;align=left;spacingLeft=10;" value="<font face="Courier New">0.6 × 2 = 1.2</font>" vertex="1">
<mxGeometry height="24" width="140" x="60" y="266" as="geometry" />
</mxCell>
<mxCell id="16" parent="1" style="text;html=1;strokeColor=none;fillColor=#FEE2E2;align=center;verticalAlign=middle;fontSize=12;fontStyle=1;fontColor=#DC2626;rounded=1;" value="→ 1" vertex="1">
<mxGeometry height="24" width="40" x="210" y="266" as="geometry" />
</mxCell>
<mxCell id="17" parent="1" style="rounded=0;whiteSpace=wrap;html=1;fillColor=#FEF3C7;strokeColor=#F59E0B;strokeWidth=2;fontSize=11;fontColor=#334155;align=left;spacingLeft=10;" value="<font face="Courier New">0.2 × 2 = 0.4</font>" vertex="1">
<mxGeometry height="24" width="140" x="60" y="290" as="geometry" />
</mxCell>
<mxCell id="18" parent="1" style="text;html=1;strokeColor=none;fillColor=#DBEAFE;align=center;verticalAlign=middle;fontSize=12;fontStyle=1;fontColor=#1E40AF;rounded=1;" value="→ 0" vertex="1">
<mxGeometry height="24" width="40" x="210" y="290" as="geometry" />
</mxCell>
<mxCell id="19" parent="1" style="text;html=1;strokeColor=none;fillColor=#F59E0B;align=center;verticalAlign=middle;fontSize=11;fontStyle=1;fontColor=#FFFFFF;rounded=1;" value="← 开始循环!" vertex="1">
<mxGeometry height="24" width="80" x="260" y="290" as="geometry" />
</mxCell>
<mxCell id="20" parent="1" style="text;html=1;strokeColor=none;fillColor=none;align=center;verticalAlign=middle;fontSize=14;fontColor=#64748B;" value="<font face="Courier New">...</font>" vertex="1">
<mxGeometry height="20" width="40" x="60" y="314" as="geometry" />
</mxCell>
<mxCell id="21" parent="1" style="rounded=1;whiteSpace=wrap;html=1;fillColor=#FEF2F2;strokeColor=#EF4444;strokeWidth=2;" value="" vertex="1">
<mxGeometry height="35" width="380" x="50" y="340" as="geometry" />
</mxCell>
<mxCell id="22" parent="1" style="text;html=1;strokeColor=none;fillColor=none;align=center;verticalAlign=middle;fontSize=13;fontColor=#991B1B;" value="0.1₁₀ = <font face="Courier New">0.<b>0001100110011</b>0011...</font>₂" vertex="1">
<mxGeometry height="25" width="300" x="55" y="345" as="geometry" />
</mxCell>
<mxCell id="23" parent="1" style="text;html=1;strokeColor=none;fillColor=#EF4444;align=center;verticalAlign=middle;fontSize=10;fontStyle=1;fontColor=#FFFFFF;rounded=1;" value="无限循环!" vertex="1">
<mxGeometry height="18" width="65" x="345" y="348.5" as="geometry" />
</mxCell>
<mxCell id="24" parent="1" style="text;html=1;strokeColor=none;fillColor=#8B5CF6;align=center;verticalAlign=middle;fontSize=14;fontStyle=1;fontColor=#FFFFFF;rounded=1;" value="Step 2: 存储截断" vertex="1">
<mxGeometry height="30" width="140" x="460" y="95" as="geometry" />
</mxCell>
<mxCell id="25" parent="1" style="rounded=1;whiteSpace=wrap;html=1;fillColor=#FAF5FF;strokeColor=#8B5CF6;strokeWidth=2;" value="" vertex="1">
<mxGeometry height="250" width="400" x="460" y="135" as="geometry" />
</mxCell>
<mxCell id="26" parent="1" style="text;html=1;strokeColor=none;fillColor=none;align=left;verticalAlign=middle;fontSize=12;fontStyle=1;fontColor=#6D28D9;spacingLeft=5;" value="浮点数位数有限，必须截断：" vertex="1">
<mxGeometry height="20" width="200" x="470" y="145" as="geometry" />
</mxCell>
<mxCell id="27" parent="1" style="rounded=1;whiteSpace=wrap;html=1;fillColor=#FFFFFF;strokeColor=#DDD6FE;strokeWidth=1;" value="" vertex="1">
<mxGeometry height="80" width="380" x="470" y="170" as="geometry" />
</mxCell>
<mxCell id="28" parent="1" style="text;html=1;strokeColor=none;fillColor=#8B5CF6;align=center;verticalAlign=middle;fontSize=11;fontStyle=1;fontColor=#FFFFFF;rounded=1;" value="double 类型（64位）" vertex="1">
<mxGeometry height="20" width="120" x="480" y="178" as="geometry" />
</mxCell>
<mxCell id="29" parent="1" style="rounded=0;whiteSpace=wrap;html=1;fillColor=#FEE2E2;strokeColor=#FECACA;strokeWidth=1;fontSize=10;fontStyle=1;fontColor=#991B1B;" value="符号位" vertex="1">
<mxGeometry height="35" width="40" x="480" y="205" as="geometry" />
</mxCell>
<mxCell id="30" parent="1" style="text;html=1;strokeColor=none;fillColor=none;align=center;verticalAlign=middle;fontSize=9;fontColor=#991B1B;" value="1位" vertex="1">
<mxGeometry height="15" width="40" x="480" y="225" as="geometry" />
</mxCell>
<mxCell id="31" parent="1" style="rounded=0;whiteSpace=wrap;html=1;fillColor=#DCFCE7;strokeColor=#BBF7D0;strokeWidth=1;fontSize=10;fontStyle=1;fontColor=#166534;" value="指数部分" vertex="1">
<mxGeometry height="35" width="100" x="520" y="205" as="geometry" />
</mxCell>
<mxCell id="32" parent="1" style="text;html=1;strokeColor=none;fillColor=none;align=center;verticalAlign=middle;fontSize=9;fontColor=#166534;" value="11位" vertex="1">
<mxGeometry height="15" width="100" x="520" y="225" as="geometry" />
</mxCell>
<mxCell id="33" parent="1" style="rounded=0;whiteSpace=wrap;html=1;fillColor=#DBEAFE;strokeColor=#BFDBFE;strokeWidth=1;fontSize=10;fontStyle=1;fontColor=#1E40AF;" value="尾数部分（精度关键）" vertex="1">
<mxGeometry height="35" width="220" x="620" y="205" as="geometry" />
</mxCell>
<mxCell id="34" parent="1" style="text;html=1;strokeColor=none;fillColor=none;align=center;verticalAlign=middle;fontSize=9;fontColor=#1E40AF;" value="52位" vertex="1">
<mxGeometry height="15" width="220" x="620" y="225" as="geometry" />
</mxCell>
<mxCell id="35" parent="1" style="text;html=1;strokeColor=none;fillColor=none;align=left;verticalAlign=middle;fontSize=11;fontStyle=1;fontColor=#6D28D9;spacingLeft=5;" value="实际存储值（近似值）：" vertex="1">
<mxGeometry height="20" width="150" x="470" y="260" as="geometry" />
</mxCell>
<mxCell id="36" parent="1" style="text;html=1;strokeColor=none;fillColor=#F3E8FF;align=right;verticalAlign=middle;fontSize=11;fontStyle=1;fontColor=#7C3AED;rounded=1;spacingRight=5;" value="0.1 ≈" vertex="1">
<mxGeometry height="22" width="45" x="470" y="285" as="geometry" />
</mxCell>
<mxCell id="37" parent="1" style="text;html=1;strokeColor=none;fillColor=#F8FAFC;align=left;verticalAlign=middle;fontSize=10;fontColor=#475569;rounded=1;spacingLeft=5;" value="<font face="Courier New">0.100000000000000005551...</font>" vertex="1">
<mxGeometry height="22" width="320" x="520" y="285" as="geometry" />
</mxCell>
<mxCell id="38" parent="1" style="text;html=1;strokeColor=none;fillColor=#F3E8FF;align=right;verticalAlign=middle;fontSize=11;fontStyle=1;fontColor=#7C3AED;rounded=1;spacingRight=5;" value="0.2 ≈" vertex="1">
<mxGeometry height="22" width="45" x="470" y="312" as="geometry" />
</mxCell>
<mxCell id="39" parent="1" style="text;html=1;strokeColor=none;fillColor=#F8FAFC;align=left;verticalAlign=middle;fontSize=10;fontColor=#475569;rounded=1;spacingLeft=5;" value="<font face="Courier New">0.200000000000000011102...</font>" vertex="1">
<mxGeometry height="22" width="320" x="520" y="312" as="geometry" />
</mxCell>
<mxCell id="40" parent="1" style="text;html=1;strokeColor=none;fillColor=#FEE2E2;align=right;verticalAlign=middle;fontSize=11;fontStyle=1;fontColor=#DC2626;rounded=1;spacingRight=5;" value="相加 ≈" vertex="1">
<mxGeometry height="22" width="45" x="470" y="339" as="geometry" />
</mxCell>
<mxCell id="41" parent="1" style="text;html=1;strokeColor=none;fillColor=#FEF2F2;align=left;verticalAlign=middle;fontSize=10;fontColor=#991B1B;rounded=1;spacingLeft=5;" value="<font face="Courier New">0.300000000000000044408...</font>" vertex="1">
<mxGeometry height="22" width="320" x="520" y="339" as="geometry" />
</mxCell>
<mxCell id="42" parent="1" style="text;html=1;strokeColor=none;fillColor=#EF4444;align=center;verticalAlign=middle;fontSize=14;fontStyle=1;fontColor=#FFFFFF;rounded=1;" value="Step 3: 最终结果" vertex="1">
<mxGeometry height="30" width="140" x="40" y="400" as="geometry" />
</mxCell>
<mxCell id="43" parent="1" style="rounded=1;whiteSpace=wrap;html=1;fillColor=#FEF2F2;strokeColor=#EF4444;strokeWidth=2;" value="" vertex="1">
<mxGeometry height="100" width="400" x="40" y="440" as="geometry" />
</mxCell>
<mxCell id="44" parent="1" style="text;html=1;strokeColor=none;fillColor=none;align=left;verticalAlign=middle;fontSize=12;fontStyle=1;fontColor=#991B1B;spacingLeft=5;" value="Java 控制台输出：" vertex="1">
<mxGeometry height="20" width="140" x="50" y="450" as="geometry" />
</mxCell>
<mxCell id="45" parent="1" style="rounded=0;whiteSpace=wrap;html=1;fillColor=#1E293B;strokeColor=#0F172A;strokeWidth=1;fontSize=12;fontColor=#22C55E;align=left;spacingLeft=10;" value="<font face="Courier New">System.out.println(0.1 + 0.2);</font>" vertex="1">
<mxGeometry height="28" width="280" x="50" y="475" as="geometry" />
</mxCell>
<mxCell id="46" parent="1" style="rounded=0;whiteSpace=wrap;html=1;fillColor=#1E293B;strokeColor=#0F172A;strokeWidth=1;fontSize=12;fontColor=#F59E0B;align=left;spacingLeft=10;" value="<font face="Courier New">// 输出: <b>0.30000000000000004</b></font>" vertex="1">
<mxGeometry height="28" width="280" x="50" y="503" as="geometry" />
</mxCell>
<mxCell id="47" parent="1" style="text;html=1;strokeColor=none;fillColor=#EF4444;align=center;verticalAlign=middle;fontSize=18;fontStyle=1;fontColor=#FFFFFF;rounded=1;" value="≠ 0.3" vertex="1">
<mxGeometry height="35" width="80" x="345" y="485" as="geometry" />
</mxCell>
<mxCell id="48" parent="1" style="text;html=1;strokeColor=none;fillColor=#F59E0B;align=center;verticalAlign=middle;fontSize=14;fontStyle=1;fontColor=#FFFFFF;rounded=1;" value="这不是 Bug！" vertex="1">
<mxGeometry height="30" width="120" x="460" y="400" as="geometry" />
</mxCell>
<mxCell id="49" parent="1" style="rounded=1;whiteSpace=wrap;html=1;fillColor=#FFFBEB;strokeColor=#F59E0B;strokeWidth=2;" value="" vertex="1">
<mxGeometry height="100" width="400" x="460" y="440" as="geometry" />
</mxCell>
<mxCell id="50" parent="1" style="text;html=1;strokeColor=none;fillColor=none;align=left;verticalAlign=middle;fontSize=12;fontStyle=1;fontColor=#92400E;spacingLeft=5;" value="⚠️ IEEE 754 标准的固有限制" vertex="1">
<mxGeometry height="20" width="220" x="470" y="450" as="geometry" />
</mxCell>
<mxCell id="51" parent="1" style="text;html=1;strokeColor=none;fillColor=none;align=left;verticalAlign=middle;fontSize=11;fontColor=#78350F;spacingLeft=5;" value="所有遵循此标准的语言都有这个问题：" vertex="1">
<mxGeometry height="20" width="250" x="470" y="475" as="geometry" />
</mxCell>
<mxCell id="52" parent="1" style="rounded=1;whiteSpace=wrap;html=1;fillColor=#EF4444;strokeColor=#DC2626;strokeWidth=1;fontSize=11;fontStyle=1;fontColor=#FFFFFF;" value="Java" vertex="1">
<mxGeometry height="25" width="50" x="480" y="500" as="geometry" />
</mxCell>
<mxCell id="53" parent="1" style="rounded=1;whiteSpace=wrap;html=1;fillColor=#3B82F6;strokeColor=#2563EB;strokeWidth=1;fontSize=11;fontStyle=1;fontColor=#FFFFFF;" value="C/C++" vertex="1">
<mxGeometry height="25" width="55" x="540" y="500" as="geometry" />
</mxCell>
<mxCell id="54" parent="1" style="rounded=1;whiteSpace=wrap;html=1;fillColor=#F59E0B;strokeColor=#D97706;strokeWidth=1;fontSize=11;fontStyle=1;fontColor=#FFFFFF;" value="JavaScript" vertex="1">
<mxGeometry height="25" width="75" x="605" y="500" as="geometry" />
</mxCell>
<mxCell id="55" parent="1" style="rounded=1;whiteSpace=wrap;html=1;fillColor=#22C55E;strokeColor=#16A34A;strokeWidth=1;fontSize=11;fontStyle=1;fontColor=#FFFFFF;" value="Python" vertex="1">
<mxGeometry height="25" width="55" x="690" y="500" as="geometry" />
</mxCell>
<mxCell id="56" parent="1" style="text;html=1;strokeColor=none;fillColor=none;align=center;verticalAlign=middle;fontSize=14;fontStyle=1;fontColor=#78350F;" value="..." vertex="1">
<mxGeometry height="25" width="30" x="755" y="500" as="geometry" />
</mxCell>
<mxCell id="57" parent="1" style="text;html=1;strokeColor=none;fillColor=#22C55E;align=center;verticalAlign=middle;fontSize=14;fontStyle=1;fontColor=#FFFFFF;rounded=1;" value="解决方案" vertex="1">
<mxGeometry height="30" width="100" x="40" y="555" as="geometry" />
</mxCell>
<mxCell id="58" parent="1" style="rounded=1;whiteSpace=wrap;html=1;fillColor=#F0FDF4;strokeColor=#22C55E;strokeWidth=2;" value="" vertex="1">
<mxGeometry height="90" width="820" x="40" y="595" as="geometry" />
</mxCell>
<mxCell id="59" parent="1" style="rounded=1;whiteSpace=wrap;html=1;fillColor=#22C55E;strokeColor=#16A34A;strokeWidth=1;fontSize=12;fontStyle=1;fontColor=#FFFFFF;" value="1. 使用 BigDecimal" vertex="1">
<mxGeometry height="25" width="140" x="55" y="610" as="geometry" />
</mxCell>
<mxCell id="60" parent="1" style="rounded=0;whiteSpace=wrap;html=1;fillColor=#F8FAFC;strokeColor=#CBD5E1;strokeWidth=1;fontSize=10;fontColor=#334155;align=left;spacingLeft=5;" value="<font face="Courier New">new BigDecimal("0.1").add(new BigDecimal("0.2"))</font>" vertex="1">
<mxGeometry height="25" width="340" x="54" y="643" as="geometry" />
</mxCell>
<mxCell id="61" parent="1" style="rounded=1;whiteSpace=wrap;html=1;fillColor=#3B82F6;strokeColor=#2563EB;strokeWidth=1;fontSize=12;fontStyle=1;fontColor=#FFFFFF;" value="2. 误差容忍比较" vertex="1">
<mxGeometry height="25" width="130" x="420" y="610" as="geometry" />
</mxCell>
<mxCell id="62" parent="1" style="rounded=0;whiteSpace=wrap;html=1;fillColor=#F8FAFC;strokeColor=#CBD5E1;strokeWidth=1;fontSize=10;fontColor=#334155;align=left;spacingLeft=5;" value="<font face="Courier New">Math.abs(a - b) &lt; 1e-10</font>" vertex="1">
<mxGeometry height="25" width="180" x="419" y="643" as="geometry" />
</mxCell>
<mxCell id="63" parent="1" style="rounded=1;whiteSpace=wrap;html=1;fillColor=#8B5CF6;strokeColor=#7C3AED;strokeWidth=1;fontSize=12;fontStyle=1;fontColor=#FFFFFF;" value="3. 整数运算" vertex="1">
<mxGeometry height="25" width="100" x="625" y="610" as="geometry" />
</mxCell>
<mxCell id="64" parent="1" style="rounded=0;whiteSpace=wrap;html=1;fillColor=#F8FAFC;strokeColor=#CBD5E1;strokeWidth=1;fontSize=10;fontColor=#334155;align=left;spacingLeft=5;" value="<font face="Courier New">用分表示: 10 + 20 = 30</font>" vertex="1">
<mxGeometry height="25" width="180" x="624" y="643" as="geometry" />
</mxCell>
<mxCell id="65" parent="1" style="text;html=1;strokeColor=none;fillColor=none;align=center;verticalAlign=middle;fontSize=20;" value="💡" vertex="1">
<mxGeometry height="30" width="30" x="810" y="605" as="geometry" />
</mxCell>
<mxCell id="66" edge="1" parent="1" source="23" style="edgeStyle=orthogonalEdgeStyle;rounded=0;orthogonalLoop=1;jettySize=auto;html=1;exitX=0.5;exitY=1;exitDx=0;exitDy=0;" target="23">
<mxGeometry relative="1" as="geometry" />
</mxCell>
</root>
</mxGraphModel>
</diagram>
</mxfile>
3.3 特殊浮点值
public class SpecialFloatDemo {
public static void main(String[] args) {
// 正无穷大
double posInf = Double.POSITIVE_INFINITY;
System.out.println("1.0 / 0.0 = " + (1.0 / 0.0)); // Infinity
System.out.println("Max * 2 = " + (Double.MAX_VALUE * 2)); // Infinity
// 负无穷大
double negInf = Double.NEGATIVE_INFINITY;
System.out.println("-1.0 / 0.0 = " + (-1.0 / 0.0)); // -Infinity
// NaN (Not a Number)
double nan = Double.NaN;
System.out.println("0.0 / 0.0 = " + (0.0 / 0.0)); // NaN
System.out.println("sqrt(-1) = " + Math.sqrt(-1)); // NaN
// NaN 的特殊性质
System.out.println("NaN == NaN ? " + (nan == nan)); // false！
System.out.println("NaN != NaN ? " + (nan != nan)); // true！
// 正确判断 NaN
System.out.println("isNaN ? " + Double.isNaN(nan)); // true
// 判断无穷大
System.out.println("isInfinite ? " + Double.isInfinite(posInf)); // true
System.out.println("isFinite ? " + Double.isFinite(1.0)); // true
}
}
<mxfile>
<diagram id="special-float-values" name="特殊浮点值对比">
<mxGraphModel dx="926" dy="817" grid="1" gridSize="10" guides="1" tooltips="1" connect="1" arrows="1" fold="1" page="1" pageScale="1" pageWidth="900" pageHeight="680" math="0" shadow="0">
<root>
<mxCell id="0" />
<mxCell id="1" parent="0" />
<mxCell id="2" parent="1" style="text;html=1;strokeColor=none;fillColor=none;align=center;verticalAlign=middle;whiteSpace=wrap;rounded=0;fontSize=24;fontStyle=1;fontColor=#1a237e;" value="特殊浮点值对比" vertex="1">
<mxGeometry height="45" width="400" x="250" y="25" as="geometry" />
</mxCell>
<mxCell id="3" parent="1" style="rounded=1;whiteSpace=wrap;html=1;fillColor=#fafafa;strokeColor=#5c6bc0;strokeWidth=2;shadow=1;" value="" vertex="1">
<mxGeometry height="360" width="790" x="50" y="70" as="geometry" />
</mxCell>
<mxCell id="4" parent="1" style="rounded=0;whiteSpace=wrap;html=1;fillColor=#3949ab;strokeColor=none;" value="" vertex="1">
<mxGeometry height="50" width="740" x="80" y="85" as="geometry" />
</mxCell>
<mxCell id="5" parent="1" style="text;html=1;strokeColor=none;fillColor=none;align=center;verticalAlign=middle;whiteSpace=wrap;rounded=0;fontSize=16;fontStyle=1;fontColor=#ffffff;" value="值" vertex="1">
<mxGeometry height="50" width="180" x="80" y="85" as="geometry" />
</mxCell>
<mxCell id="6" parent="1" style="text;html=1;strokeColor=none;fillColor=none;align=center;verticalAlign=middle;whiteSpace=wrap;rounded=0;fontSize=16;fontStyle=1;fontColor=#ffffff;" value="产生条件" vertex="1">
<mxGeometry height="50" width="560" x="260" y="85" as="geometry" />
</mxCell>
<mxCell id="7" parent="1" style="line;strokeWidth=2;html=1;strokeColor=#5c6bc0;" value="" vertex="1">
<mxGeometry height="1" width="740" x="80" y="135" as="geometry" />
</mxCell>
<mxCell id="8" edge="1" parent="1" style="endArrow=none;html=1;strokeColor=#e0e0e0;strokeWidth=2;" value="">
<mxGeometry height="50" relative="1" width="50" as="geometry">
<mxPoint x="260" y="135" as="sourcePoint" />
<mxPoint x="260" y="425" as="targetPoint" />
</mxGeometry>
</mxCell>
<mxCell id="9" parent="1" style="rounded=0;whiteSpace=wrap;html=1;fillColor=#e3f2fd;strokeColor=none;" value="" vertex="1">
<mxGeometry height="70" width="740" x="80" y="136" as="geometry" />
</mxCell>
<mxCell id="10" parent="1" style="rounded=1;whiteSpace=wrap;html=1;fillColor=#1976d2;strokeColor=none;" value="" vertex="1">
<mxGeometry height="40" width="140" x="100" y="151" as="geometry" />
</mxCell>
<mxCell id="11" parent="1" style="text;html=1;strokeColor=none;fillColor=none;align=center;verticalAlign=middle;whiteSpace=wrap;rounded=0;fontSize=15;fontColor=#ffffff;" value="<font face="Courier New"><b>Infinity</b></font>" vertex="1">
<mxGeometry height="40" width="140" x="100" y="151" as="geometry" />
</mxCell>
<mxCell id="12" parent="1" style="text;html=1;strokeColor=none;fillColor=none;align=left;verticalAlign=middle;whiteSpace=wrap;rounded=0;fontSize=14;" value="<font face="Courier New" color="#1565c0">正数 / 0.0</font>，溢出到正无穷" vertex="1">
<mxGeometry height="70" width="520" x="280" y="136" as="geometry" />
</mxCell>
<mxCell id="13" parent="1" style="text;html=1;strokeColor=none;fillColor=none;align=center;verticalAlign=middle;whiteSpace=wrap;rounded=0;fontSize=24;fontColor=#1976d2;fontStyle=1;" value="∞" vertex="1">
<mxGeometry height="70" width="50" x="750" y="136" as="geometry" />
</mxCell>
<mxCell id="14" parent="1" style="line;strokeWidth=1;html=1;strokeColor=#e0e0e0;" value="" vertex="1">
<mxGeometry height="1" width="740" x="80" y="206" as="geometry" />
</mxCell>
<mxCell id="15" parent="1" style="rounded=0;whiteSpace=wrap;html=1;fillColor=#ffffff;strokeColor=none;" value="" vertex="1">
<mxGeometry height="70" width="740" x="80" y="207" as="geometry" />
</mxCell>
<mxCell id="16" parent="1" style="rounded=1;whiteSpace=wrap;html=1;fillColor=#c62828;strokeColor=none;" value="" vertex="1">
<mxGeometry height="40" width="140" x="100" y="222" as="geometry" />
</mxCell>
<mxCell id="17" parent="1" style="text;html=1;strokeColor=none;fillColor=none;align=center;verticalAlign=middle;whiteSpace=wrap;rounded=0;fontSize=15;fontColor=#ffffff;" value="<font face="Courier New"><b>-Infinity</b></font>" vertex="1">
<mxGeometry height="40" width="140" x="100" y="222" as="geometry" />
</mxCell>
<mxCell id="18" parent="1" style="text;html=1;strokeColor=none;fillColor=none;align=left;verticalAlign=middle;whiteSpace=wrap;rounded=0;fontSize=14;" value="<font face="Courier New" color="#c62828">负数 / 0.0</font>，溢出到负无穷" vertex="1">
<mxGeometry height="70" width="520" x="280" y="207" as="geometry" />
</mxCell>
<mxCell id="19" parent="1" style="text;html=1;strokeColor=none;fillColor=none;align=center;verticalAlign=middle;whiteSpace=wrap;rounded=0;fontSize=24;fontColor=#c62828;fontStyle=1;" value="-∞" vertex="1">
<mxGeometry height="70" width="50" x="750" y="207" as="geometry" />
</mxCell>
<mxCell id="20" parent="1" style="line;strokeWidth=1;html=1;strokeColor=#e0e0e0;" value="" vertex="1">
<mxGeometry height="1" width="740" x="80" y="277" as="geometry" />
</mxCell>
<mxCell id="21" parent="1" style="rounded=0;whiteSpace=wrap;html=1;fillColor=#fff3e0;strokeColor=none;" value="" vertex="1">
<mxGeometry height="70" width="740" x="80" y="278" as="geometry" />
</mxCell>
<mxCell id="22" parent="1" style="rounded=1;whiteSpace=wrap;html=1;fillColor=#ef6c00;strokeColor=none;" value="" vertex="1">
<mxGeometry height="40" width="140" x="100" y="293" as="geometry" />
</mxCell>
<mxCell id="23" parent="1" style="text;html=1;strokeColor=none;fillColor=none;align=center;verticalAlign=middle;whiteSpace=wrap;rounded=0;fontSize=15;fontColor=#ffffff;" value="<font face="Courier New"><b>NaN</b></font>" vertex="1">
<mxGeometry height="40" width="140" x="100" y="293" as="geometry" />
</mxCell>
<mxCell id="24" parent="1" style="text;html=1;strokeColor=none;fillColor=none;align=left;verticalAlign=middle;whiteSpace=wrap;rounded=0;fontSize=14;" value="<font face="Courier New" color="#e65100">0.0 / 0.0</font>，<font face="Courier New" color="#e65100">√负数</font>，无意义运算" vertex="1">
<mxGeometry height="70" width="520" x="280" y="278" as="geometry" />
</mxCell>
<mxCell id="25" parent="1" style="text;html=1;strokeColor=none;fillColor=none;align=center;verticalAlign=middle;whiteSpace=wrap;rounded=0;fontSize=28;fontColor=#ef6c00;fontStyle=1;" value="?" vertex="1">
<mxGeometry height="70" width="50" x="750" y="278" as="geometry" />
</mxCell>
<mxCell id="26" parent="1" style="line;strokeWidth=1;html=1;strokeColor=#e0e0e0;" value="" vertex="1">
<mxGeometry height="1" width="740" x="80" y="348" as="geometry" />
</mxCell>
<mxCell id="27" parent="1" style="rounded=0;whiteSpace=wrap;html=1;fillColor=#f3e5f5;strokeColor=none;" value="" vertex="1">
<mxGeometry height="70" width="740" x="80" y="349" as="geometry" />
</mxCell>
<mxCell id="28" parent="1" style="rounded=1;whiteSpace=wrap;html=1;fillColor=#7b1fa2;strokeColor=none;" value="" vertex="1">
<mxGeometry height="40" width="140" x="100" y="364" as="geometry" />
</mxCell>
<mxCell id="29" parent="1" style="text;html=1;strokeColor=none;fillColor=none;align=center;verticalAlign=middle;whiteSpace=wrap;rounded=0;fontSize=15;fontColor=#ffffff;" value="<font face="Courier New"><b>-0.0</b></font>" vertex="1">
<mxGeometry height="40" width="140" x="100" y="364" as="geometry" />
</mxCell>
<mxCell id="30" parent="1" style="text;html=1;strokeColor=none;fillColor=none;align=left;verticalAlign=middle;whiteSpace=wrap;rounded=0;fontSize=14;" value="负数下溢，与 <font face="Courier New" color="#7b1fa2">+0.0</font> 相等但符号不同" vertex="1">
<mxGeometry height="70" width="520" x="280" y="349" as="geometry" />
</mxCell>
<mxCell id="31" parent="1" style="text;html=1;strokeColor=none;fillColor=none;align=center;verticalAlign=middle;whiteSpace=wrap;rounded=0;fontSize=28;fontColor=#7b1fa2;fontStyle=1;" value="±" vertex="1">
<mxGeometry height="70" width="50" x="750" y="349" as="geometry" />
</mxCell>
<mxCell id="32" parent="1" style="rounded=1;whiteSpace=wrap;html=1;fillColor=#fff8e1;strokeColor=#ffa000;strokeWidth=2;shadow=1;" value="" vertex="1">
<mxGeometry height="100" width="740" x="80" y="445" as="geometry" />
</mxCell>
<mxCell id="33" parent="1" style="text;html=1;strokeColor=none;fillColor=none;align=center;verticalAlign=middle;whiteSpace=wrap;rounded=0;fontSize=32;" value="⚠️" vertex="1">
<mxGeometry height="60" width="60" x="100" y="465" as="geometry" />
</mxCell>
<mxCell id="34" parent="1" style="text;html=1;strokeColor=none;fillColor=none;align=left;verticalAlign=middle;whiteSpace=wrap;rounded=0;fontSize=16;fontStyle=1;fontColor=#e65100;" value="注意" vertex="1">
<mxGeometry height="30" width="60" x="160" y="455" as="geometry" />
</mxCell>
<mxCell id="35" parent="1" style="rounded=1;whiteSpace=wrap;html=1;fillColor=#ffccbc;strokeColor=#ff7043;" value="" vertex="1">
<mxGeometry height="45" width="310" x="160" y="485" as="geometry" />
</mxCell>
<mxCell id="36" parent="1" style="text;html=1;strokeColor=none;fillColor=none;align=center;verticalAlign=middle;whiteSpace=wrap;rounded=0;fontSize=12;" value="<b>整数</b>除以 0 → 抛出 <font face="Courier New" color="#d84315">ArithmeticException</font>" vertex="1">
<mxGeometry height="45" width="310" x="160" y="485" as="geometry" />
</mxCell>
<mxCell id="37" parent="1" style="rounded=1;whiteSpace=wrap;html=1;fillColor=#c8e6c9;strokeColor=#66bb6a;" value="" vertex="1">
<mxGeometry height="45" width="310" x="490" y="485" as="geometry" />
</mxCell>
<mxCell id="38" parent="1" style="text;html=1;strokeColor=none;fillColor=none;align=center;verticalAlign=middle;whiteSpace=wrap;rounded=0;fontSize=12;" value="<b>浮点数</b>除以 0 → 得到 <font face="Courier New" color="#2e7d32">Infinity</font> 或 <font face="Courier New" color="#2e7d32">NaN</font>" vertex="1">
<mxGeometry height="45" width="310" x="490" y="485" as="geometry" />
</mxCell>
<mxCell id="39" parent="1" style="ellipse;whiteSpace=wrap;html=1;fillColor=#5c6bc0;strokeColor=none;fontColor=#ffffff;fontStyle=1;fontSize=11;" value="VS" vertex="1">
<mxGeometry height="25" width="35" x="460" y="495" as="geometry" />
</mxCell>
<mxCell id="40" parent="1" style="text;html=1;strokeColor=none;fillColor=none;align=center;verticalAlign=middle;whiteSpace=wrap;rounded=0;fontSize=12;fontStyle=2;fontColor=#9e9e9e;" value="IEEE 754 标准定义了这些特殊值的表示方式" vertex="1">
<mxGeometry height="25" width="400" x="250" y="560" as="geometry" />
</mxCell>
</root>
</mxGraphModel>
</diagram>
</mxfile>
四、字符类型
4.1 char 类型详解
<mxfile>
<diagram id="char-type" name="char类型详解">
<mxGraphModel dx="1281" dy="581" grid="1" gridSize="10" guides="1" tooltips="1" connect="1" arrows="1" fold="1" page="1" pageScale="1" pageWidth="900" pageHeight="700" math="0" shadow="0">
<root>
<mxCell id="0" />
<mxCell id="1" parent="0" />
<mxCell id="2" parent="1" style="text;html=1;strokeColor=none;fillColor=none;align=center;verticalAlign=middle;fontSize=28;fontStyle=1;fontColor=#1E293B;" value="char 类型" vertex="1">
<mxGeometry height="45" width="250" x="305" y="20" as="geometry" />
</mxCell>
<mxCell id="3" parent="1" style="text;html=1;strokeColor=none;fillColor=#8B5CF6;align=center;verticalAlign=middle;fontSize=12;fontColor=#FFFFFF;rounded=1;" value="Java 字符类型详解" vertex="1">
<mxGeometry height="25" width="170" x="345" y="60" as="geometry" />
</mxCell>
<mxCell id="4" parent="1" style="text;html=1;strokeColor=none;fillColor=#3B82F6;align=center;verticalAlign=middle;fontSize=14;fontStyle=1;fontColor=#FFFFFF;rounded=1;" value="基本特性" vertex="1">
<mxGeometry height="30" width="100" x="40" y="105" as="geometry" />
</mxCell>
<mxCell id="5" parent="1" style="rounded=1;whiteSpace=wrap;html=1;fillColor=#EFF6FF;strokeColor=#3B82F6;strokeWidth=2;" value="" vertex="1">
<mxGeometry height="200" width="380" x="40" y="145" as="geometry" />
</mxCell>
<mxCell id="6" parent="1" style="rounded=1;whiteSpace=wrap;html=1;fillColor=#FFFFFF;strokeColor=#BFDBFE;strokeWidth=1;" value="" vertex="1">
<mxGeometry height="70" width="165" x="55" y="160" as="geometry" />
</mxCell>
<mxCell id="7" parent="1" style="text;html=1;strokeColor=none;fillColor=none;align=center;verticalAlign=middle;fontSize=11;fontStyle=1;fontColor=#1E40AF;" value="📦 存储大小" vertex="1">
<mxGeometry height="20" width="80" x="60" y="165" as="geometry" />
</mxCell>
<mxCell id="8" parent="1" style="text;html=1;strokeColor=none;fillColor=#3B82F6;align=center;verticalAlign=middle;fontSize=18;fontStyle=1;fontColor=#FFFFFF;rounded=1;" value="2 字节" vertex="1">
<mxGeometry height="30" width="70" x="65" y="188" as="geometry" />
</mxCell>
<mxCell id="9" parent="1" style="text;html=1;strokeColor=none;fillColor=#DBEAFE;align=center;verticalAlign=middle;fontSize=12;fontColor=#1E40AF;rounded=1;" value="16 位" vertex="1">
<mxGeometry height="22" width="50" x="145" y="193" as="geometry" />
</mxCell>
<mxCell id="10" parent="1" style="rounded=1;whiteSpace=wrap;html=1;fillColor=#FFFFFF;strokeColor=#BFDBFE;strokeWidth=1;" value="" vertex="1">
<mxGeometry height="70" width="170" x="235" y="160" as="geometry" />
</mxCell>
<mxCell id="11" parent="1" style="text;html=1;strokeColor=none;fillColor=none;align=center;verticalAlign=middle;fontSize=11;fontStyle=1;fontColor=#1E40AF;" value="🌐 编码方式" vertex="1">
<mxGeometry height="20" width="80" x="240" y="165" as="geometry" />
</mxCell>
<mxCell id="12" parent="1" style="text;html=1;strokeColor=none;fillColor=#8B5CF6;align=center;verticalAlign=middle;fontSize=16;fontStyle=1;fontColor=#FFFFFF;rounded=1;" value="Unicode" vertex="1">
<mxGeometry height="30" width="90" x="250" y="188" as="geometry" />
</mxCell>
<mxCell id="13" parent="1" style="text;html=1;strokeColor=none;fillColor=#F3E8FF;align=center;verticalAlign=middle;fontSize=10;fontColor=#7C3AED;rounded=1;" value="UTF-16" vertex="1">
<mxGeometry height="22" width="50" x="345" y="193" as="geometry" />
</mxCell>
<mxCell id="14" parent="1" style="rounded=1;whiteSpace=wrap;html=1;fillColor=#FFFFFF;strokeColor=#BFDBFE;strokeWidth=1;" value="" vertex="1">
<mxGeometry height="85" width="165" x="55" y="245" as="geometry" />
</mxCell>
<mxCell id="15" parent="1" style="text;html=1;strokeColor=none;fillColor=none;align=center;verticalAlign=middle;fontSize=11;fontStyle=1;fontColor=#1E40AF;" value="📊 取值范围" vertex="1">
<mxGeometry height="20" width="80" x="60" y="250" as="geometry" />
</mxCell>
<mxCell id="16" parent="1" style="rounded=0;whiteSpace=wrap;html=1;fillColor=#22C55E;strokeColor=#16A34A;strokeWidth=1;fontSize=14;fontStyle=1;fontColor=#FFFFFF;fontFamily=Courier New;" value="0" vertex="1">
<mxGeometry height="28" width="50" x="65" y="275" as="geometry" />
</mxCell>
<mxCell id="17" parent="1" style="text;html=1;strokeColor=none;fillColor=none;align=center;verticalAlign=middle;fontSize=16;fontStyle=1;fontColor=#64748B;" value="~" vertex="1">
<mxGeometry height="28" width="25" x="115" y="275" as="geometry" />
</mxCell>
<mxCell id="18" parent="1" style="rounded=0;whiteSpace=wrap;html=1;fillColor=#EF4444;strokeColor=#DC2626;strokeWidth=1;fontSize=14;fontStyle=1;fontColor=#FFFFFF;fontFamily=Courier New;" value="65535" vertex="1">
<mxGeometry height="28" width="70" x="140" y="275" as="geometry" />
</mxCell>
<mxCell id="19" parent="1" style="text;html=1;strokeColor=none;fillColor=#FEF3C7;align=center;verticalAlign=middle;fontSize=10;fontStyle=1;fontColor=#92400E;rounded=1;" value="无符号整数" vertex="1">
<mxGeometry height="18" width="70" x="80" y="308" as="geometry" />
</mxCell>
<mxCell id="20" parent="1" style="rounded=1;whiteSpace=wrap;html=1;fillColor=#FFFFFF;strokeColor=#BFDBFE;strokeWidth=1;" value="" vertex="1">
<mxGeometry height="85" width="170" x="235" y="245" as="geometry" />
</mxCell>
<mxCell id="21" parent="1" style="text;html=1;strokeColor=none;fillColor=none;align=center;verticalAlign=middle;fontSize=11;fontStyle=1;fontColor=#1E40AF;" value="🔢 算术运算" vertex="1">
<mxGeometry height="20" width="80" x="240" y="250" as="geometry" />
</mxCell>
<mxCell id="22" parent="1" style="text;html=1;strokeColor=none;fillColor=#22C55E;align=center;verticalAlign=middle;fontSize=12;fontStyle=1;fontColor=#FFFFFF;rounded=1;" value="可参与运算" vertex="1">
<mxGeometry height="25" width="90" x="250" y="275" as="geometry" />
</mxCell>
<mxCell id="23" parent="1" style="text;html=1;strokeColor=none;fillColor=#DCFCE7;align=center;verticalAlign=middle;fontSize=10;fontColor=#166534;rounded=1;" value="自动转为 int" vertex="1">
<mxGeometry height="20" width="80" x="255" y="305" as="geometry" />
</mxCell>
<mxCell id="24" parent="1" style="text;html=1;strokeColor=none;fillColor=#F59E0B;align=center;verticalAlign=middle;fontSize=14;fontStyle=1;fontColor=#FFFFFF;rounded=1;" value="char 的各种表示方式" vertex="1">
<mxGeometry height="30" width="170" x="440" y="105" as="geometry" />
</mxCell>
<mxCell id="25" parent="1" style="rounded=1;whiteSpace=wrap;html=1;fillColor=#FFFBEB;strokeColor=#F59E0B;strokeWidth=2;" value="" vertex="1">
<mxGeometry height="215" width="420" x="440" y="145" as="geometry" />
</mxCell>
<mxCell id="26" parent="1" style="rounded=1;whiteSpace=wrap;html=1;fillColor=#FFFFFF;strokeColor=#FDE68A;strokeWidth=1;" value="" vertex="1">
<mxGeometry height="40" width="390" x="455" y="157" as="geometry" />
</mxCell>
<mxCell id="27" parent="1" style="text;html=1;strokeColor=none;fillColor=#FEF3C7;align=center;verticalAlign=middle;fontSize=16;fontColor=#92400E;rounded=1;" value="<font face="Courier New"><b>'A'</b></font>" vertex="1">
<mxGeometry height="26" width="60" x="465" y="165" as="geometry" />
</mxCell>
<mxCell id="28" parent="1" style="text;html=1;strokeColor=none;fillColor=#F59E0B;align=center;verticalAlign=middle;fontSize=11;fontStyle=1;fontColor=#FFFFFF;rounded=1;" value="字符字面量" vertex="1">
<mxGeometry height="22" width="80" x="540" y="167" as="geometry" />
</mxCell>
<mxCell id="29" parent="1" style="text;html=1;strokeColor=none;fillColor=none;align=left;verticalAlign=middle;fontSize=10;fontColor=#78350F;" value="最常用的方式，直接用单引号包裹字符" vertex="1">
<mxGeometry height="22" width="210" x="630" y="167" as="geometry" />
</mxCell>
<mxCell id="30" parent="1" style="rounded=1;whiteSpace=wrap;html=1;fillColor=#FFFFFF;strokeColor=#FDE68A;strokeWidth=1;" value="" vertex="1">
<mxGeometry height="40" width="390" x="455" y="207" as="geometry" />
</mxCell>
<mxCell id="31" parent="1" style="text;html=1;strokeColor=none;fillColor=#F3E8FF;align=center;verticalAlign=middle;fontSize=14;fontColor=#7C3AED;rounded=1;" value="<font face="Courier New"><b>'\u0041'</b></font>" vertex="1">
<mxGeometry height="26" width="80" x="465" y="215" as="geometry" />
</mxCell>
<mxCell id="32" parent="1" style="text;html=1;strokeColor=none;fillColor=#8B5CF6;align=center;verticalAlign=middle;fontSize=11;fontStyle=1;fontColor=#FFFFFF;rounded=1;" value="Unicode 转义" vertex="1">
<mxGeometry height="22" width="90" x="555" y="217" as="geometry" />
</mxCell>
<mxCell id="33" parent="1" style="text;html=1;strokeColor=none;fillColor=none;align=left;verticalAlign=middle;fontSize=10;fontColor=#78350F;" value="等于 'A'，\u + 4位十六进制" vertex="1">
<mxGeometry height="22" width="180" x="655" y="217" as="geometry" />
</mxCell>
<mxCell id="34" parent="1" style="rounded=1;whiteSpace=wrap;html=1;fillColor=#FFFFFF;strokeColor=#FDE68A;strokeWidth=1;" value="" vertex="1">
<mxGeometry height="40" width="390" x="455" y="257" as="geometry" />
</mxCell>
<mxCell id="35" parent="1" style="text;html=1;strokeColor=none;fillColor=#DBEAFE;align=center;verticalAlign=middle;fontSize=16;fontColor=#1E40AF;rounded=1;" value="<font face="Courier New"><b>65</b></font>" vertex="1">
<mxGeometry height="26" width="60" x="465" y="265" as="geometry" />
</mxCell>
<mxCell id="36" parent="1" style="text;html=1;strokeColor=none;fillColor=#3B82F6;align=center;verticalAlign=middle;fontSize=11;fontStyle=1;fontColor=#FFFFFF;rounded=1;" value="整数值" vertex="1">
<mxGeometry height="22" width="60" x="540" y="267" as="geometry" />
</mxCell>
<mxCell id="37" parent="1" style="text;html=1;strokeColor=none;fillColor=none;align=left;verticalAlign=middle;fontSize=10;fontColor=#78350F;" value="等于 'A'，直接使用 Unicode 码值" vertex="1">
<mxGeometry height="22" width="220" x="610" y="267" as="geometry" />
</mxCell>
<mxCell id="38" parent="1" style="rounded=1;whiteSpace=wrap;html=1;fillColor=#FFFFFF;strokeColor=#FDE68A;strokeWidth=1;" value="" vertex="1">
<mxGeometry height="40" width="390" x="455" y="307" as="geometry" />
</mxCell>
<mxCell id="39" parent="1" style="text;html=1;strokeColor=none;fillColor=#DCFCE7;align=center;verticalAlign=middle;fontSize=16;fontColor=#166534;rounded=1;" value="<font face="Courier New"><b>'\n'</b></font>" vertex="1">
<mxGeometry height="26" width="60" x="465" y="315" as="geometry" />
</mxCell>
<mxCell id="40" parent="1" style="text;html=1;strokeColor=none;fillColor=#22C55E;align=center;verticalAlign=middle;fontSize=11;fontStyle=1;fontColor=#FFFFFF;rounded=1;" value="转义字符" vertex="1">
<mxGeometry height="22" width="70" x="540" y="317" as="geometry" />
</mxCell>
<mxCell id="41" parent="1" style="text;html=1;strokeColor=none;fillColor=none;align=left;verticalAlign=middle;fontSize=10;fontColor=#78350F;" value="换行符，还有 \t \r \\ \' 等" vertex="1">
<mxGeometry height="22" width="200" x="620" y="317" as="geometry" />
</mxCell>
<mxCell id="42" parent="1" style="text;html=1;strokeColor=none;fillColor=#22C55E;align=center;verticalAlign=middle;fontSize=14;fontStyle=1;fontColor=#FFFFFF;rounded=1;" value="常用转义字符" vertex="1">
<mxGeometry height="30" width="120" x="40" y="380" as="geometry" />
</mxCell>
<mxCell id="43" parent="1" style="rounded=1;whiteSpace=wrap;html=1;fillColor=#F0FDF4;strokeColor=#22C55E;strokeWidth=2;" value="" vertex="1">
<mxGeometry height="140" width="380" x="40" y="420" as="geometry" />
</mxCell>
<mxCell id="44" parent="1" style="rounded=0;whiteSpace=wrap;html=1;fillColor=#FFFFFF;strokeColor=#BBF7D0;strokeWidth=1;fontSize=12;fontStyle=1;fontColor=#166534;" value="<font face="Courier New">\n</font>" vertex="1">
<mxGeometry height="28" width="50" x="55" y="435" as="geometry" />
</mxCell>
<mxCell id="45" parent="1" style="text;html=1;strokeColor=none;fillColor=none;align=left;verticalAlign=middle;fontSize=11;fontColor=#166534;" value="换行" vertex="1">
<mxGeometry height="28" width="40" x="115" y="435" as="geometry" />
</mxCell>
<mxCell id="46" parent="1" style="rounded=0;whiteSpace=wrap;html=1;fillColor=#FFFFFF;strokeColor=#BBF7D0;strokeWidth=1;fontSize=12;fontStyle=1;fontColor=#166534;" value="<font face="Courier New">\t</font>" vertex="1">
<mxGeometry height="28" width="50" x="165" y="435" as="geometry" />
</mxCell>
<mxCell id="47" parent="1" style="text;html=1;strokeColor=none;fillColor=none;align=left;verticalAlign=middle;fontSize=11;fontColor=#166534;" value="制表符" vertex="1">
<mxGeometry height="28" width="50" x="225" y="435" as="geometry" />
</mxCell>
<mxCell id="48" parent="1" style="rounded=0;whiteSpace=wrap;html=1;fillColor=#FFFFFF;strokeColor=#BBF7D0;strokeWidth=1;fontSize=12;fontStyle=1;fontColor=#166534;" value="<font face="Courier New">\r</font>" vertex="1">
<mxGeometry height="28" width="50" x="285" y="435" as="geometry" />
</mxCell>
<mxCell id="49" parent="1" style="text;html=1;strokeColor=none;fillColor=none;align=left;verticalAlign=middle;fontSize=11;fontColor=#166534;" value="回车" vertex="1">
<mxGeometry height="28" width="40" x="345" y="435" as="geometry" />
</mxCell>
<mxCell id="50" parent="1" style="rounded=0;whiteSpace=wrap;html=1;fillColor=#FFFFFF;strokeColor=#BBF7D0;strokeWidth=1;fontSize=12;fontStyle=1;fontColor=#166534;" value="<font face="Courier New">\\</font>" vertex="1">
<mxGeometry height="28" width="50" x="55" y="475" as="geometry" />
</mxCell>
<mxCell id="51" parent="1" style="text;html=1;strokeColor=none;fillColor=none;align=left;verticalAlign=middle;fontSize=11;fontColor=#166534;" value="反斜杠" vertex="1">
<mxGeometry height="28" width="50" x="115" y="475" as="geometry" />
</mxCell>
<mxCell id="52" parent="1" style="rounded=0;whiteSpace=wrap;html=1;fillColor=#FFFFFF;strokeColor=#BBF7D0;strokeWidth=1;fontSize=12;fontStyle=1;fontColor=#166534;" value="<font face="Courier New">\'</font>" vertex="1">
<mxGeometry height="28" width="50" x="165" y="475" as="geometry" />
</mxCell>
<mxCell id="53" parent="1" style="text;html=1;strokeColor=none;fillColor=none;align=left;verticalAlign=middle;fontSize=11;fontColor=#166534;" value="单引号" vertex="1">
<mxGeometry height="28" width="50" x="225" y="475" as="geometry" />
</mxCell>
<mxCell id="54" parent="1" style="rounded=0;whiteSpace=wrap;html=1;fillColor=#FFFFFF;strokeColor=#BBF7D0;strokeWidth=1;fontSize=12;fontStyle=1;fontColor=#166534;" value="<font face="Courier New">\"</font>" vertex="1">
<mxGeometry height="28" width="50" x="285" y="475" as="geometry" />
</mxCell>
<mxCell id="55" parent="1" style="text;html=1;strokeColor=none;fillColor=none;align=left;verticalAlign=middle;fontSize=11;fontColor=#166534;" value="双引号" vertex="1">
<mxGeometry height="28" width="50" x="345" y="475" as="geometry" />
</mxCell>
<mxCell id="56" parent="1" style="rounded=0;whiteSpace=wrap;html=1;fillColor=#FFFFFF;strokeColor=#BBF7D0;strokeWidth=1;fontSize=12;fontStyle=1;fontColor=#166534;" value="<font face="Courier New">\0</font>" vertex="1">
<mxGeometry height="28" width="50" x="55" y="515" as="geometry" />
</mxCell>
<mxCell id="57" parent="1" style="text;html=1;strokeColor=none;fillColor=none;align=left;verticalAlign=middle;fontSize=11;fontColor=#166534;" value="空字符" vertex="1">
<mxGeometry height="28" width="50" x="115" y="515" as="geometry" />
</mxCell>
<mxCell id="58" parent="1" style="text;html=1;strokeColor=none;fillColor=#8B5CF6;align=center;verticalAlign=middle;fontSize=14;fontStyle=1;fontColor=#FFFFFF;rounded=1;" value="常用字符码值" vertex="1">
<mxGeometry height="30" width="120" x="440" y="380" as="geometry" />
</mxCell>
<mxCell id="59" parent="1" style="rounded=1;whiteSpace=wrap;html=1;fillColor=#FAF5FF;strokeColor=#8B5CF6;strokeWidth=2;" value="" vertex="1">
<mxGeometry height="140" width="260" x="440" y="420" as="geometry" />
</mxCell>
<mxCell id="60" parent="1" style="text;html=1;strokeColor=none;fillColor=#8B5CF6;align=center;verticalAlign=middle;fontSize=11;fontStyle=1;fontColor=#FFFFFF;rounded=1;" value="字符" vertex="1">
<mxGeometry height="22" width="50" x="455" y="430" as="geometry" />
</mxCell>
<mxCell id="61" parent="1" style="text;html=1;strokeColor=none;fillColor=#8B5CF6;align=center;verticalAlign=middle;fontSize=11;fontStyle=1;fontColor=#FFFFFF;rounded=1;" value="十进制" vertex="1">
<mxGeometry height="22" width="60" x="515" y="430" as="geometry" />
</mxCell>
<mxCell id="62" parent="1" style="text;html=1;strokeColor=none;fillColor=#8B5CF6;align=center;verticalAlign=middle;fontSize=11;fontStyle=1;fontColor=#FFFFFF;rounded=1;" value="说明" vertex="1">
<mxGeometry height="22" width="80" x="585" y="430" as="geometry" />
</mxCell>
<mxCell id="63" parent="1" style="text;html=1;strokeColor=none;fillColor=#F3E8FF;align=center;verticalAlign=middle;fontSize=11;fontFamily=Courier New;fontColor=#7C3AED;rounded=1;" value="'0'-'9'" vertex="1">
<mxGeometry height="24" width="50" x="455" y="460" as="geometry" />
</mxCell>
<mxCell id="64" parent="1" style="text;html=1;strokeColor=none;fillColor=#FFFFFF;align=center;verticalAlign=middle;fontSize=11;fontFamily=Courier New;fontColor=#6D28D9;rounded=1;strokeWidth=1;" value="48-57" vertex="1">
<mxGeometry height="24" width="60" x="515" y="460" as="geometry" />
</mxCell>
<mxCell id="65" parent="1" style="text;html=1;strokeColor=none;fillColor=none;align=center;verticalAlign=middle;fontSize=11;fontColor=#6D28D9;" value="数字字符" vertex="1">
<mxGeometry height="24" width="80" x="585" y="460" as="geometry" />
</mxCell>
<mxCell id="66" parent="1" style="text;html=1;strokeColor=none;fillColor=#DBEAFE;align=center;verticalAlign=middle;fontSize=11;fontFamily=Courier New;fontColor=#1E40AF;rounded=1;" value="'A'-'Z'" vertex="1">
<mxGeometry height="24" width="50" x="455" y="492" as="geometry" />
</mxCell>
<mxCell id="67" parent="1" style="text;html=1;strokeColor=none;fillColor=#FFFFFF;align=center;verticalAlign=middle;fontSize=11;fontFamily=Courier New;fontColor=#1E40AF;rounded=1;strokeWidth=1;" value="65-90" vertex="1">
<mxGeometry height="24" width="60" x="515" y="492" as="geometry" />
</mxCell>
<mxCell id="68" parent="1" style="text;html=1;strokeColor=none;fillColor=none;align=center;verticalAlign=middle;fontSize=11;fontColor=#1E40AF;" value="大写字母" vertex="1">
<mxGeometry height="24" width="80" x="585" y="492" as="geometry" />
</mxCell>
<mxCell id="69" parent="1" style="text;html=1;strokeColor=none;fillColor=#DCFCE7;align=center;verticalAlign=middle;fontSize=11;fontFamily=Courier New;fontColor=#166534;rounded=1;" value="'a'-'z'" vertex="1">
<mxGeometry height="24" width="50" x="455" y="524" as="geometry" />
</mxCell>
<mxCell id="70" parent="1" style="text;html=1;strokeColor=none;fillColor=#FFFFFF;align=center;verticalAlign=middle;fontSize=11;fontFamily=Courier New;fontColor=#166534;rounded=1;strokeWidth=1;" value="97-122" vertex="1">
<mxGeometry height="24" width="60" x="515" y="524" as="geometry" />
</mxCell>
<mxCell id="71" parent="1" style="text;html=1;strokeColor=none;fillColor=none;align=center;verticalAlign=middle;fontSize=11;fontColor=#166534;" value="小写字母" vertex="1">
<mxGeometry height="24" width="80" x="585" y="524" as="geometry" />
</mxCell>
</root>
</mxGraphModel>
</diagram>
</mxfile>
public class CharDemo {
public static void main(String[] args) {
// ═══════════════════════════════════════════════════════════════
// char 的各种写法
// ═══════════════════════════════════════════════════════════════
char c1 = 'A'; // 字符字面量
char c2 = '\u0041'; // Unicode 转义
char c3 = 65; // 整数赋值
char c4 = '\n'; // 转义字符
System.out.println(c1 == c2); // true
System.out.println(c1 == c3); // true
// ═══════════════════════════════════════════════════════════════
// char 参与运算
// ═══════════════════════════════════════════════════════════════
char letter = 'A';
System.out.println(letter + 1); // 66 (int)
System.out.println((char)(letter + 1)); // B
// 大小写转换
char lower = 'a';
char upper = (char)(lower - 32); // 'A'
// 或使用 Character 类
upper = Character.toUpperCase(lower);
// ═══════════════════════════════════════════════════════════════
// 字符判断
// ═══════════════════════════════════════════════════════════════
char ch = '9';
System.out.println(Character.isDigit(ch)); // true
System.out.println(Character.isLetter(ch)); // false
System.out.println(Character.isLetterOrDigit(ch)); // true
System.out.println(Character.isWhitespace(' ')); // true
}
}
4.2 char 与 String 的区别
// ═══════════════════════════════════════════════════════════════════════
// char 与 String 的区别
// ═══════════════════════════════════════════════════════════════════════
char c = 'A'; // 单引号，基本类型，2 字节
String s = "A"; // 双引号，引用类型，对象
// 内存占用不同
char[] chars = {'H', 'e', 'l', 'l', 'o'}; // 10 字节
String str = "Hello"; // 对象头 + 引用 + char[] + ...（更多）
// 运算不同
System.out.println('A' + 'B'); // 131 (int 相加)
System.out.println("A" + "B"); // "AB" (字符串拼接)
System.out.println('A' + "B"); // "AB" (char 转 String 后拼接)
// 空值不同
char c1 = '\u0000'; // char 的"空"值
String s1 = null; // String 可以为 null
String s2 = ""; // String 可以为空串
4.3 常用转义字符
<mxfile>
<diagram id="escape-characters" name="常用转义字符">
<mxGraphModel dx="900" dy="700" grid="1" gridSize="10" guides="1" tooltips="1" connect="1" arrows="1" fold="1" page="1" pageScale="1" pageWidth="900" pageHeight="700" math="0" shadow="0">
<root>
<mxCell id="0" />
<mxCell id="1" parent="0" />
<!-- 主容器 -->
<mxCell id="2" value="" style="rounded=1;whiteSpace=wrap;html=1;fillColor=#fafafa;strokeColor=#5c6bc0;strokeWidth=3;shadow=1;" vertex="1" parent="1">
<mxGeometry x="80" y="30" width="740" height="620" as="geometry" />
</mxCell>
<!-- 标题 -->
<mxCell id="3" value="常用转义字符" style="text;html=1;strokeColor=none;fillColor=none;align=center;verticalAlign=middle;whiteSpace=wrap;rounded=0;fontSize=26;fontStyle=1;fontColor=#1a237e;" vertex="1" parent="1">
<mxGeometry x="250" y="50" width="400" height="50" as="geometry" />
</mxCell>
<!-- 表头背景 -->
<mxCell id="4" value="" style="rounded=1;whiteSpace=wrap;html=1;fillColor=#3949ab;strokeColor=none;arcSize=5;" vertex="1" parent="1">
<mxGeometry x="120" y="115" width="660" height="55" as="geometry" />
</mxCell>
<!-- 表头 - 转义字符 -->
<mxCell id="5" value="转义字符" style="text;html=1;strokeColor=none;fillColor=none;align=center;verticalAlign=middle;whiteSpace=wrap;rounded=0;fontSize=18;fontStyle=1;fontColor=#ffffff;" vertex="1" parent="1">
<mxGeometry x="120" y="115" width="180" height="55" as="geometry" />
</mxCell>
<!-- 表头 - 说明 -->
<mxCell id="6" value="说明" style="text;html=1;strokeColor=none;fillColor=none;align=center;verticalAlign=middle;whiteSpace=wrap;rounded=0;fontSize=18;fontStyle=1;fontColor=#ffffff;" vertex="1" parent="1">
<mxGeometry x="300" y="115" width="480" height="55" as="geometry" />
</mxCell>
<!-- 垂直分隔线 -->
<mxCell id="7" value="" style="endArrow=none;html=1;strokeColor=#e0e0e0;strokeWidth=2;" edge="1" parent="1">
<mxGeometry width="50" height="50" relative="1" as="geometry">
<mxPoint x="300" y="170" as="sourcePoint" />
<mxPoint x="300" y="610" as="targetPoint" />
</mxGeometry>
</mxCell>
<!-- 行1: \n -->
<mxCell id="8" value="" style="rounded=0;whiteSpace=wrap;html=1;fillColor=#e3f2fd;strokeColor=none;" vertex="1" parent="1">
<mxGeometry x="120" y="170" width="660" height="48" as="geometry" />
</mxCell>
<mxCell id="9" value="" style="rounded=1;whiteSpace=wrap;html=1;fillColor=#1565c0;strokeColor=none;" vertex="1" parent="1">
<mxGeometry x="145" y="179" width="110" height="30" as="geometry" />
</mxCell>
<mxCell id="10" value="<font face="Courier New"><b>\n</b></font>" style="text;html=1;strokeColor=none;fillColor=none;align=center;verticalAlign=middle;whiteSpace=wrap;rounded=0;fontSize=16;fontColor=#ffffff;" vertex="1" parent="1">
<mxGeometry x="145" y="179" width="110" height="30" as="geometry" />
</mxCell>
<mxCell id="11" value="换行符 (LF)" style="text;html=1;strokeColor=none;fillColor=none;align=left;verticalAlign=middle;whiteSpace=wrap;rounded=0;fontSize=15;" vertex="1" parent="1">
<mxGeometry x="320" y="170" width="440" height="48" as="geometry" />
</mxCell>
<!-- 行2: \r -->
<mxCell id="12" value="" style="rounded=0;whiteSpace=wrap;html=1;fillColor=#ffffff;strokeColor=none;" vertex="1" parent="1">
<mxGeometry x="120" y="218" width="660" height="48" as="geometry" />
</mxCell>
<mxCell id="13" value="" style="rounded=1;whiteSpace=wrap;html=1;fillColor=#2e7d32;strokeColor=none;" vertex="1" parent="1">
<mxGeometry x="145" y="227" width="110" height="30" as="geometry" />
</mxCell>
<mxCell id="14" value="<font face="Courier New"><b>\r</b></font>" style="text;html=1;strokeColor=none;fillColor=none;align=center;verticalAlign=middle;whiteSpace=wrap;rounded=0;fontSize=16;fontColor=#ffffff;" vertex="1" parent="1">
<mxGeometry x="145" y="227" width="110" height="30" as="geometry" />
</mxCell>
<mxCell id="15" value="回车符 (CR)" style="text;html=1;strokeColor=none;fillColor=none;align=left;verticalAlign=middle;whiteSpace=wrap;rounded=0;fontSize=15;" vertex="1" parent="1">
<mxGeometry x="320" y="218" width="440" height="48" as="geometry" />
</mxCell>
<!-- 行3: \t -->
<mxCell id="16" value="" style="rounded=0;whiteSpace=wrap;html=1;fillColor=#e3f2fd;strokeColor=none;" vertex="1" parent="1">
<mxGeometry x="120" y="266" width="660" height="48" as="geometry" />
</mxCell>
<mxCell id="17" value="" style="rounded=1;whiteSpace=wrap;html=1;fillColor=#6a1b9a;strokeColor=none;" vertex="1" parent="1">
<mxGeometry x="145" y="275" width="110" height="30" as="geometry" />
</mxCell>
<mxCell id="18" value="<font face="Courier New"><b>\t</b></font>" style="text;html=1;strokeColor=none;fillColor=none;align=center;verticalAlign=middle;whiteSpace=wrap;rounded=0;fontSize=16;fontColor=#ffffff;" vertex="1" parent="1">
<mxGeometry x="145" y="275" width="110" height="30" as="geometry" />
</mxCell>
<mxCell id="19" value="制表符 (Tab)" style="text;html=1;strokeColor=none;fillColor=none;align=left;verticalAlign=middle;whiteSpace=wrap;rounded=0;fontSize=15;" vertex="1" parent="1">
<mxGeometry x="320" y="266" width="440" height="48" as="geometry" />
</mxCell>
<!-- 行4: \\ -->
<mxCell id="20" value="" style="rounded=0;whiteSpace=wrap;html=1;fillColor=#ffffff;strokeColor=none;" vertex="1" parent="1">
<mxGeometry x="120" y="314" width="660" height="48" as="geometry" />
</mxCell>
<mxCell id="21" value="" style="rounded=1;whiteSpace=wrap;html=1;fillColor=#c62828;strokeColor=none;" vertex="1" parent="1">
<mxGeometry x="145" y="323" width="110" height="30" as="geometry" />
</mxCell>
<mxCell id="22" value="<font face="Courier New"><b>\\</b></font>" style="text;html=1;strokeColor=none;fillColor=none;align=center;verticalAlign=middle;whiteSpace=wrap;rounded=0;fontSize=16;fontColor=#ffffff;" vertex="1" parent="1">
<mxGeometry x="145" y="323" width="110" height="30" as="geometry" />
</mxCell>
<mxCell id="23" value="反斜杠" style="text;html=1;strokeColor=none;fillColor=none;align=left;verticalAlign=middle;whiteSpace=wrap;rounded=0;fontSize=15;" vertex="1" parent="1">
<mxGeometry x="320" y="314" width="440" height="48" as="geometry" />
</mxCell>
<!-- 行5: \' -->
<mxCell id="24" value="" style="rounded=0;whiteSpace=wrap;html=1;fillColor=#e3f2fd;strokeColor=none;" vertex="1" parent="1">
<mxGeometry x="120" y="362" width="660" height="48" as="geometry" />
</mxCell>
<mxCell id="25" value="" style="rounded=1;whiteSpace=wrap;html=1;fillColor=#ef6c00;strokeColor=none;" vertex="1" parent="1">
<mxGeometry x="145" y="371" width="110" height="30" as="geometry" />
</mxCell>
<mxCell id="26" value="<font face="Courier New"><b>\'</b></font>" style="text;html=1;strokeColor=none;fillColor=none;align=center;verticalAlign=middle;whiteSpace=wrap;rounded=0;fontSize=16;fontColor=#ffffff;" vertex="1" parent="1">
<mxGeometry x="145" y="371" width="110" height="30" as="geometry" />
</mxCell>
<mxCell id="27" value="单引号" style="text;html=1;strokeColor=none;fillColor=none;align=left;verticalAlign=middle;whiteSpace=wrap;rounded=0;fontSize=15;" vertex="1" parent="1">
<mxGeometry x="320" y="362" width="440" height="48" as="geometry" />
</mxCell>
<!-- 行6: \" -->
<mxCell id="28" value="" style="rounded=0;whiteSpace=wrap;html=1;fillColor=#ffffff;strokeColor=none;" vertex="1" parent="1">
<mxGeometry x="120" y="410" width="660" height="48" as="geometry" />
</mxCell>
<mxCell id="29" value="" style="rounded=1;whiteSpace=wrap;html=1;fillColor=#00838f;strokeColor=none;" vertex="1" parent="1">
<mxGeometry x="145" y="419" width="110" height="30" as="geometry" />
</mxCell>
<mxCell id="30" value="<font face="Courier New"><b>\"</b></font>" style="text;html=1;strokeColor=none;fillColor=none;align=center;verticalAlign=middle;whiteSpace=wrap;rounded=0;fontSize=16;fontColor=#ffffff;" vertex="1" parent="1">
<mxGeometry x="145" y="419" width="110" height="30" as="geometry" />
</mxCell>
<mxCell id="31" value="双引号" style="text;html=1;strokeColor=none;fillColor=none;align=left;verticalAlign=middle;whiteSpace=wrap;rounded=0;fontSize=15;" vertex="1" parent="1">
<mxGeometry x="320" y="410" width="440" height="48" as="geometry" />
</mxCell>
<!-- 行7: \b -->
<mxCell id="32" value="" style="rounded=0;whiteSpace=wrap;html=1;fillColor=#e3f2fd;strokeColor=none;" vertex="1" parent="1">
<mxGeometry x="120" y="458" width="660" height="48" as="geometry" />
</mxCell>
<mxCell id="33" value="" style="rounded=1;whiteSpace=wrap;html=1;fillColor=#5d4037;strokeColor=none;" vertex="1" parent="1">
<mxGeometry x="145" y="467" width="110" height="30" as="geometry" />
</mxCell>
<mxCell id="34" value="<font face="Courier New"><b>\b</b></font>" style="text;html=1;strokeColor=none;fillColor=none;align=center;verticalAlign=middle;whiteSpace=wrap;rounded=0;fontSize=16;fontColor=#ffffff;" vertex="1" parent="1">
<mxGeometry x="145" y="467" width="110" height="30" as="geometry" />
</mxCell>
<mxCell id="35" value="退格符" style="text;html=1;strokeColor=none;fillColor=none;align=left;verticalAlign=middle;whiteSpace=wrap;rounded=0;fontSize=15;" vertex="1" parent="1">
<mxGeometry x="320" y="458" width="440" height="48" as="geometry" />
</mxCell>
<!-- 行8: \f -->
<mxCell id="36" value="" style="rounded=0;whiteSpace=wrap;html=1;fillColor=#ffffff;strokeColor=none;" vertex="1" parent="1">
<mxGeometry x="120" y="506" width="660" height="48" as="geometry" />
</mxCell>
<mxCell id="37" value="" style="rounded=1;whiteSpace=wrap;html=1;fillColor=#455a64;strokeColor=none;" vertex="1" parent="1">
<mxGeometry x="145" y="515" width="110" height="30" as="geometry" />
</mxCell>
<mxCell id="38" value="<font face="Courier New"><b>\f</b></font>" style="text;html=1;strokeColor=none;fillColor=none;align=center;verticalAlign=middle;whiteSpace=wrap;rounded=0;fontSize=16;fontColor=#ffffff;" vertex="1" parent="1">
<mxGeometry x="145" y="515" width="110" height="30" as="geometry" />
</mxCell>
<mxCell id="39" value="换页符" style="text;html=1;strokeColor=none;fillColor=none;align=left;verticalAlign=middle;whiteSpace=wrap;rounded=0;fontSize=15;" vertex="1" parent="1">
<mxGeometry x="320" y="506" width="440" height="48" as="geometry" />
</mxCell>
<!-- 行9: \uXXXX -->
<mxCell id="40" value="" style="rounded=0;whiteSpace=wrap;html=1;fillColor=#fff3e0;strokeColor=none;" vertex="1" parent="1">
<mxGeometry x="120" y="554" width="660" height="56" as="geometry" />
</mxCell>
<mxCell id="41" value="" style="rounded=1;whiteSpace=wrap;html=1;fillColor=#d84315;strokeColor=none;" vertex="1" parent="1">
<mxGeometry x="145" y="567" width="110" height="30" as="geometry" />
</mxCell>
<mxCell id="42" value="<font face="Courier New"><b>\uXXXX</b></font>" style="text;html=1;strokeColor=none;fillColor=none;align=center;verticalAlign=middle;whiteSpace=wrap;rounded=0;fontSize=14;fontColor=#ffffff;" vertex="1" parent="1">
<mxGeometry x="145" y="567" width="110" height="30" as="geometry" />
</mxCell>
<mxCell id="43" value="Unicode 字符（4 位十六进制）" style="text;html=1;strokeColor=none;fillColor=none;align=left;verticalAlign=middle;whiteSpace=wrap;rounded=0;fontSize=15;" vertex="1" parent="1">
<mxGeometry x="320" y="554" width="350" height="56" as="geometry" />
</mxCell>
<!-- Unicode 示例标签 -->
<mxCell id="44" value="" style="rounded=1;whiteSpace=wrap;html=1;fillColor=#ffccbc;strokeColor=#ff7043;" vertex="1" parent="1">
<mxGeometry x="620" y="567" width="140" height="30" as="geometry" />
</mxCell>
<mxCell id="45" value="例: <font face="Courier New">\u0041</font> = A" style="text;html=1;strokeColor=none;fillColor=none;align=center;verticalAlign=middle;whiteSpace=wrap;rounded=0;fontSize=12;fontColor=#d84315;" vertex="1" parent="1">
<mxGeometry x="620" y="567" width="140" height="30" as="geometry" />
</mxCell>
</root>
</mxGraphModel>
</diagram>
</mxfile>
五、布尔类型
public class BooleanDemo {
public static void main(String[] args) {
// ═══════════════════════════════════════════════════════════════
// boolean 只有两个值
// ═══════════════════════════════════════════════════════════════
boolean flag = true;
boolean isEmpty = false;
// ═══════════════════════════════════════════════════════════════
// boolean 不能与其他类型转换
// ═══════════════════════════════════════════════════════════════
// int num = true; // ❌ 编译错误
// boolean b = 1; // ❌ 编译错误
// if (1) { } // ❌ 编译错误（不像 C/C++）
// 正确写法
int num = 1;
if (num != 0) { } // ✅ 显式比较
if (flag) { } // ✅ 直接使用 boolean
// ═══════════════════════════════════════════════════════════════
// boolean 的大小
// ═══════════════════════════════════════════════════════════════
// JVM 规范未明确定义 boolean 的大小
// 实际实现中：
// - 单个 boolean 通常占 4 字节（作为 int 处理）
// - boolean 数组中每个元素占 1 字节
}
}
<mxfile>
<diagram id="boolean-jvm" name="boolean的JVM实现">
<mxGraphModel dx="900" dy="700" grid="1" gridSize="10" guides="1" tooltips="1" connect="1" arrows="1" fold="1" page="1" pageScale="1" pageWidth="900" pageHeight="700">
<root>
<mxCell id="0" />
<mxCell id="1" parent="0" />
<mxCell id="2" value="boolean 的 JVM 实现" style="text;html=1;strokeColor=none;fillColor=none;align=center;verticalAlign=middle;fontSize=26;fontStyle=1;fontColor=#1E293B;" vertex="1" parent="1">
<mxGeometry x="250" y="20" width="400" height="40" as="geometry" />
</mxCell>
<mxCell id="3" value="深入理解 JVM 规范中的 boolean 处理机制" style="text;html=1;strokeColor=none;fillColor=#8B5CF6;align=center;verticalAlign=middle;fontSize=12;fontColor=#FFFFFF;rounded=1;" vertex="1" parent="1">
<mxGeometry x="275" y="58" width="350" height="25" as="geometry" />
</mxCell>
<mxCell id="4" value="⚠️ 核心事实" style="text;html=1;strokeColor=none;fillColor=#EF4444;align=center;verticalAlign=middle;fontSize=14;fontStyle=1;fontColor=#FFFFFF;rounded=1;" vertex="1" parent="1">
<mxGeometry x="40" y="100" width="110" height="30" as="geometry" />
</mxCell>
<mxCell id="5" value="" style="rounded=1;whiteSpace=wrap;html=1;fillColor=#FEF2F2;strokeColor=#EF4444;strokeWidth=2;" vertex="1" parent="1">
<mxGeometry x="40" y="140" width="820" height="50" as="geometry" />
</mxCell>
<mxCell id="6" value="JVM 规范中，boolean 没有专门的字节码指令！" style="text;html=1;strokeColor=none;fillColor=none;align=center;verticalAlign=middle;fontSize=16;fontStyle=1;fontColor=#991B1B;" vertex="1" parent="1">
<mxGeometry x="200" y="150" width="500" height="30" as="geometry" />
</mxCell>
<mxCell id="7" value="单个 boolean 变量" style="text;html=1;strokeColor=none;fillColor=#3B82F6;align=center;verticalAlign=middle;fontSize=14;fontStyle=1;fontColor=#FFFFFF;rounded=1;" vertex="1" parent="1">
<mxGeometry x="40" y="210" width="160" height="30" as="geometry" />
</mxCell>
<mxCell id="8" value="" style="rounded=1;whiteSpace=wrap;html=1;fillColor=#EFF6FF;strokeColor=#3B82F6;strokeWidth=2;" vertex="1" parent="1">
<mxGeometry x="40" y="250" width="400" height="170" as="geometry" />
</mxCell>
<mxCell id="9" value="使用 int 的指令处理" style="text;html=1;strokeColor=none;fillColor=#DBEAFE;align=center;verticalAlign=middle;fontSize=13;fontStyle=1;fontColor=#1E40AF;rounded=1;" vertex="1" parent="1">
<mxGeometry x="55" y="265" width="160" height="28" as="geometry" />
</mxCell>
<mxCell id="10" value="" style="rounded=1;whiteSpace=wrap;html=1;fillColor=#FFFFFF;strokeColor=#BFDBFE;strokeWidth=1;" vertex="1" parent="1">
<mxGeometry x="55" y="305" width="160" height="100" as="geometry" />
</mxCell>
<mxCell id="11" value="值映射" style="text;html=1;strokeColor=none;fillColor=#3B82F6;align=center;verticalAlign=middle;fontSize=11;fontStyle=1;fontColor=#FFFFFF;rounded=1;" vertex="1" parent="1">
<mxGeometry x="65" y="315" width="60" height="20" as="geometry" />
</mxCell>
<mxCell id="12" value="true" style="rounded=0;whiteSpace=wrap;html=1;fillColor=#22C55E;strokeColor=#16A34A;strokeWidth=1;fontSize=14;fontStyle=1;fontColor=#FFFFFF;fontFamily=Courier New;" vertex="1" parent="1">
<mxGeometry x="70" y="345" width="55" height="28" as="geometry" />
</mxCell>
<mxCell id="13" value="→" style="text;html=1;strokeColor=none;fillColor=none;align=center;verticalAlign=middle;fontSize=16;fontStyle=1;fontColor=#64748B;" vertex="1" parent="1">
<mxGeometry x="125" y="345" width="30" height="28" as="geometry" />
</mxCell>
<mxCell id="14" value="1" style="rounded=0;whiteSpace=wrap;html=1;fillColor=#1E293B;strokeColor=#0F172A;strokeWidth=1;fontSize=14;fontStyle=1;fontColor=#22C55E;fontFamily=Courier New;" vertex="1" parent="1">
<mxGeometry x="155" y="345" width="45" height="28" as="geometry" />
</mxCell>
<mxCell id="15" value="false" style="rounded=0;whiteSpace=wrap;html=1;fillColor=#EF4444;strokeColor=#DC2626;strokeWidth=1;fontSize=14;fontStyle=1;fontColor=#FFFFFF;fontFamily=Courier New;" vertex="1" parent="1">
<mxGeometry x="70" y="378" width="55" height="28" as="geometry" />
</mxCell>
<mxCell id="16" value="→" style="text;html=1;strokeColor=none;fillColor=none;align=center;verticalAlign=middle;fontSize=16;fontStyle=1;fontColor=#64748B;" vertex="1" parent="1">
<mxGeometry x="125" y="378" width="30" height="28" as="geometry" />
</mxCell>
<mxCell id="17" value="0" style="rounded=0;whiteSpace=wrap;html=1;fillColor=#1E293B;strokeColor=#0F172A;strokeWidth=1;fontSize=14;fontStyle=1;fontColor=#EF4444;fontFamily=Courier New;" vertex="1" parent="1">
<mxGeometry x="155" y="378" width="45" height="28" as="geometry" />
</mxCell>
<mxCell id="18" value="" style="rounded=1;whiteSpace=wrap;html=1;fillColor=#FFFFFF;strokeColor=#BFDBFE;strokeWidth=1;" vertex="1" parent="1">
<mxGeometry x="230" y="305" width="195" height="100" as="geometry" />
</mxCell>
<mxCell id="19" value="实际内存占用" style="text;html=1;strokeColor=none;fillColor=#F59E0B;align=center;verticalAlign=middle;fontSize=11;fontStyle=1;fontColor=#FFFFFF;rounded=1;" vertex="1" parent="1">
<mxGeometry x="240" y="315" width="90" height="20" as="geometry" />
</mxCell>
<mxCell id="20" value="4 字节" style="text;html=1;strokeColor=none;fillColor=#FEF3C7;align=center;verticalAlign=middle;fontSize=24;fontStyle=1;fontColor=#92400E;rounded=1;" vertex="1" parent="1">
<mxGeometry x="255" y="350" width="100" height="40" as="geometry" />
</mxCell>
<mxCell id="21" value="= 32 位" style="text;html=1;strokeColor=none;fillColor=none;align=center;verticalAlign=middle;fontSize=12;fontColor=#78350F;" vertex="1" parent="1">
<mxGeometry x="355" y="355" width="55" height="30" as="geometry" />
</mxCell>
<mxCell id="22" value="(与 int 相同)" style="text;html=1;strokeColor=none;fillColor=none;align=center;verticalAlign=middle;fontSize=10;fontColor=#92400E;" vertex="1" parent="1">
<mxGeometry x="265" y="390" width="80" height="18" as="geometry" />
</mxCell>
<mxCell id="23" value="boolean 数组" style="text;html=1;strokeColor=none;fillColor=#22C55E;align=center;verticalAlign=middle;fontSize=14;fontStyle=1;fontColor=#FFFFFF;rounded=1;" vertex="1" parent="1">
<mxGeometry x="460" y="210" width="120" height="30" as="geometry" />
</mxCell>
<mxCell id="24" value="" style="rounded=1;whiteSpace=wrap;html=1;fillColor=#F0FDF4;strokeColor=#22C55E;strokeWidth=2;" vertex="1" parent="1">
<mxGeometry x="460" y="250" width="400" height="170" as="geometry" />
</mxCell>
<mxCell id="25" value="使用 byte 数组实现" style="text;html=1;strokeColor=none;fillColor=#DCFCE7;align=center;verticalAlign=middle;fontSize=13;fontStyle=1;fontColor=#166534;rounded=1;" vertex="1" parent="1">
<mxGeometry x="475" y="265" width="150" height="28" as="geometry" />
</mxCell>
<mxCell id="26" value="" style="rounded=1;whiteSpace=wrap;html=1;fillColor=#FFFFFF;strokeColor=#BBF7D0;strokeWidth=1;" vertex="1" parent="1">
<mxGeometry x="475" y="305" width="370" height="100" as="geometry" />
</mxCell>
<mxCell id="27" value="每个元素占用" style="text;html=1;strokeColor=none;fillColor=#22C55E;align=center;verticalAlign=middle;fontSize=11;fontStyle=1;fontColor=#FFFFFF;rounded=1;" vertex="1" parent="1">
<mxGeometry x="485" y="315" width="90" height="20" as="geometry" />
</mxCell>
<mxCell id="28" value="1 字节" style="text;html=1;strokeColor=none;fillColor=#DCFCE7;align=center;verticalAlign=middle;fontSize=20;fontStyle=1;fontColor=#166534;rounded=1;" vertex="1" parent="1">
<mxGeometry x="495" y="345" width="80" height="35" as="geometry" />
</mxCell>
<mxCell id="29" value="= 8 位" style="text;html=1;strokeColor=none;fillColor=none;align=center;verticalAlign=middle;fontSize=11;fontColor=#166534;" vertex="1" parent="1">
<mxGeometry x="575" y="350" width="45" height="25" as="geometry" />
</mxCell>
<mxCell id="30" value="boolean[] 内存布局示意：" style="text;html=1;strokeColor=none;fillColor=none;align=left;verticalAlign=middle;fontSize=10;fontStyle=1;fontColor=#166534;spacingLeft=5;" vertex="1" parent="1">
<mxGeometry x="630" y="315" width="150" height="20" as="geometry" />
</mxCell>
<mxCell id="31" value="[0]" style="rounded=0;whiteSpace=wrap;html=1;fillColor=#22C55E;strokeColor=#16A34A;strokeWidth=1;fontSize=10;fontStyle=1;fontColor=#FFFFFF;" vertex="1" parent="1">
<mxGeometry x="640" y="340" width="35" height="30" as="geometry" />
</mxCell>
<mxCell id="32" value="[1]" style="rounded=0;whiteSpace=wrap;html=1;fillColor=#EF4444;strokeColor=#DC2626;strokeWidth=1;fontSize=10;fontStyle=1;fontColor=#FFFFFF;" vertex="1" parent="1">
<mxGeometry x="675" y="340" width="35" height="30" as="geometry" />
</mxCell>
<mxCell id="33" value="[2]" style="rounded=0;whiteSpace=wrap;html=1;fillColor=#22C55E;strokeColor=#16A34A;strokeWidth=1;fontSize=10;fontStyle=1;fontColor=#FFFFFF;" vertex="1" parent="1">
<mxGeometry x="710" y="340" width="35" height="30" as="geometry" />
</mxCell>
<mxCell id="34" value="[3]" style="rounded=0;whiteSpace=wrap;html=1;fillColor=#EF4444;strokeColor=#DC2626;strokeWidth=1;fontSize=10;fontStyle=1;fontColor=#FFFFFF;" vertex="1" parent="1">
<mxGeometry x="745" y="340" width="35" height="30" as="geometry" />
</mxCell>
<mxCell id="35" value="..." style="text;html=1;strokeColor=none;fillColor=none;align=center;verticalAlign=middle;fontSize=14;fontStyle=1;fontColor=#64748B;" vertex="1" parent="1">
<mxGeometry x="785" y="340" width="30" height="30" as="geometry" />
</mxCell>
<mxCell id="36" value="1B" style="text;html=1;strokeColor=none;fillColor=none;align=center;verticalAlign=middle;fontSize=9;fontColor=#64748B;" vertex="1" parent="1">
<mxGeometry x="640" y="370" width="35" height="15" as="geometry" />
</mxCell>
<mxCell id="37" value="1B" style="text;html=1;strokeColor=none;fillColor=none;align=center;verticalAlign=middle;fontSize=9;fontColor=#64748B;" vertex="1" parent="1">
<mxGeometry x="675" y="370" width="35" height="15" as="geometry" />
</mxCell>
<mxCell id="38" value="1B" style="text;html=1;strokeColor=none;fillColor=none;align=center;verticalAlign=middle;fontSize=9;fontColor=#64748B;" vertex="1" parent="1">
<mxGeometry x="710" y="370" width="35" height="15" as="geometry" />
</mxCell>
<mxCell id="39" value="1B" style="text;html=1;strokeColor=none;fillColor=none;align=center;verticalAlign=middle;fontSize=9;fontColor=#64748B;" vertex="1" parent="1">
<mxGeometry x="745" y="370" width="35" height="15" as="geometry" />
</mxCell>
<mxCell id="40" value="📝 字节码示例" style="text;html=1;strokeColor=none;fillColor=#8B5CF6;align=center;verticalAlign=middle;fontSize=14;fontStyle=1;fontColor=#FFFFFF;rounded=1;" vertex="1" parent="1">
<mxGeometry x="40" y="440" width="120" height="30" as="geometry" />
</mxCell>
<mxCell id="41" value="" style="rounded=1;whiteSpace=wrap;html=1;fillColor=#FAF5FF;strokeColor=#8B5CF6;strokeWidth=2;" vertex="1" parent="1">
<mxGeometry x="40" y="480" width="820" height="180" as="geometry" />
</mxCell>
<mxCell id="42" value="Java 源代码" style="text;html=1;strokeColor=none;fillColor=#8B5CF6;align=center;verticalAlign=middle;fontSize=12;fontStyle=1;fontColor=#FFFFFF;rounded=1;" vertex="1" parent="1">
<mxGeometry x="55" y="495" width="100" height="24" as="geometry" />
</mxCell>
<mxCell id="43" value="" style="rounded=1;whiteSpace=wrap;html=1;fillColor=#1E293B;strokeColor=#0F172A;strokeWidth=1;" vertex="1" parent="1">
<mxGeometry x="55" y="530" width="250" height="50" as="geometry" />
</mxCell>
<mxCell id="44" value="<font face="Courier New" color="#f472b6">boolean</font><font face="Courier New" color="#e2e8f0"> flag = </font><font face="Courier New" color="#4ade80">true</font><font face="Courier New" color="#e2e8f0">;</font>" style="text;html=1;strokeColor=none;fillColor=none;align=left;verticalAlign=middle;fontSize=14;spacingLeft=10;" vertex="1" parent="1">
<mxGeometry x="60" y="540" width="240" height="30" as="geometry" />
</mxCell>
<mxCell id="45" value="" style="shape=flexArrow;endArrow=classic;html=1;fillColor=#8B5CF6;strokeColor=none;width=20;endSize=6;endWidth=15;" edge="1" parent="1">
<mxGeometry width="50" height="50" relative="1" as="geometry">
<mxPoint x="320" y="555" as="sourcePoint" />
<mxPoint x="380" y="555" as="targetPoint" />
</mxGeometry>
</mxCell>
<mxCell id="46" value="编译" style="text;html=1;strokeColor=none;fillColor=none;align=center;verticalAlign=middle;fontSize=10;fontColor=#7C3AED;" vertex="1" parent="1">
<mxGeometry x="330" y="535" width="40" height="18" as="geometry" />
</mxCell>
<mxCell id="47" value="JVM 字节码" style="text;html=1;strokeColor=none;fillColor=#F59E0B;align=center;verticalAlign=middle;fontSize=12;fontStyle=1;fontColor=#FFFFFF;rounded=1;" vertex="1" parent="1">
<mxGeometry x="395" y="495" width="100" height="24" as="geometry" />
</mxCell>
<mxCell id="48" value="" style="rounded=1;whiteSpace=wrap;html=1;fillColor=#1E293B;strokeColor=#0F172A;strokeWidth=1;" vertex="1" parent="1">
<mxGeometry x="395" y="530" width="200" height="115" as="geometry" />
</mxCell>
<mxCell id="49" value="<font face="Courier New" color="#fbbf24">iconst_1</font>" style="text;html=1;strokeColor=none;fillColor=none;align=left;verticalAlign=middle;fontSize=14;spacingLeft=10;" vertex="1" parent="1">
<mxGeometry x="400" y="540" width="100" height="25" as="geometry" />
</mxCell>
<mxCell id="50" value="<font face="Courier New" color="#fbbf24">istore_1</font>" style="text;html=1;strokeColor=none;fillColor=none;align=left;verticalAlign=middle;fontSize=14;spacingLeft=10;" vertex="1" parent="1">
<mxGeometry x="400" y="570" width="100" height="25" as="geometry" />
</mxCell>
<mxCell id="51" value="<font color="#94a3b8">// 将常量 1 压栈</font>" style="text;html=1;strokeColor=none;fillColor=none;align=left;verticalAlign=middle;fontSize=11;fontFamily=Courier New;spacingLeft=5;" vertex="1" parent="1">
<mxGeometry x="400" y="600" width="180" height="20" as="geometry" />
</mxCell>
<mxCell id="52" value="<font color="#94a3b8">// 存储到局部变量表</font>" style="text;html=1;strokeColor=none;fillColor=none;align=left;verticalAlign=middle;fontSize=11;fontFamily=Courier New;spacingLeft=5;" vertex="1" parent="1">
<mxGeometry x="400" y="620" width="180" height="20" as="geometry" />
</mxCell>
<mxCell id="53" value="关键说明" style="text;html=1;strokeColor=none;fillColor=#EF4444;align=center;verticalAlign=middle;fontSize=12;fontStyle=1;fontColor=#FFFFFF;rounded=1;" vertex="1" parent="1">
<mxGeometry x="620" y="495" width="80" height="24" as="geometry" />
</mxCell>
<mxCell id="54" value="" style="rounded=1;whiteSpace=wrap;html=1;fillColor=#FEF2F2;strokeColor=#FECACA;strokeWidth=1;" vertex="1" parent="1">
<mxGeometry x="620" y="530" width="225" height="115" as="geometry" />
</mxCell>
<mxCell id="55" value="iconst_1" style="text;html=1;strokeColor=none;fillColor=#FEE2E2;align=center;verticalAlign=middle;fontSize=11;fontStyle=1;fontColor=#991B1B;fontFamily=Courier New;rounded=1;" vertex="1" parent="1">
<mxGeometry x="635" y="545" width="70" height="22" as="geometry" />
</mxCell>
<mxCell id="56" value="是 int 类型的指令" style="text;html=1;strokeColor=none;fillColor=none;align=left;verticalAlign=middle;fontSize=11;fontColor=#991B1B;spacingLeft=5;" vertex="1" parent="1">
<mxGeometry x="710" y="545" width="120" height="22" as="geometry" />
</mxCell>
<mxCell id="57" value="istore_1" style="text;html=1;strokeColor=none;fillColor=#FEE2E2;align=center;verticalAlign=middle;fontSize=11;fontStyle=1;fontColor=#991B1B;fontFamily=Courier New;rounded=1;" vertex="1" parent="1">
<mxGeometry x="635" y="575" width="70" height="22" as="geometry" />
</mxCell>
<mxCell id="58" value="是 int 类型的指令" style="text;html=1;strokeColor=none;fillColor=none;align=left;verticalAlign=middle;fontSize=11;fontColor=#991B1B;spacingLeft=5;" vertex="1" parent="1">
<mxGeometry x="710" y="575" width="120" height="22" as="geometry" />
</mxCell>
<mxCell id="59" value="💡 没有 bconst、bstore 指令！" style="text;html=1;strokeColor=none;fillColor=#F59E0B;align=center;verticalAlign=middle;fontSize=11;fontStyle=1;fontColor=#FFFFFF;rounded=1;" vertex="1" parent="1">
<mxGeometry x="635" y="610" width="195" height="25" as="geometry" />
</mxCell>
</root>
</mxGraphModel>
</diagram>
</mxfile>
六、类型转换
6.1 自动类型转换（隐式转换）
<mxfile>
<diagram id="auto-type-conversion" name="自动类型转换规则">
<mxGraphModel dx="900" dy="680" grid="1" gridSize="10" guides="1" tooltips="1" connect="1" arrows="1" fold="1" page="1" pageScale="1" pageWidth="900" pageHeight="680" math="0" shadow="0">
<root>
<mxCell id="0" />
<mxCell id="1" parent="0" />
<!-- 主容器 -->
<mxCell id="2" value="" style="rounded=1;whiteSpace=wrap;html=1;fillColor=#fafafa;strokeColor=#5c6bc0;strokeWidth=3;shadow=1;" vertex="1" parent="1">
<mxGeometry x="60" y="30" width="780" height="520" as="geometry" />
</mxCell>
<!-- 标题 -->
<mxCell id="3" value="自动类型转换规则" style="text;html=1;strokeColor=none;fillColor=none;align=center;verticalAlign=middle;whiteSpace=wrap;rounded=0;fontSize=26;fontStyle=1;fontColor=#1a237e;" vertex="1" parent="1">
<mxGeometry x="250" y="50" width="400" height="50" as="geometry" />
</mxCell>
<!-- 规则说明 -->
<mxCell id="4" value="" style="rounded=1;whiteSpace=wrap;html=1;fillColor=#e8f5e9;strokeColor=#4caf50;strokeWidth=2;" vertex="1" parent="1">
<mxGeometry x="100" y="115" width="700" height="50" as="geometry" />
</mxCell>
<mxCell id="5" value="小类型 → 大类型：自动转换，无精度损失" style="text;html=1;strokeColor=none;fillColor=none;align=center;verticalAlign=middle;whiteSpace=wrap;rounded=0;fontSize=18;fontColor=#2e7d32;fontStyle=1;" vertex="1" parent="1">
<mxGeometry x="100" y="115" width="700" height="50" as="geometry" />
</mxCell>
<!-- 转换流程图区域 -->
<mxCell id="6" value="" style="rounded=1;whiteSpace=wrap;html=1;fillColor=#e3f2fd;strokeColor=#1976d2;strokeWidth=2;dashed=1;" vertex="1" parent="1">
<mxGeometry x="100" y="185" width="700" height="200" as="geometry" />
</mxCell>
<!-- byte -->
<mxCell id="7" value="" style="rounded=1;whiteSpace=wrap;html=1;fillColor=#1565c0;strokeColor=none;shadow=1;" vertex="1" parent="1">
<mxGeometry x="120" y="230" width="80" height="45" as="geometry" />
</mxCell>
<mxCell id="8" value="<font face="Courier New"><b>byte</b></font>" style="text;html=1;strokeColor=none;fillColor=none;align=center;verticalAlign=middle;whiteSpace=wrap;rounded=0;fontSize=15;fontColor=#ffffff;" vertex="1" parent="1">
<mxGeometry x="120" y="230" width="80" height="45" as="geometry" />
</mxCell>
<!-- byte → short 箭头 -->
<mxCell id="9" value="" style="endArrow=classic;html=1;strokeColor=#1976d2;strokeWidth=3;entryX=0;entryY=0.5;exitX=1;exitY=0.5;" edge="1" parent="1">
<mxGeometry width="50" height="50" relative="1" as="geometry">
<mxPoint x="200" y="252" as="sourcePoint" />
<mxPoint x="230" y="252" as="targetPoint" />
</mxGeometry>
</mxCell>
<!-- short -->
<mxCell id="10" value="" style="rounded=1;whiteSpace=wrap;html=1;fillColor=#1976d2;strokeColor=none;shadow=1;" vertex="1" parent="1">
<mxGeometry x="230" y="230" width="80" height="45" as="geometry" />
</mxCell>
<mxCell id="11" value="<font face="Courier New"><b>short</b></font>" style="text;html=1;strokeColor=none;fillColor=none;align=center;verticalAlign=middle;whiteSpace=wrap;rounded=0;fontSize=15;fontColor=#ffffff;" vertex="1" parent="1">
<mxGeometry x="230" y="230" width="80" height="45" as="geometry" />
</mxCell>
<!-- short → int 箭头 -->
<mxCell id="12" value="" style="endArrow=classic;html=1;strokeColor=#1976d2;strokeWidth=3;" edge="1" parent="1">
<mxGeometry width="50" height="50" relative="1" as="geometry">
<mxPoint x="310" y="252" as="sourcePoint" />
<mxPoint x="340" y="252" as="targetPoint" />
</mxGeometry>
</mxCell>
<!-- int -->
<mxCell id="13" value="" style="rounded=1;whiteSpace=wrap;html=1;fillColor=#2196f3;strokeColor=none;shadow=1;" vertex="1" parent="1">
<mxGeometry x="340" y="230" width="80" height="45" as="geometry" />
</mxCell>
<mxCell id="14" value="<font face="Courier New"><b>int</b></font>" style="text;html=1;strokeColor=none;fillColor=none;align=center;verticalAlign=middle;whiteSpace=wrap;rounded=0;fontSize=15;fontColor=#ffffff;" vertex="1" parent="1">
<mxGeometry x="340" y="230" width="80" height="45" as="geometry" />
</mxCell>
<!-- int → long 箭头 -->
<mxCell id="15" value="" style="endArrow=classic;html=1;strokeColor=#1976d2;strokeWidth=3;" edge="1" parent="1">
<mxGeometry width="50" height="50" relative="1" as="geometry">
<mxPoint x="420" y="252" as="sourcePoint" />
<mxPoint x="450" y="252" as="targetPoint" />
</mxGeometry>
</mxCell>
<!-- long -->
<mxCell id="16" value="" style="rounded=1;whiteSpace=wrap;html=1;fillColor=#42a5f5;strokeColor=none;shadow=1;" vertex="1" parent="1">
<mxGeometry x="450" y="230" width="80" height="45" as="geometry" />
</mxCell>
<mxCell id="17" value="<font face="Courier New"><b>long</b></font>" style="text;html=1;strokeColor=none;fillColor=none;align=center;verticalAlign=middle;whiteSpace=wrap;rounded=0;fontSize=15;fontColor=#ffffff;" vertex="1" parent="1">
<mxGeometry x="450" y="230" width="80" height="45" as="geometry" />
</mxCell>
<!-- long → float 箭头 -->
<mxCell id="18" value="" style="endArrow=classic;html=1;strokeColor=#ff9800;strokeWidth=3;dashed=1;dashPattern=8 4;" edge="1" parent="1">
<mxGeometry width="50" height="50" relative="1" as="geometry">
<mxPoint x="530" y="252" as="sourcePoint" />
<mxPoint x="570" y="252" as="targetPoint" />
</mxGeometry>
</mxCell>
<!-- float -->
<mxCell id="19" value="" style="rounded=1;whiteSpace=wrap;html=1;fillColor=#7cb342;strokeColor=none;shadow=1;" vertex="1" parent="1">
<mxGeometry x="570" y="230" width="80" height="45" as="geometry" />
</mxCell>
<mxCell id="20" value="<font face="Courier New"><b>float</b></font>" style="text;html=1;strokeColor=none;fillColor=none;align=center;verticalAlign=middle;whiteSpace=wrap;rounded=0;fontSize=15;fontColor=#ffffff;" vertex="1" parent="1">
<mxGeometry x="570" y="230" width="80" height="45" as="geometry" />
</mxCell>
<!-- float → double 箭头 -->
<mxCell id="21" value="" style="endArrow=classic;html=1;strokeColor=#4caf50;strokeWidth=3;" edge="1" parent="1">
<mxGeometry width="50" height="50" relative="1" as="geometry">
<mxPoint x="650" y="252" as="sourcePoint" />
<mxPoint x="690" y="252" as="targetPoint" />
</mxGeometry>
</mxCell>
<!-- double -->
<mxCell id="22" value="" style="rounded=1;whiteSpace=wrap;html=1;fillColor=#2e7d32;strokeColor=none;shadow=1;" vertex="1" parent="1">
<mxGeometry x="690" y="230" width="90" height="45" as="geometry" />
</mxCell>
<mxCell id="23" value="<font face="Courier New"><b>double</b></font>" style="text;html=1;strokeColor=none;fillColor=none;align=center;verticalAlign=middle;whiteSpace=wrap;rounded=0;fontSize=15;fontColor=#ffffff;" vertex="1" parent="1">
<mxGeometry x="690" y="230" width="90" height="45" as="geometry" />
</mxCell>
<!-- char -->
<mxCell id="24" value="" style="rounded=1;whiteSpace=wrap;html=1;fillColor=#7b1fa2;strokeColor=none;shadow=1;" vertex="1" parent="1">
<mxGeometry x="120" y="320" width="80" height="45" as="geometry" />
</mxCell>
<mxCell id="25" value="<font face="Courier New"><b>char</b></font>" style="text;html=1;strokeColor=none;fillColor=none;align=center;verticalAlign=middle;whiteSpace=wrap;rounded=0;fontSize=15;fontColor=#ffffff;" vertex="1" parent="1">
<mxGeometry x="120" y="320" width="80" height="45" as="geometry" />
</mxCell>
<!-- char → int 箭头 (曲线) -->
<mxCell id="26" value="" style="endArrow=classic;html=1;strokeColor=#7b1fa2;strokeWidth=3;curved=0;exitX=1;exitY=0.5;entryX=0.5;entryY=1;" edge="1" parent="1">
<mxGeometry width="50" height="50" relative="1" as="geometry">
<mxPoint x="200" y="342" as="sourcePoint" />
<mxPoint x="380" y="275" as="targetPoint" /><Array as="points">
<mxPoint x="380" y="342" />
</Array>
</mxGeometry>
</mxCell>
<!-- char 到 byte 的向上箭头 -->
<mxCell id="27" value="" style="endArrow=none;html=1;strokeColor=#9e9e9e;strokeWidth=2;dashed=1;startArrow=classic;startFill=1;" edge="1" parent="1">
<mxGeometry width="50" height="50" relative="1" as="geometry">
<mxPoint x="160" y="320" as="sourcePoint" />
<mxPoint x="160" y="275" as="targetPoint" /></mxGeometry>
</mxCell>
<!-- 图例区域 -->
<mxCell id="28" value="" style="rounded=1;whiteSpace=wrap;html=1;fillColor=#fff8e1;strokeColor=#ffa000;strokeWidth=2;" vertex="1" parent="1">
<mxGeometry x="100" y="405" width="700" height="125" as="geometry" />
</mxCell>
<!-- 警告图标 -->
<mxCell id="29" value="⚠️" style="text;html=1;strokeColor=none;fillColor=none;align=center;verticalAlign=middle;whiteSpace=wrap;rounded=0;fontSize=28;" vertex="1" parent="1">
<mxGeometry x="115" y="415" width="50" height="50" as="geometry" />
</mxCell>
<!-- 注意标题 -->
<mxCell id="30" value="注意：精度损失风险" style="text;html=1;strokeColor=none;fillColor=none;align=left;verticalAlign=middle;whiteSpace=wrap;rounded=0;fontSize=16;fontStyle=1;fontColor=#e65100;" vertex="1" parent="1">
<mxGeometry x="165" y="420" width="200" height="35" as="geometry" />
</mxCell>
<!-- 图例 - 安全转换 -->
<mxCell id="31" value="" style="endArrow=classic;html=1;strokeColor=#1976d2;strokeWidth=3;" edge="1" parent="1">
<mxGeometry width="50" height="50" relative="1" as="geometry">
<mxPoint x="420" y="437" as="sourcePoint" />
<mxPoint x="480" y="437" as="targetPoint" />
</mxGeometry>
</mxCell>
<mxCell id="32" value="安全转换" style="text;html=1;strokeColor=none;fillColor=none;align=left;verticalAlign=middle;whiteSpace=wrap;rounded=0;fontSize=13;fontColor=#1976d2;" vertex="1" parent="1">
<mxGeometry x="490" y="422" width="80" height="30" as="geometry" />
</mxCell>
<!-- 图例 - 可能损失精度 -->
<mxCell id="33" value="" style="endArrow=classic;html=1;strokeColor=#ff9800;strokeWidth=3;dashed=1;dashPattern=8 4;" edge="1" parent="1">
<mxGeometry width="50" height="50" relative="1" as="geometry">
<mxPoint x="590" y="437" as="sourcePoint" />
<mxPoint x="650" y="437" as="targetPoint" />
</mxGeometry>
</mxCell>
<mxCell id="34" value="可能损失精度" style="text;html=1;strokeColor=none;fillColor=none;align=left;verticalAlign=middle;whiteSpace=wrap;rounded=0;fontSize=13;fontColor=#ff9800;" vertex="1" parent="1">
<mxGeometry x="660" y="422" width="120" height="30" as="geometry" />
</mxCell>
<!-- 详细说明1 -->
<mxCell id="35" value="" style="rounded=1;whiteSpace=wrap;html=1;fillColor=#ffccbc;strokeColor=#ff7043;" vertex="1" parent="1">
<mxGeometry x="130" y="460" width="300" height="55" as="geometry" />
</mxCell>
<mxCell id="36" value="<font face="Courier New" color="#d84315">int → float</font> 和 <font face="Courier New" color="#d84315">long → float/double</font><br>可能有精度损失" style="text;html=1;strokeColor=none;fillColor=none;align=center;verticalAlign=middle;whiteSpace=wrap;rounded=0;fontSize=13;" vertex="1" parent="1">
<mxGeometry x="130" y="460" width="300" height="55" as="geometry" />
</mxCell>
<!-- 详细说明2 -->
<mxCell id="37" value="" style="rounded=1;whiteSpace=wrap;html=1;fillColor=#e1bee7;strokeColor=#9c27b0;" vertex="1" parent="1">
<mxGeometry x="460" y="460" width="320" height="55" as="geometry" />
</mxCell>
<mxCell id="38" value="原因：浮点数的<b>尾数位有限</b><br><font face="Courier New">float</font> 尾数 23 位，<font face="Courier New">double</font> 尾数 52 位" style="text;html=1;strokeColor=none;fillColor=none;align=center;verticalAlign=middle;whiteSpace=wrap;rounded=0;fontSize=13;fontColor=#6a1b9a;" vertex="1" parent="1">
<mxGeometry x="460" y="460" width="320" height="55" as="geometry" />
</mxCell>
<!-- 类型大小标注 -->
<mxCell id="39" value="1字节" style="text;html=1;strokeColor=none;fillColor=none;align=center;verticalAlign=middle;whiteSpace=wrap;rounded=0;fontSize=10;fontColor=#757575;" vertex="1" parent="1">
<mxGeometry x="120" y="200" width="80" height="25" as="geometry" />
</mxCell>
<mxCell id="40" value="2字节" style="text;html=1;strokeColor=none;fillColor=none;align=center;verticalAlign=middle;whiteSpace=wrap;rounded=0;fontSize=10;fontColor=#757575;" vertex="1" parent="1">
<mxGeometry x="230" y="200" width="80" height="25" as="geometry" />
</mxCell>
<mxCell id="41" value="4字节" style="text;html=1;strokeColor=none;fillColor=none;align=center;verticalAlign=middle;whiteSpace=wrap;rounded=0;fontSize=10;fontColor=#757575;" vertex="1" parent="1">
<mxGeometry x="340" y="200" width="80" height="25" as="geometry" />
</mxCell>
<mxCell id="42" value="8字节" style="text;html=1;strokeColor=none;fillColor=none;align=center;verticalAlign=middle;whiteSpace=wrap;rounded=0;fontSize=10;fontColor=#757575;" vertex="1" parent="1">
<mxGeometry x="450" y="200" width="80" height="25" as="geometry" />
</mxCell>
<mxCell id="43" value="4字节" style="text;html=1;strokeColor=none;fillColor=none;align=center;verticalAlign=middle;whiteSpace=wrap;rounded=0;fontSize=10;fontColor=#757575;" vertex="1" parent="1">
<mxGeometry x="570" y="200" width="80" height="25" as="geometry" />
</mxCell>
<mxCell id="44" value="8字节" style="text;html=1;strokeColor=none;fillColor=none;align=center;verticalAlign=middle;whiteSpace=wrap;rounded=0;fontSize=10;fontColor=#757575;" vertex="1" parent="1">
<mxGeometry x="690" y="200" width="90" height="25" as="geometry" />
</mxCell>
<mxCell id="45" value="2字节" style="text;html=1;strokeColor=none;fillColor=none;align=center;verticalAlign=middle;whiteSpace=wrap;rounded=0;fontSize=10;fontColor=#757575;" vertex="1" parent="1">
<mxGeometry x="120" y="365" width="80" height="20" as="geometry" />
</mxCell>
</root>
</mxGraphModel>
</diagram>
</mxfile>
public class AutoConversionDemo {
public static void main(String[] args) {
// ═══════════════════════════════════════════════════════════════
// 自动类型转换
// ═══════════════════════════════════════════════════════════════
byte b = 10;
int i = b; // byte → int，自动转换
long l = i; // int → long，自动转换
float f = l; // long → float，自动转换
double d = f; // float → double，自动转换
char c = 'A';
int ic = c; // char → int，自动转换 (65)
// ═══════════════════════════════════════════════════════════════
// 精度损失示例
// ═══════════════════════════════════════════════════════════════
int bigInt = 123456789;
float floatVal = bigInt; // 自动转换，但有精度损失
System.out.println("int: " + bigInt); // 123456789
System.out.println("float: " + floatVal); // 1.23456792E8
System.out.println("转回int: " + (int)floatVal); // 123456792
long bigLong = 123456789012345678L;
double doubleVal = bigLong; // 精度损失
System.out.println("long: " + bigLong); // 123456789012345678
System.out.println("double: " + doubleVal); // 1.2345678901234568E17
}
}
6.2 强制类型转换（显式转换）
public class CastDemo {
public static void main(String[] args) {
// ═══════════════════════════════════════════════════════════════
// 大类型 → 小类型：需要强制转换
// ═══════════════════════════════════════════════════════════════
int i = 128;
byte b = (byte) i; // 必须强转
System.out.println("int 128 → byte = " + b); // -128 (溢出)
double d = 3.99;
int truncated = (int) d; // 截断小数部分
System.out.println("double 3.99 → int = " + truncated); // 3
// ═══════════════════════════════════════════════════════════════
// 强转可能导致数据丢失
// ═══════════════════════════════════════════════════════════════
int big = 300;
byte small = (byte) big;
System.out.println("int 300 → byte = " + small); // 44
// 原因分析：
// 300 的二进制: 00000000 00000000 00000001 00101100
// 截取低 8 位: 00101100 = 44
}
}
<mxfile>
<diagram id="type-cast-truncation" name="强制转换数据截断图解">
<mxGraphModel dx="1068" dy="484" grid="1" gridSize="10" guides="1" tooltips="1" connect="1" arrows="1" fold="1" page="1" pageScale="1" pageWidth="900" pageHeight="750" math="0" shadow="0">
<root>
<mxCell id="0" />
<mxCell id="1" parent="0" />
<mxCell id="2" parent="1" style="text;html=1;strokeColor=none;fillColor=none;align=center;verticalAlign=middle;fontSize=26;fontStyle=1;fontColor=#1E293B;" value="强制转换数据截断图解" vertex="1">
<mxGeometry height="40" width="450" x="225" y="15" as="geometry" />
</mxCell>
<mxCell id="3" parent="1" style="text;html=1;strokeColor=none;fillColor=#EF4444;align=center;verticalAlign=middle;fontSize=12;fontColor=#FFFFFF;rounded=1;" value="理解大类型转小类型时的数据丢失" vertex="1">
<mxGeometry height="25" width="300" x="300" y="52" as="geometry" />
</mxCell>
<mxCell id="4" parent="1" style="text;html=1;strokeColor=none;fillColor=#3B82F6;align=center;verticalAlign=middle;fontSize=14;fontStyle=1;fontColor=#FFFFFF;rounded=1;" value="示例 1：int 300 → byte" vertex="1">
<mxGeometry height="30" width="180" x="40" y="95" as="geometry" />
</mxCell>
<mxCell id="5" parent="1" style="rounded=1;whiteSpace=wrap;html=1;fillColor=#EFF6FF;strokeColor=#3B82F6;strokeWidth=2;" value="" vertex="1">
<mxGeometry height="250" width="820" x="40" y="135" as="geometry" />
</mxCell>
<mxCell id="6" parent="1" style="text;html=1;strokeColor=none;fillColor=#1E40AF;align=center;verticalAlign=middle;fontSize=13;fontStyle=1;fontColor=#FFFFFF;rounded=1;" value="int (32位)" vertex="1">
<mxGeometry height="26" width="90" x="60" y="155" as="geometry" />
</mxCell>
<mxCell id="7" parent="1" style="rounded=0;whiteSpace=wrap;html=1;fillColor=#E5E7EB;strokeColor=#9CA3AF;strokeWidth=2;fontSize=14;fontStyle=1;fontColor=#6B7280;fontFamily=Courier New;" value="00000000" vertex="1">
<mxGeometry height="36" width="100" x="170" y="150" as="geometry" />
</mxCell>
<mxCell id="8" parent="1" style="rounded=0;whiteSpace=wrap;html=1;fillColor=#E5E7EB;strokeColor=#9CA3AF;strokeWidth=2;fontSize=14;fontStyle=1;fontColor=#6B7280;fontFamily=Courier New;" value="00000000" vertex="1">
<mxGeometry height="36" width="100" x="270" y="150" as="geometry" />
</mxCell>
<mxCell id="9" parent="1" style="rounded=0;whiteSpace=wrap;html=1;fillColor=#FEE2E2;strokeColor=#EF4444;strokeWidth=2;fontSize=14;fontStyle=1;fontColor=#991B1B;fontFamily=Courier New;" value="00000001" vertex="1">
<mxGeometry height="36" width="100" x="370" y="150" as="geometry" />
</mxCell>
<mxCell id="10" parent="1" style="rounded=0;whiteSpace=wrap;html=1;fillColor=#DCFCE7;strokeColor=#22C55E;strokeWidth=2;fontSize=14;fontStyle=1;fontColor=#166534;fontFamily=Courier New;" value="00101100" vertex="1">
<mxGeometry height="36" width="100" x="470" y="150" as="geometry" />
</mxCell>
<mxCell id="11" parent="1" style="text;html=1;strokeColor=none;fillColor=#3B82F6;align=center;verticalAlign=middle;fontSize=16;fontStyle=1;fontColor=#FFFFFF;rounded=1;" value="= 300" vertex="1">
<mxGeometry height="32" width="70" x="590" y="152" as="geometry" />
</mxCell>
<mxCell id="12" parent="1" style="text;html=1;strokeColor=none;fillColor=#FEE2E2;align=center;verticalAlign=middle;fontSize=10;fontStyle=1;fontColor=#991B1B;rounded=1;" value="被截断" vertex="1">
<mxGeometry height="18" width="50" x="395" y="190" as="geometry" />
</mxCell>
<mxCell id="13" parent="1" style="text;html=1;strokeColor=none;fillColor=#DCFCE7;align=center;verticalAlign=middle;fontSize=10;fontStyle=1;fontColor=#166534;rounded=1;" value="保留" vertex="1">
<mxGeometry height="18" width="50" x="495" y="188" as="geometry" />
</mxCell>
<mxCell id="14" edge="1" parent="1" style="shape=flexArrow;endArrow=classic;html=1;fillColor=#EF4444;strokeColor=none;width=30;endSize=8;endWidth=25;" value="">
<mxGeometry height="50" relative="1" width="50" as="geometry">
<mxPoint x="520" y="220" as="sourcePoint" />
<mxPoint x="520" y="270" as="targetPoint" />
</mxGeometry>
</mxCell>
<mxCell id="15" parent="1" style="text;html=1;strokeColor=none;fillColor=none;align=center;verticalAlign=middle;fontSize=11;fontStyle=1;fontColor=#EF4444;" value="强制转换" vertex="1">
<mxGeometry height="20" width="70" x="540" y="235" as="geometry" />
</mxCell>
<mxCell id="16" parent="1" style="text;html=1;strokeColor=none;fillColor=#166534;align=center;verticalAlign=middle;fontSize=13;fontStyle=1;fontColor=#FFFFFF;rounded=1;" value="byte (8位)" vertex="1">
<mxGeometry height="26" width="90" x="60" y="285" as="geometry" />
</mxCell>
<mxCell id="17" parent="1" style="rounded=0;whiteSpace=wrap;html=1;fillColor=#22C55E;strokeColor=#16A34A;strokeWidth=3;fontSize=16;fontStyle=1;fontColor=#FFFFFF;fontFamily=Courier New;" value="00101100" vertex="1">
<mxGeometry height="40" width="100" x="470" y="280" as="geometry" />
</mxCell>
<mxCell id="18" parent="1" style="text;html=1;strokeColor=none;fillColor=#22C55E;align=center;verticalAlign=middle;fontSize=18;fontStyle=1;fontColor=#FFFFFF;rounded=1;" value="= 44" vertex="1">
<mxGeometry height="32" width="60" x="590" y="284" as="geometry" />
</mxCell>
<mxCell id="19" parent="1" style="text;html=1;strokeColor=none;fillColor=#FEF3C7;align=center;verticalAlign=middle;fontSize=12;fontStyle=1;fontColor=#92400E;rounded=1;" value="⚠️ 高位被截断，数值从 300 变成 44" vertex="1">
<mxGeometry height="28" width="280" x="380" y="335" as="geometry" />
</mxCell>
<mxCell id="20" parent="1" style="rounded=1;whiteSpace=wrap;html=1;fillColor=#FFFFFF;strokeColor=#BFDBFE;strokeWidth=1;" value="" vertex="1">
<mxGeometry height="130" width="165" x="680" y="150" as="geometry" />
</mxCell>
<mxCell id="21" parent="1" style="text;html=1;strokeColor=none;fillColor=#3B82F6;align=center;verticalAlign=middle;fontSize=11;fontStyle=1;fontColor=#FFFFFF;rounded=1;" value="💡 计算过程" vertex="1">
<mxGeometry height="22" width="85" x="690" y="160" as="geometry" />
</mxCell>
<mxCell id="22" parent="1" style="text;html=1;strokeColor=none;fillColor=none;align=left;verticalAlign=middle;fontSize=11;fontFamily=Courier New;fontColor=#1E40AF;spacingLeft=5;" value="300 = 256 + 44" vertex="1">
<mxGeometry height="20" width="140" x="690" y="190" as="geometry" />
</mxCell>
<mxCell id="23" parent="1" style="text;html=1;strokeColor=none;fillColor=none;align=left;verticalAlign=middle;fontSize=11;fontFamily=Courier New;fontColor=#1E40AF;spacingLeft=5;" value="300 % 256 = 44" vertex="1">
<mxGeometry height="20" width="140" x="690" y="215" as="geometry" />
</mxCell>
<mxCell id="24" parent="1" style="text;html=1;strokeColor=none;fillColor=#DBEAFE;align=center;verticalAlign=middle;fontSize=10;fontColor=#1E40AF;rounded=1;" value="byte范围: -128~127" vertex="1">
<mxGeometry height="20" width="120" x="695" y="245" as="geometry" />
</mxCell>
<mxCell id="25" parent="1" style="text;html=1;strokeColor=none;fillColor=#8B5CF6;align=center;verticalAlign=middle;fontSize=14;fontStyle=1;fontColor=#FFFFFF;rounded=1;" value="示例 2：int 128 → byte（符号位变化）" vertex="1">
<mxGeometry height="30" width="280" x="40" y="400" as="geometry" />
</mxCell>
<mxCell id="26" parent="1" style="rounded=1;whiteSpace=wrap;html=1;fillColor=#FAF5FF;strokeColor=#8B5CF6;strokeWidth=2;" value="" vertex="1">
<mxGeometry height="280" width="820" x="40" y="440" as="geometry" />
</mxCell>
<mxCell id="27" parent="1" style="text;html=1;strokeColor=none;fillColor=#6D28D9;align=center;verticalAlign=middle;fontSize=13;fontStyle=1;fontColor=#FFFFFF;rounded=1;" value="int (32位)" vertex="1">
<mxGeometry height="26" width="90" x="60" y="460" as="geometry" />
</mxCell>
<mxCell id="28" parent="1" style="rounded=0;whiteSpace=wrap;html=1;fillColor=#E5E7EB;strokeColor=#9CA3AF;strokeWidth=2;fontSize=14;fontStyle=1;fontColor=#6B7280;fontFamily=Courier New;" value="00000000" vertex="1">
<mxGeometry height="36" width="100" x="170" y="455" as="geometry" />
</mxCell>
<mxCell id="29" parent="1" style="rounded=0;whiteSpace=wrap;html=1;fillColor=#E5E7EB;strokeColor=#9CA3AF;strokeWidth=2;fontSize=14;fontStyle=1;fontColor=#6B7280;fontFamily=Courier New;" value="00000000" vertex="1">
<mxGeometry height="36" width="100" x="270" y="455" as="geometry" />
</mxCell>
<mxCell id="30" parent="1" style="rounded=0;whiteSpace=wrap;html=1;fillColor=#E5E7EB;strokeColor=#9CA3AF;strokeWidth=2;fontSize=14;fontStyle=1;fontColor=#6B7280;fontFamily=Courier New;" value="00000000" vertex="1">
<mxGeometry height="36" width="100" x="370" y="455" as="geometry" />
</mxCell>
<mxCell id="31" parent="1" style="rounded=0;whiteSpace=wrap;html=1;fillColor=#F3E8FF;strokeColor=#8B5CF6;strokeWidth=2;fontSize=14;fontStyle=1;fontColor=#6D28D9;fontFamily=Courier New;" value="10000000" vertex="1">
<mxGeometry height="36" width="100" x="470" y="455" as="geometry" />
</mxCell>
<mxCell id="32" parent="1" style="text;html=1;strokeColor=none;fillColor=#8B5CF6;align=center;verticalAlign=middle;fontSize=16;fontStyle=1;fontColor=#FFFFFF;rounded=1;" value="= 128" vertex="1">
<mxGeometry height="32" width="70" x="590" y="457" as="geometry" />
</mxCell>
<mxCell id="33" parent="1" style="text;html=1;strokeColor=none;fillColor=#22C55E;align=center;verticalAlign=middle;fontSize=10;fontStyle=1;fontColor=#FFFFFF;rounded=1;" value="正数" vertex="1">
<mxGeometry height="22" width="40" x="662.5" y="464" as="geometry" />
</mxCell>
<mxCell id="34" edge="1" parent="1" style="shape=flexArrow;endArrow=classic;html=1;fillColor=#8B5CF6;strokeColor=none;width=30;endSize=8;endWidth=25;" value="">
<mxGeometry height="50" relative="1" width="50" as="geometry">
<mxPoint x="520" y="510" as="sourcePoint" />
<mxPoint x="520" y="560" as="targetPoint" />
</mxGeometry>
</mxCell>
<mxCell id="35" parent="1" style="text;html=1;strokeColor=none;fillColor=none;align=center;verticalAlign=middle;fontSize=11;fontStyle=1;fontColor=#8B5CF6;" value="强制转换" vertex="1">
<mxGeometry height="20" width="70" x="540" y="525" as="geometry" />
</mxCell>
<mxCell id="36" parent="1" style="text;html=1;strokeColor=none;fillColor=#DC2626;align=center;verticalAlign=middle;fontSize=13;fontStyle=1;fontColor=#FFFFFF;rounded=1;" value="byte (8位)" vertex="1">
<mxGeometry height="26" width="90" x="60" y="575" as="geometry" />
</mxCell>
<mxCell id="37" parent="1" style="rounded=0;whiteSpace=wrap;html=1;fillColor=#EF4444;strokeColor=#DC2626;strokeWidth=3;fontSize=16;fontStyle=1;fontColor=#FFFFFF;fontFamily=Courier New;" value="" vertex="1">
<mxGeometry height="40" width="100" x="470" y="570" as="geometry" />
</mxCell>
<mxCell id="38" parent="1" style="rounded=0;whiteSpace=wrap;html=1;fillColor=#FEE2E2;strokeColor=#EF4444;strokeWidth=2;fontSize=16;fontStyle=1;fontColor=#DC2626;fontFamily=Courier New;" value="1" vertex="1">
<mxGeometry height="40" width="16" x="470" y="570" as="geometry" />
</mxCell>
<mxCell id="39" parent="1" style="text;html=1;strokeColor=none;fillColor=none;align=center;verticalAlign=middle;fontSize=16;fontStyle=1;fontColor=#FFFFFF;fontFamily=Courier New;" value="0000000" vertex="1">
<mxGeometry height="24" width="84" x="486" y="578" as="geometry" />
</mxCell>
<mxCell id="40" parent="1" style="text;html=1;strokeColor=none;fillColor=#EF4444;align=center;verticalAlign=middle;fontSize=18;fontStyle=1;fontColor=#FFFFFF;rounded=1;" value="= -128" vertex="1">
<mxGeometry height="32" width="70" x="590" y="574" as="geometry" />
</mxCell>
<mxCell id="41" parent="1" style="text;html=1;strokeColor=none;fillColor=#EF4444;align=center;verticalAlign=middle;fontSize=10;fontStyle=1;fontColor=#FFFFFF;rounded=1;" value="负数!" vertex="1">
<mxGeometry height="22" width="45" x="662.5" y="581" as="geometry" />
</mxCell>
<mxCell id="42" parent="1" style="text;html=1;strokeColor=none;fillColor=#EF4444;align=center;verticalAlign=middle;fontSize=9;fontStyle=1;fontColor=#FFFFFF;rounded=1;" value="符号位" vertex="1">
<mxGeometry height="16" width="45" x="455.5" y="619" as="geometry" />
</mxCell>
<mxCell id="43" edge="1" parent="1" style="endArrow=classic;html=1;strokeColor=#EF4444;strokeWidth=2;" value="">
<mxGeometry height="50" relative="1" width="50" as="geometry">
<mxPoint x="477.76" y="622" as="sourcePoint" />
<mxPoint x="477.76" y="606" as="targetPoint" />
</mxGeometry>
</mxCell>
<mxCell id="44" parent="1" style="rounded=1;whiteSpace=wrap;html=1;fillColor=#FFFFFF;strokeColor=#E9D5FF;strokeWidth=1;" value="" vertex="1">
<mxGeometry height="134" width="140" x="710" y="490" as="geometry" />
</mxCell>
<mxCell id="45" parent="1" style="text;html=1;strokeColor=none;fillColor=#8B5CF6;align=center;verticalAlign=middle;fontSize=11;fontStyle=1;fontColor=#FFFFFF;rounded=1;" value="⚡ 关键变化" vertex="1">
<mxGeometry height="22" width="85" x="720" y="496" as="geometry" />
</mxCell>
<mxCell id="46" parent="1" style="text;html=1;strokeColor=none;fillColor=none;align=left;verticalAlign=middle;fontSize=10;fontColor=#6D28D9;spacingLeft=5;" value="int 中: 最高位是数据位" vertex="1">
<mxGeometry height="18" width="145" x="720" y="526" as="geometry" />
</mxCell>
<mxCell id="47" parent="1" style="text;html=1;strokeColor=none;fillColor=none;align=left;verticalAlign=middle;fontSize=10;fontColor=#DC2626;spacingLeft=5;" value="byte中: 最高位是符号位" vertex="1">
<mxGeometry height="18" width="145" x="720" y="546" as="geometry" />
</mxCell>
<mxCell id="48" parent="1" style="text;html=1;strokeColor=none;fillColor=#FEE2E2;align=center;verticalAlign=middle;fontSize=10;fontStyle=1;fontColor=#991B1B;rounded=1;" value="1 → 表示负数" vertex="1">
<mxGeometry height="20" width="90" x="730" y="571" as="geometry" />
</mxCell>
<mxCell id="49" parent="1" style="text;html=1;strokeColor=none;fillColor=#EF4444;align=center;verticalAlign=middle;fontSize=11;fontStyle=1;fontColor=#FFFFFF;rounded=1;" value="128 变成 -128" vertex="1">
<mxGeometry height="22" width="100" x="725" y="596" as="geometry" />
</mxCell>
<mxCell id="50" parent="1" style="text;html=1;strokeColor=none;fillColor=#FEE2E2;align=center;verticalAlign=middle;fontSize=12;fontStyle=1;fontColor=#991B1B;rounded=1;" value="⚠️ 最高位从数据位变成符号位，正数变负数！" vertex="1">
<mxGeometry height="28" width="340" x="330" y="635" as="geometry" />
</mxCell>
<mxCell id="51" parent="1" style="text;html=1;strokeColor=none;fillColor=#1E293B;align=center;verticalAlign=middle;fontSize=13;fontStyle=1;fontColor=#FFFFFF;rounded=1;" value="📌 总结：强制转换可能导致数据截断和符号变化，使用时需谨慎！" vertex="1">
<mxGeometry height="35" width="550" x="175" y="680" as="geometry" />
</mxCell>
</root>
</mxGraphModel>
</diagram>
</mxfile>
6.3 表达式中的类型提升
public class TypePromotionDemo {
public static void main(String[] args) {
// ═══════════════════════════════════════════════════════════════
// 规则 1：byte、short、char 运算时自动提升为 int
// ═══════════════════════════════════════════════════════════════
byte b1 = 10;
byte b2 = 20;
// byte b3 = b1 + b2; // ❌ 编译错误，结果是 int
int i = b1 + b2; // ✅ 正确
byte b3 = (byte)(b1 + b2); // ✅ 强转
char c1 = 'A';
char c2 = 'B';
// char c3 = c1 + c2; // ❌ 编译错误
int ic = c1 + c2; // ✅ 正确，结果是 131
// ═══════════════════════════════════════════════════════════════
// 规则 2：表达式结果类型是最大的操作数类型
// ═══════════════════════════════════════════════════════════════
int a = 10;
long b = 20L;
float c = 1.5f;
double d = 2.5;
// int + long = long
long r1 = a + b;
// long + float = float
float r2 = b + c;
// float + double = double
double r3 = c + d;
// 混合运算：结果是 double
double r4 = a + b + c + d;
// ═══════════════════════════════════════════════════════════════
// 特殊情况：字面量
// ═══════════════════════════════════════════════════════════════
byte b4 = 10 + 20; // ✅ 编译期常量折叠，可以直接赋值
// byte b5 = b1 + 20; // ❌ 变量参与运算，结果是 int
final byte fb1 = 10;
final byte fb2 = 20;
byte b6 = fb1 + fb2; // ✅ final 常量，编译期可确定
}
}
七、包装类
7.1 基本类型与包装类对应关系
<mxfile>
<diagram id="primitive-wrapper-types-fixed" name="基本类型与包装类对应关系">
<mxGraphModel dx="1281" dy="654" grid="1" gridSize="10" guides="1" tooltips="1" connect="1" arrows="1" fold="1" page="1" pageScale="1" pageWidth="900" pageHeight="900" math="0" shadow="0">
<root>
<mxCell id="0" />
<mxCell id="1" parent="0" />
<mxCell id="2" parent="1" style="text;html=1;strokeColor=none;fillColor=none;align=center;verticalAlign=middle;fontSize=26;fontStyle=1;fontColor=#1E293B;" value="Java 基本类型与包装类对应关系" vertex="1">
<mxGeometry height="40" width="450" x="225" y="15" as="geometry" />
</mxCell>
<mxCell id="3" parent="1" style="text;html=1;strokeColor=none;fillColor=#3B82F6;align=center;verticalAlign=middle;fontSize=12;fontColor=#FFFFFF;rounded=1;" value="Java 8种基本类型及其包装类的映射与继承体系" vertex="1">
<mxGeometry height="25" width="400" x="250" y="52" as="geometry" />
</mxCell>
<mxCell id="4" parent="1" style="text;html=1;strokeColor=none;fillColor=#8B5CF6;align=center;verticalAlign=middle;fontSize=14;fontStyle=1;fontColor=#FFFFFF;rounded=1;" value="📋 对应关系表" vertex="1">
<mxGeometry height="28" width="120" x="40" y="95" as="geometry" />
</mxCell>
<mxCell id="5" parent="1" style="rounded=1;whiteSpace=wrap;html=1;fillColor=#F8FAFC;strokeColor=#E2E8F0;strokeWidth=2;" value="" vertex="1">
<mxGeometry height="307" width="820" x="40" y="133" as="geometry" />
</mxCell>
<mxCell id="6" parent="1" style="rounded=0;whiteSpace=wrap;html=1;fillColor=#1E293B;strokeColor=#0F172A;strokeWidth=1;fontSize=13;fontStyle=1;fontColor=#FFFFFF;" value="基本类型" vertex="1">
<mxGeometry height="35" width="120" x="60" y="150" as="geometry" />
</mxCell>
<mxCell id="7" parent="1" style="rounded=0;whiteSpace=wrap;html=1;fillColor=#1E293B;strokeColor=#0F172A;strokeWidth=1;fontSize=13;fontStyle=1;fontColor=#FFFFFF;" value="包装类" vertex="1">
<mxGeometry height="35" width="140" x="180" y="150" as="geometry" />
</mxCell>
<mxCell id="8" parent="1" style="rounded=0;whiteSpace=wrap;html=1;fillColor=#1E293B;strokeColor=#0F172A;strokeWidth=1;fontSize=13;fontStyle=1;fontColor=#FFFFFF;" value="继承关系" vertex="1">
<mxGeometry height="35" width="200" x="320" y="150" as="geometry" />
</mxCell>
<mxCell id="9" parent="1" style="rounded=0;whiteSpace=wrap;html=1;fillColor=#1E293B;strokeColor=#0F172A;strokeWidth=1;fontSize=13;fontStyle=1;fontColor=#FFFFFF;" value="分类" vertex="1">
<mxGeometry height="35" width="120" x="520" y="150" as="geometry" />
</mxCell>
<mxCell id="10" parent="1" style="rounded=0;whiteSpace=wrap;html=1;fillColor=#DBEAFE;strokeColor=#BFDBFE;strokeWidth=1;fontSize=12;fontStyle=1;fontColor=#1E40AF;fontFamily=Courier New;" value="byte" vertex="1">
<mxGeometry height="30" width="120" x="60" y="185" as="geometry" />
</mxCell>
<mxCell id="11" parent="1" style="rounded=0;whiteSpace=wrap;html=1;fillColor=#EFF6FF;strokeColor=#BFDBFE;strokeWidth=1;fontSize=12;fontStyle=1;fontColor=#1E40AF;fontFamily=Courier New;" value="Byte" vertex="1">
<mxGeometry height="30" width="140" x="180" y="185" as="geometry" />
</mxCell>
<mxCell id="12" parent="1" style="rounded=0;whiteSpace=wrap;html=1;fillColor=#EFF6FF;strokeColor=#BFDBFE;strokeWidth=1;fontSize=11;fontColor=#1E40AF;" value="Number → Object" vertex="1">
<mxGeometry height="30" width="200" x="320" y="185" as="geometry" />
</mxCell>
<mxCell id="13" parent="1" style="rounded=0;whiteSpace=wrap;html=1;fillColor=#3B82F6;strokeColor=#2563EB;strokeWidth=1;fontSize=11;fontStyle=1;fontColor=#FFFFFF;" value="数值型" vertex="1">
<mxGeometry height="30" width="120" x="520" y="185" as="geometry" />
</mxCell>
<mxCell id="14" parent="1" style="rounded=0;whiteSpace=wrap;html=1;fillColor=#DBEAFE;strokeColor=#BFDBFE;strokeWidth=1;fontSize=12;fontStyle=1;fontColor=#1E40AF;fontFamily=Courier New;" value="short" vertex="1">
<mxGeometry height="30" width="120" x="60" y="215" as="geometry" />
</mxCell>
<mxCell id="15" parent="1" style="rounded=0;whiteSpace=wrap;html=1;fillColor=#EFF6FF;strokeColor=#BFDBFE;strokeWidth=1;fontSize=12;fontStyle=1;fontColor=#1E40AF;fontFamily=Courier New;" value="Short" vertex="1">
<mxGeometry height="30" width="140" x="180" y="215" as="geometry" />
</mxCell>
<mxCell id="16" parent="1" style="rounded=0;whiteSpace=wrap;html=1;fillColor=#EFF6FF;strokeColor=#BFDBFE;strokeWidth=1;fontSize=11;fontColor=#1E40AF;" value="Number → Object" vertex="1">
<mxGeometry height="30" width="200" x="320" y="215" as="geometry" />
</mxCell>
<mxCell id="17" parent="1" style="rounded=0;whiteSpace=wrap;html=1;fillColor=#3B82F6;strokeColor=#2563EB;strokeWidth=1;fontSize=11;fontStyle=1;fontColor=#FFFFFF;" value="数值型" vertex="1">
<mxGeometry height="30" width="120" x="520" y="215" as="geometry" />
</mxCell>
<mxCell id="18" parent="1" style="rounded=0;whiteSpace=wrap;html=1;fillColor=#DBEAFE;strokeColor=#BFDBFE;strokeWidth=1;fontSize=12;fontStyle=1;fontColor=#1E40AF;fontFamily=Courier New;" value="int" vertex="1">
<mxGeometry height="30" width="120" x="60" y="245" as="geometry" />
</mxCell>
<mxCell id="19" parent="1" style="rounded=0;whiteSpace=wrap;html=1;fillColor=#EFF6FF;strokeColor=#BFDBFE;strokeWidth=1;fontSize=12;fontStyle=1;fontColor=#1E40AF;fontFamily=Courier New;" value="Integer" vertex="1">
<mxGeometry height="30" width="140" x="180" y="245" as="geometry" />
</mxCell>
<mxCell id="20" parent="1" style="rounded=0;whiteSpace=wrap;html=1;fillColor=#EFF6FF;strokeColor=#BFDBFE;strokeWidth=1;fontSize=11;fontColor=#1E40AF;" value="Number → Object" vertex="1">
<mxGeometry height="30" width="200" x="320" y="245" as="geometry" />
</mxCell>
<mxCell id="21" parent="1" style="rounded=0;whiteSpace=wrap;html=1;fillColor=#3B82F6;strokeColor=#2563EB;strokeWidth=1;fontSize=11;fontStyle=1;fontColor=#FFFFFF;" value="数值型" vertex="1">
<mxGeometry height="30" width="120" x="520" y="245" as="geometry" />
</mxCell>
<mxCell id="22" parent="1" style="rounded=0;whiteSpace=wrap;html=1;fillColor=#DBEAFE;strokeColor=#BFDBFE;strokeWidth=1;fontSize=12;fontStyle=1;fontColor=#1E40AF;fontFamily=Courier New;" value="long" vertex="1">
<mxGeometry height="30" width="120" x="60" y="275" as="geometry" />
</mxCell>
<mxCell id="23" parent="1" style="rounded=0;whiteSpace=wrap;html=1;fillColor=#EFF6FF;strokeColor=#BFDBFE;strokeWidth=1;fontSize=12;fontStyle=1;fontColor=#1E40AF;fontFamily=Courier New;" value="Long" vertex="1">
<mxGeometry height="30" width="140" x="180" y="275" as="geometry" />
</mxCell>
<mxCell id="24" parent="1" style="rounded=0;whiteSpace=wrap;html=1;fillColor=#EFF6FF;strokeColor=#BFDBFE;strokeWidth=1;fontSize=11;fontColor=#1E40AF;" value="Number → Object" vertex="1">
<mxGeometry height="30" width="200" x="320" y="275" as="geometry" />
</mxCell>
<mxCell id="25" parent="1" style="rounded=0;whiteSpace=wrap;html=1;fillColor=#3B82F6;strokeColor=#2563EB;strokeWidth=1;fontSize=11;fontStyle=1;fontColor=#FFFFFF;" value="数值型" vertex="1">
<mxGeometry height="30" width="120" x="520" y="275" as="geometry" />
</mxCell>
<mxCell id="26" parent="1" style="rounded=0;whiteSpace=wrap;html=1;fillColor=#FEF3C7;strokeColor=#FDE68A;strokeWidth=1;fontSize=12;fontStyle=1;fontColor=#92400E;fontFamily=Courier New;" value="float" vertex="1">
<mxGeometry height="30" width="120" x="60" y="305" as="geometry" />
</mxCell>
<mxCell id="27" parent="1" style="rounded=0;whiteSpace=wrap;html=1;fillColor=#FFFBEB;strokeColor=#FDE68A;strokeWidth=1;fontSize=12;fontStyle=1;fontColor=#92400E;fontFamily=Courier New;" value="Float" vertex="1">
<mxGeometry height="30" width="140" x="180" y="305" as="geometry" />
</mxCell>
<mxCell id="28" parent="1" style="rounded=0;whiteSpace=wrap;html=1;fillColor=#FFFBEB;strokeColor=#FDE68A;strokeWidth=1;fontSize=11;fontColor=#92400E;" value="Number → Object" vertex="1">
<mxGeometry height="30" width="200" x="320" y="305" as="geometry" />
</mxCell>
<mxCell id="29" parent="1" style="rounded=0;whiteSpace=wrap;html=1;fillColor=#F59E0B;strokeColor=#D97706;strokeWidth=1;fontSize=11;fontStyle=1;fontColor=#FFFFFF;" value="数值型" vertex="1">
<mxGeometry height="30" width="120" x="520" y="305" as="geometry" />
</mxCell>
<mxCell id="30" parent="1" style="rounded=0;whiteSpace=wrap;html=1;fillColor=#FEF3C7;strokeColor=#FDE68A;strokeWidth=1;fontSize=12;fontStyle=1;fontColor=#92400E;fontFamily=Courier New;" value="double" vertex="1">
<mxGeometry height="30" width="120" x="60" y="335" as="geometry" />
</mxCell>
<mxCell id="31" parent="1" style="rounded=0;whiteSpace=wrap;html=1;fillColor=#FFFBEB;strokeColor=#FDE68A;strokeWidth=1;fontSize=12;fontStyle=1;fontColor=#92400E;fontFamily=Courier New;" value="Double" vertex="1">
<mxGeometry height="30" width="140" x="180" y="335" as="geometry" />
</mxCell>
<mxCell id="32" parent="1" style="rounded=0;whiteSpace=wrap;html=1;fillColor=#FFFBEB;strokeColor=#FDE68A;strokeWidth=1;fontSize=11;fontColor=#92400E;" value="Number → Object" vertex="1">
<mxGeometry height="30" width="200" x="320" y="335" as="geometry" />
</mxCell>
<mxCell id="33" parent="1" style="rounded=0;whiteSpace=wrap;html=1;fillColor=#F59E0B;strokeColor=#D97706;strokeWidth=1;fontSize=11;fontStyle=1;fontColor=#FFFFFF;" value="数值型" vertex="1">
<mxGeometry height="30" width="120" x="520" y="335" as="geometry" />
</mxCell>
<mxCell id="34" parent="1" style="rounded=0;whiteSpace=wrap;html=1;fillColor=#DCFCE7;strokeColor=#BBF7D0;strokeWidth=1;fontSize=12;fontStyle=1;fontColor=#166534;fontFamily=Courier New;" value="char" vertex="1">
<mxGeometry height="30" width="120" x="60" y="365" as="geometry" />
</mxCell>
<mxCell id="35" parent="1" style="rounded=0;whiteSpace=wrap;html=1;fillColor=#F0FDF4;strokeColor=#BBF7D0;strokeWidth=1;fontSize=12;fontStyle=1;fontColor=#166534;fontFamily=Courier New;" value="Character" vertex="1">
<mxGeometry height="30" width="140" x="180" y="365" as="geometry" />
</mxCell>
<mxCell id="36" parent="1" style="rounded=0;whiteSpace=wrap;html=1;fillColor=#F0FDF4;strokeColor=#BBF7D0;strokeWidth=1;fontSize=11;fontColor=#166534;" value="Object" vertex="1">
<mxGeometry height="30" width="200" x="320" y="365" as="geometry" />
</mxCell>
<mxCell id="37" parent="1" style="rounded=0;whiteSpace=wrap;html=1;fillColor=#22C55E;strokeColor=#16A34A;strokeWidth=1;fontSize=11;fontStyle=1;fontColor=#FFFFFF;" value="字符型" vertex="1">
<mxGeometry height="30" width="120" x="520" y="365" as="geometry" />
</mxCell>
<mxCell id="38" parent="1" style="rounded=0;whiteSpace=wrap;html=1;fillColor=#F3E8FF;strokeColor=#E9D5FF;strokeWidth=1;fontSize=12;fontStyle=1;fontColor=#6D28D9;fontFamily=Courier New;" value="boolean" vertex="1">
<mxGeometry height="30" width="120" x="60" y="395" as="geometry" />
</mxCell>
<mxCell id="39" parent="1" style="rounded=0;whiteSpace=wrap;html=1;fillColor=#FAF5FF;strokeColor=#E9D5FF;strokeWidth=1;fontSize=12;fontStyle=1;fontColor=#6D28D9;fontFamily=Courier New;" value="Boolean" vertex="1">
<mxGeometry height="30" width="140" x="180" y="395" as="geometry" />
</mxCell>
<mxCell id="40" parent="1" style="rounded=0;whiteSpace=wrap;html=1;fillColor=#FAF5FF;strokeColor=#E9D5FF;strokeWidth=1;fontSize=11;fontColor=#6D28D9;" value="Object" vertex="1">
<mxGeometry height="30" width="200" x="320" y="395" as="geometry" />
</mxCell>
<mxCell id="41" parent="1" style="rounded=0;whiteSpace=wrap;html=1;fillColor=#8B5CF6;strokeColor=#7C3AED;strokeWidth=1;fontSize=11;fontStyle=1;fontColor=#FFFFFF;" value="布尔型" vertex="1">
<mxGeometry height="30" width="120" x="520" y="395" as="geometry" />
</mxCell>
<mxCell id="42" parent="1" style="rounded=1;whiteSpace=wrap;html=1;fillColor=#FFFFFF;strokeColor=#E2E8F0;strokeWidth=1;" value="" vertex="1">
<mxGeometry height="255" width="185" x="660" y="150" as="geometry" />
</mxCell>
<mxCell id="43" parent="1" style="text;html=1;strokeColor=none;fillColor=#1E293B;align=center;verticalAlign=middle;fontSize=11;fontStyle=1;fontColor=#FFFFFF;rounded=1;" value="💡 说明" vertex="1">
<mxGeometry height="22" width="60" x="675" y="160" as="geometry" />
</mxCell>
<mxCell id="44" parent="1" style="text;html=1;strokeColor=none;fillColor=#3B82F6;align=center;verticalAlign=middle;fontSize=10;fontStyle=1;fontColor=#FFFFFF;rounded=1;" value="6个数值类型" vertex="1">
<mxGeometry height="20" width="80" x="675" y="195" as="geometry" />
</mxCell>
<mxCell id="45" parent="1" style="text;html=1;strokeColor=none;fillColor=none;align=left;verticalAlign=middle;fontSize=10;fontColor=#475569;spacingLeft=5;" value="继承自 Number 类" vertex="1">
<mxGeometry height="18" width="120" x="675" y="220" as="geometry" />
</mxCell>
<mxCell id="46" parent="1" style="text;html=1;strokeColor=none;fillColor=#22C55E;align=center;verticalAlign=middle;fontSize=10;fontStyle=1;fontColor=#FFFFFF;rounded=1;" value="Character" vertex="1">
<mxGeometry height="20" width="70" x="675" y="250" as="geometry" />
</mxCell>
<mxCell id="47" parent="1" style="text;html=1;strokeColor=none;fillColor=none;align=left;verticalAlign=middle;fontSize=10;fontColor=#475569;spacingLeft=5;" value="直接继承 Object" vertex="1">
<mxGeometry height="18" width="110" x="675" y="275" as="geometry" />
</mxCell>
<mxCell id="48" parent="1" style="text;html=1;strokeColor=none;fillColor=#8B5CF6;align=center;verticalAlign=middle;fontSize=10;fontStyle=1;fontColor=#FFFFFF;rounded=1;" value="Boolean" vertex="1">
<mxGeometry height="20" width="60" x="675" y="305" as="geometry" />
</mxCell>
<mxCell id="49" parent="1" style="text;html=1;strokeColor=none;fillColor=none;align=left;verticalAlign=middle;fontSize=10;fontColor=#475569;spacingLeft=5;" value="直接继承 Object" vertex="1">
<mxGeometry height="18" width="110" x="675" y="330" as="geometry" />
</mxCell>
<mxCell id="50" parent="1" style="text;html=1;strokeColor=none;fillColor=#FEE2E2;align=center;verticalAlign=middle;fontSize=10;fontStyle=1;fontColor=#991B1B;rounded=1;" value="所有包装类都是 final" vertex="1">
<mxGeometry height="22" width="130" x="675" y="365" as="geometry" />
</mxCell>
<mxCell id="51" parent="1" style="text;html=1;strokeColor=none;fillColor=#22C55E;align=center;verticalAlign=middle;fontSize=14;fontStyle=1;fontColor=#FFFFFF;rounded=1;" value="🌳 继承层次结构" vertex="1">
<mxGeometry height="28" width="140" x="40" y="450" as="geometry" />
</mxCell>
<mxCell id="52" parent="1" style="rounded=1;whiteSpace=wrap;html=1;fillColor=#F0FDF4;strokeColor=#22C55E;strokeWidth=2;" value="" vertex="1">
<mxGeometry height="330" width="820" x="40" y="490" as="geometry" />
</mxCell>
<mxCell id="53" parent="1" style="rounded=1;whiteSpace=wrap;html=1;fillColor=#1E293B;strokeColor=#0F172A;strokeWidth=2;fontSize=16;fontStyle=1;fontColor=#FFFFFF;" value="Object" vertex="1">
<mxGeometry height="45" width="120" x="390" y="510" as="geometry" />
</mxCell>
<mxCell id="edge1" parent="1" style="edgeStyle=orthogonalEdgeStyle;rounded=0;orthogonalLoop=1;jettySize=auto;html=1;strokeColor=#64748B;strokeWidth=2;endArrow=block;endFill=0;endSize=10;" edge="1" source="53" target="59">
<mxGeometry relative="1" as="geometry">
<Array as="points">
<mxPoint x="450" y="575" />
<mxPoint x="340" y="575" />
</Array>
</mxGeometry>
</mxCell>
<mxCell id="edge2" parent="1" style="edgeStyle=orthogonalEdgeStyle;rounded=0;orthogonalLoop=1;jettySize=auto;html=1;strokeColor=#64748B;strokeWidth=2;endArrow=block;endFill=0;endSize=10;" edge="1" source="53" target="60">
<mxGeometry relative="1" as="geometry">
<Array as="points">
<mxPoint x="450" y="575" />
<mxPoint x="550" y="575" />
</Array>
</mxGeometry>
</mxCell>
<mxCell id="edge3" parent="1" style="edgeStyle=orthogonalEdgeStyle;rounded=0;orthogonalLoop=1;jettySize=auto;html=1;strokeColor=#64748B;strokeWidth=2;endArrow=block;endFill=0;endSize=10;" edge="1" source="53" target="61">
<mxGeometry relative="1" as="geometry">
<Array as="points">
<mxPoint x="450" y="575" />
<mxPoint x="730" y="575" />
</Array>
</mxGeometry>
</mxCell>
<mxCell id="59" parent="1" style="rounded=1;whiteSpace=wrap;html=1;fillColor=#3B82F6;strokeColor=#2563EB;strokeWidth=2;fontSize=14;fontStyle=1;fontColor=#FFFFFF;" value="Number
(abstract)" vertex="1">
<mxGeometry height="50" width="160" x="260" y="600" as="geometry" />
</mxCell>
<mxCell id="60" parent="1" style="rounded=1;whiteSpace=wrap;html=1;fillColor=#22C55E;strokeColor=#16A34A;strokeWidth=2;fontSize=14;fontStyle=1;fontColor=#FFFFFF;" value="Character" vertex="1">
<mxGeometry height="50" width="120" x="490" y="600" as="geometry" />
</mxCell>
<mxCell id="61" parent="1" style="rounded=1;whiteSpace=wrap;html=1;fillColor=#8B5CF6;strokeColor=#7C3AED;strokeWidth=2;fontSize=14;fontStyle=1;fontColor=#FFFFFF;" value="Boolean" vertex="1">
<mxGeometry height="50" width="120" x="670" y="600" as="geometry" />
</mxCell>
<mxCell id="line_num_main" parent="1" style="endArrow=none;html=1;strokeColor=#3B82F6;strokeWidth=2;" edge="1">
<mxGeometry relative="1" as="geometry">
<mxPoint x="340" y="650" as="sourcePoint" />
<mxPoint x="340" y="680" as="targetPoint" />
</mxGeometry>
</mxCell>
<mxCell id="line_num_cross" parent="1" style="endArrow=none;html=1;strokeColor=#3B82F6;strokeWidth=2;" edge="1">
<mxGeometry relative="1" as="geometry">
<mxPoint x="90" y="680" as="sourcePoint" />
<mxPoint x="590" y="680" as="targetPoint" />
</mxGeometry>
</mxCell>
<mxCell id="num1" parent="1" style="rounded=1;whiteSpace=wrap;html=1;fillColor=#EFF6FF;strokeColor=#BFDBFE;strokeWidth=2;fontSize=12;fontStyle=1;fontColor=#1E40AF;" value="Byte" vertex="1">
<mxGeometry height="40" width="80" x="50" y="710" as="geometry" />
</mxCell>
<mxCell id="edge_num1" parent="1" style="edgeStyle=orthogonalEdgeStyle;rounded=0;html=1;strokeColor=#3B82F6;strokeWidth=2;endArrow=block;endFill=0;endSize=8;" edge="1" target="num1">
<mxGeometry relative="1" as="geometry">
<mxPoint x="90" y="680" as="sourcePoint" />
</mxGeometry>
</mxCell>
<mxCell id="num2" parent="1" style="rounded=1;whiteSpace=wrap;html=1;fillColor=#EFF6FF;strokeColor=#BFDBFE;strokeWidth=2;fontSize=12;fontStyle=1;fontColor=#1E40AF;" value="Short" vertex="1">
<mxGeometry height="40" width="80" x="150" y="710" as="geometry" />
</mxCell>
<mxCell id="edge_num2" parent="1" style="edgeStyle=orthogonalEdgeStyle;rounded=0;html=1;strokeColor=#3B82F6;strokeWidth=2;endArrow=block;endFill=0;endSize=8;" edge="1" target="num2">
<mxGeometry relative="1" as="geometry">
<mxPoint x="190" y="680" as="sourcePoint" />
</mxGeometry>
</mxCell>
<mxCell id="num3" parent="1" style="rounded=1;whiteSpace=wrap;html=1;fillColor=#EFF6FF;strokeColor=#BFDBFE;strokeWidth=2;fontSize=12;fontStyle=1;fontColor=#1E40AF;" value="Integer" vertex="1">
<mxGeometry height="40" width="80" x="250" y="710" as="geometry" />
</mxCell>
<mxCell id="edge_num3" parent="1" style="edgeStyle=orthogonalEdgeStyle;rounded=0;html=1;strokeColor=#3B82F6;strokeWidth=2;endArrow=block;endFill=0;endSize=8;" edge="1" target="num3">
<mxGeometry relative="1" as="geometry">
<mxPoint x="290" y="680" as="sourcePoint" />
</mxGeometry>
</mxCell>
<mxCell id="num4" parent="1" style="rounded=1;whiteSpace=wrap;html=1;fillColor=#EFF6FF;strokeColor=#BFDBFE;strokeWidth=2;fontSize=12;fontStyle=1;fontColor=#1E40AF;" value="Long" vertex="1">
<mxGeometry height="40" width="80" x="350" y="710" as="geometry" />
</mxCell>
<mxCell id="edge_num4" parent="1" style="edgeStyle=orthogonalEdgeStyle;rounded=0;html=1;strokeColor=#3B82F6;strokeWidth=2;endArrow=block;endFill=0;endSize=8;" edge="1" target="num4">
<mxGeometry relative="1" as="geometry">
<mxPoint x="390" y="680" as="sourcePoint" />
</mxGeometry>
</mxCell>
<mxCell id="num5" parent="1" style="rounded=1;whiteSpace=wrap;html=1;fillColor=#FFFBEB;strokeColor=#FDE68A;strokeWidth=2;fontSize=12;fontStyle=1;fontColor=#92400E;" value="Float" vertex="1">
<mxGeometry height="40" width="80" x="450" y="710" as="geometry" />
</mxCell>
<mxCell id="edge_num5" parent="1" style="edgeStyle=orthogonalEdgeStyle;rounded=0;html=1;strokeColor=#3B82F6;strokeWidth=2;endArrow=block;endFill=0;endSize=8;" edge="1" target="num5">
<mxGeometry relative="1" as="geometry">
<mxPoint x="490" y="680" as="sourcePoint" />
</mxGeometry>
</mxCell>
<mxCell id="num6" parent="1" style="rounded=1;whiteSpace=wrap;html=1;fillColor=#FFFBEB;strokeColor=#FDE68A;strokeWidth=2;fontSize=12;fontStyle=1;fontColor=#92400E;" value="Double" vertex="1">
<mxGeometry height="40" width="80" x="550" y="710" as="geometry" />
</mxCell>
<mxCell id="edge_num6" parent="1" style="edgeStyle=orthogonalEdgeStyle;rounded=0;html=1;strokeColor=#3B82F6;strokeWidth=2;endArrow=block;endFill=0;endSize=8;" edge="1" target="num6">
<mxGeometry relative="1" as="geometry">
<mxPoint x="590" y="680" as="sourcePoint" />
</mxGeometry>
</mxCell>
</root>
</mxGraphModel>
</diagram>
</mxfile>
7.2 基本类型与包装类的区别
<mxfile>
<diagram id="primitive-vs-wrapper" name="基本类型 vs 包装类型">
<mxGraphModel dx="926" dy="817" grid="1" gridSize="10" guides="1" tooltips="1" connect="1" arrows="1" fold="1" page="1" pageScale="1" pageWidth="900" pageHeight="750" math="0" shadow="0">
<root>
<mxCell id="0" />
<mxCell id="1" parent="0" />
<mxCell id="2" parent="1" style="rounded=1;whiteSpace=wrap;html=1;fillColor=#fafafa;strokeColor=#5c6bc0;strokeWidth=3;shadow=1;" value="" vertex="1">
<mxGeometry height="720" width="820" x="40" y="20" as="geometry" />
</mxCell>
<mxCell id="3" parent="1" style="text;html=1;strokeColor=none;fillColor=none;align=center;verticalAlign=middle;whiteSpace=wrap;rounded=0;fontSize=26;fontStyle=1;fontColor=#1a237e;" value="基本类型 vs 包装类型" vertex="1">
<mxGeometry height="50" width="400" x="250" y="40" as="geometry" />
</mxCell>
<mxCell id="4" parent="1" style="rounded=1;whiteSpace=wrap;html=1;fillColor=#3949ab;strokeColor=none;arcSize=8;" value="" vertex="1">
<mxGeometry height="55" width="760" x="70" y="105" as="geometry" />
</mxCell>
<mxCell id="5" parent="1" style="text;html=1;strokeColor=none;fillColor=none;align=center;verticalAlign=middle;whiteSpace=wrap;rounded=0;fontSize=17;fontStyle=1;fontColor=#ffffff;" value="对比项" vertex="1">
<mxGeometry height="55" width="160" x="70" y="105" as="geometry" />
</mxCell>
<mxCell id="6" parent="1" style="text;html=1;strokeColor=none;fillColor=none;align=center;verticalAlign=middle;whiteSpace=wrap;rounded=0;fontSize=17;fontStyle=1;fontColor=#ffffff;" value="基本类型" vertex="1">
<mxGeometry height="55" width="250" x="230" y="105" as="geometry" />
</mxCell>
<mxCell id="7" parent="1" style="text;html=1;strokeColor=none;fillColor=none;align=center;verticalAlign=middle;whiteSpace=wrap;rounded=0;fontSize=17;fontStyle=1;fontColor=#ffffff;" value="包装类型" vertex="1">
<mxGeometry height="55" width="350" x="480" y="105" as="geometry" />
</mxCell>
<mxCell id="8" edge="1" parent="1" style="endArrow=none;html=1;strokeColor=#e0e0e0;strokeWidth=2;" value="">
<mxGeometry height="50" relative="1" width="50" as="geometry">
<mxPoint x="230" y="160" as="sourcePoint" />
<mxPoint x="230" y="690" as="targetPoint" />
</mxGeometry>
</mxCell>
<mxCell id="9" edge="1" parent="1" style="endArrow=none;html=1;strokeColor=#e0e0e0;strokeWidth=2;" value="">
<mxGeometry height="50" relative="1" width="50" as="geometry">
<mxPoint x="480" y="160" as="sourcePoint" />
<mxPoint x="480" y="690" as="targetPoint" />
</mxGeometry>
</mxCell>
<mxCell id="10" parent="1" style="rounded=0;whiteSpace=wrap;html=1;fillColor=#e3f2fd;strokeColor=none;" value="" vertex="1">
<mxGeometry height="55" width="760" x="70" y="160" as="geometry" />
</mxCell>
<mxCell id="11" parent="1" style="text;html=1;strokeColor=none;fillColor=none;align=center;verticalAlign=middle;whiteSpace=wrap;rounded=0;fontSize=14;fontStyle=1;fontColor=#1565c0;" value="存储内容" vertex="1">
<mxGeometry height="55" width="160" x="70" y="160" as="geometry" />
</mxCell>
<mxCell id="12" parent="1" style="text;html=1;strokeColor=none;fillColor=none;align=center;verticalAlign=middle;whiteSpace=wrap;rounded=0;fontSize=14;" value="直接存储值" vertex="1">
<mxGeometry height="55" width="250" x="230" y="160" as="geometry" />
</mxCell>
<mxCell id="13" parent="1" style="text;html=1;strokeColor=none;fillColor=none;align=center;verticalAlign=middle;whiteSpace=wrap;rounded=0;fontSize=14;" value="存储对象引用" vertex="1">
<mxGeometry height="55" width="350" x="480" y="160" as="geometry" />
</mxCell>
<mxCell id="14" parent="1" style="rounded=0;whiteSpace=wrap;html=1;fillColor=#ffffff;strokeColor=none;" value="" vertex="1">
<mxGeometry height="70" width="760" x="70" y="215" as="geometry" />
</mxCell>
<mxCell id="15" parent="1" style="text;html=1;strokeColor=none;fillColor=none;align=center;verticalAlign=middle;whiteSpace=wrap;rounded=0;fontSize=14;fontStyle=1;fontColor=#1565c0;" value="存储位置" vertex="1">
<mxGeometry height="70" width="160" x="70" y="215" as="geometry" />
</mxCell>
<mxCell id="16" parent="1" style="text;html=1;strokeColor=none;fillColor=none;align=center;verticalAlign=middle;whiteSpace=wrap;rounded=0;fontSize=14;" value="<font color="#2e7d32">栈</font>（局部变量）<br><font color="#1565c0">堆</font>（成员变量）" vertex="1">
<mxGeometry height="70" width="250" x="230" y="215" as="geometry" />
</mxCell>
<mxCell id="17" parent="1" style="text;html=1;strokeColor=none;fillColor=none;align=center;verticalAlign=middle;whiteSpace=wrap;rounded=0;fontSize=14;" value="<font color="#1565c0">堆</font>（对象本身）<br><font color="#2e7d32">栈</font>/<font color="#1565c0">堆</font>（引用）" vertex="1">
<mxGeometry height="70" width="350" x="480" y="215" as="geometry" />
</mxCell>
<mxCell id="18" parent="1" style="rounded=0;whiteSpace=wrap;html=1;fillColor=#e3f2fd;strokeColor=none;" value="" vertex="1">
<mxGeometry height="55" width="760" x="70" y="285" as="geometry" />
</mxCell>
<mxCell id="19" parent="1" style="text;html=1;strokeColor=none;fillColor=none;align=center;verticalAlign=middle;whiteSpace=wrap;rounded=0;fontSize=14;fontStyle=1;fontColor=#1565c0;" value="默认值" vertex="1">
<mxGeometry height="55" width="160" x="70" y="285" as="geometry" />
</mxCell>
<mxCell id="20" parent="1" style="rounded=1;whiteSpace=wrap;html=1;fillColor=#c8e6c9;strokeColor=#4caf50;" value="" vertex="1">
<mxGeometry height="30" width="160" x="275" y="297" as="geometry" />
</mxCell>
<mxCell id="21" parent="1" style="text;html=1;strokeColor=none;fillColor=none;align=center;verticalAlign=middle;whiteSpace=wrap;rounded=0;fontSize=13;fontColor=#2e7d32;" value="<font face="Courier New">0 / 0.0 / false</font>" vertex="1">
<mxGeometry height="30" width="160" x="275" y="297" as="geometry" />
</mxCell>
<mxCell id="22" parent="1" style="rounded=1;whiteSpace=wrap;html=1;fillColor=#ffcdd2;strokeColor=#e57373;" value="" vertex="1">
<mxGeometry height="30" width="100" x="595" y="297" as="geometry" />
</mxCell>
<mxCell id="23" parent="1" style="text;html=1;strokeColor=none;fillColor=none;align=center;verticalAlign=middle;whiteSpace=wrap;rounded=0;fontSize=13;fontColor=#c62828;" value="<font face="Courier New">null</font>" vertex="1">
<mxGeometry height="30" width="100" x="595" y="297" as="geometry" />
</mxCell>
<mxCell id="24" parent="1" style="rounded=0;whiteSpace=wrap;html=1;fillColor=#ffffff;strokeColor=none;" value="" vertex="1">
<mxGeometry height="70" width="760" x="70" y="340" as="geometry" />
</mxCell>
<mxCell id="25" parent="1" style="text;html=1;strokeColor=none;fillColor=none;align=center;verticalAlign=middle;whiteSpace=wrap;rounded=0;fontSize=14;fontStyle=1;fontColor=#1565c0;" value="空间占用" vertex="1">
<mxGeometry height="70" width="160" x="70" y="340" as="geometry" />
</mxCell>
<mxCell id="26" parent="1" style="text;html=1;strokeColor=none;fillColor=none;align=center;verticalAlign=middle;whiteSpace=wrap;rounded=0;fontSize=14;" value="固定大小<br><font color="#757575">(1~8 字节)</font>" vertex="1">
<mxGeometry height="70" width="250" x="230" y="340" as="geometry" />
</mxCell>
<mxCell id="27" parent="1" style="text;html=1;strokeColor=none;fillColor=none;align=center;verticalAlign=middle;whiteSpace=wrap;rounded=0;fontSize=14;" value="对象头 + 值 + 对齐填充<br><font color="#757575">(至少 16 字节)</font>" vertex="1">
<mxGeometry height="70" width="350" x="480" y="340" as="geometry" />
</mxCell>
<mxCell id="28" parent="1" style="rounded=0;whiteSpace=wrap;html=1;fillColor=#e3f2fd;strokeColor=none;" value="" vertex="1">
<mxGeometry height="70" width="760" x="70" y="410" as="geometry" />
</mxCell>
<mxCell id="29" parent="1" style="text;html=1;strokeColor=none;fillColor=none;align=center;verticalAlign=middle;whiteSpace=wrap;rounded=0;fontSize=14;fontStyle=1;fontColor=#1565c0;" value="比较方式" vertex="1">
<mxGeometry height="70" width="160" x="70" y="410" as="geometry" />
</mxCell>
<mxCell id="30" parent="1" style="rounded=1;whiteSpace=wrap;html=1;fillColor=#e8f5e9;strokeColor=#81c784;" value="" vertex="1">
<mxGeometry height="30" width="150" x="280" y="430" as="geometry" />
</mxCell>
<mxCell id="31" parent="1" style="text;html=1;strokeColor=none;fillColor=none;align=center;verticalAlign=middle;whiteSpace=wrap;rounded=0;fontSize=13;" value="<font face="Courier New">==</font> 比较值" vertex="1">
<mxGeometry height="30" width="150" x="280" y="430" as="geometry" />
</mxCell>
<mxCell id="32" parent="1" style="text;html=1;strokeColor=none;fillColor=none;align=center;verticalAlign=middle;whiteSpace=wrap;rounded=0;fontSize=13;" value="<font face="Courier New">==</font> 比较地址<br><font face="Courier New">equals()</font> 比较值" vertex="1">
<mxGeometry height="70" width="350" x="480" y="410" as="geometry" />
</mxCell>
<mxCell id="33" parent="1" style="rounded=0;whiteSpace=wrap;html=1;fillColor=#ffffff;strokeColor=none;" value="" vertex="1">
<mxGeometry height="55" width="760" x="70" y="480" as="geometry" />
</mxCell>
<mxCell id="34" parent="1" style="text;html=1;strokeColor=none;fillColor=none;align=center;verticalAlign=middle;whiteSpace=wrap;rounded=0;fontSize=14;fontStyle=1;fontColor=#1565c0;" value="泛型支持" vertex="1">
<mxGeometry height="55" width="160" x="70" y="480" as="geometry" />
</mxCell>
<mxCell id="35" parent="1" style="rounded=1;whiteSpace=wrap;html=1;fillColor=#ffcdd2;strokeColor=#e57373;" value="" vertex="1">
<mxGeometry height="30" width="120" x="295" y="492" as="geometry" />
</mxCell>
<mxCell id="36" parent="1" style="text;html=1;strokeColor=none;fillColor=none;align=center;verticalAlign=middle;whiteSpace=wrap;rounded=0;fontSize=13;fontColor=#c62828;" value="❌ 不支持" vertex="1">
<mxGeometry height="30" width="120" x="295" y="492" as="geometry" />
</mxCell>
<mxCell id="37" parent="1" style="rounded=1;whiteSpace=wrap;html=1;fillColor=#c8e6c9;strokeColor=#81c784;" value="" vertex="1">
<mxGeometry height="30" width="120" x="595" y="492" as="geometry" />
</mxCell>
<mxCell id="38" parent="1" style="text;html=1;strokeColor=none;fillColor=none;align=center;verticalAlign=middle;whiteSpace=wrap;rounded=0;fontSize=13;fontColor=#2e7d32;" value="✅ 支持" vertex="1">
<mxGeometry height="30" width="120" x="595" y="492" as="geometry" />
</mxCell>
<mxCell id="39" parent="1" style="rounded=0;whiteSpace=wrap;html=1;fillColor=#e3f2fd;strokeColor=none;" value="" vertex="1">
<mxGeometry height="55" width="760" x="70" y="535" as="geometry" />
</mxCell>
<mxCell id="40" parent="1" style="text;html=1;strokeColor=none;fillColor=none;align=center;verticalAlign=middle;whiteSpace=wrap;rounded=0;fontSize=14;fontStyle=1;fontColor=#1565c0;" value="集合使用" vertex="1">
<mxGeometry height="55" width="160" x="70" y="535" as="geometry" />
</mxCell>
<mxCell id="41" parent="1" style="rounded=1;whiteSpace=wrap;html=1;fillColor=#ffcdd2;strokeColor=#e57373;" value="" vertex="1">
<mxGeometry height="30" width="160" x="275" y="547" as="geometry" />
</mxCell>
<mxCell id="42" parent="1" style="text;html=1;strokeColor=none;fillColor=none;align=center;verticalAlign=middle;whiteSpace=wrap;rounded=0;fontSize=13;fontColor=#c62828;" value="❌ 不能放入集合" vertex="1">
<mxGeometry height="30" width="160" x="275" y="547" as="geometry" />
</mxCell>
<mxCell id="43" parent="1" style="rounded=1;whiteSpace=wrap;html=1;fillColor=#c8e6c9;strokeColor=#81c784;" value="" vertex="1">
<mxGeometry height="30" width="160" x="575" y="547" as="geometry" />
</mxCell>
<mxCell id="44" parent="1" style="text;html=1;strokeColor=none;fillColor=none;align=center;verticalAlign=middle;whiteSpace=wrap;rounded=0;fontSize=13;fontColor=#2e7d32;" value="✅ 可以放入集合" vertex="1">
<mxGeometry height="30" width="160" x="575" y="547" as="geometry" />
</mxCell>
<mxCell id="45" parent="1" style="rounded=0;whiteSpace=wrap;html=1;fillColor=#ffffff;strokeColor=none;" value="" vertex="1">
<mxGeometry height="55" width="760" x="70" y="590" as="geometry" />
</mxCell>
<mxCell id="46" parent="1" style="text;html=1;strokeColor=none;fillColor=none;align=center;verticalAlign=middle;whiteSpace=wrap;rounded=0;fontSize=14;fontStyle=1;fontColor=#1565c0;" value="空值表示" vertex="1">
<mxGeometry height="55" width="160" x="70" y="590" as="geometry" />
</mxCell>
<mxCell id="47" parent="1" style="rounded=1;whiteSpace=wrap;html=1;fillColor=#ffcdd2;strokeColor=#e57373;" value="" vertex="1">
<mxGeometry height="30" width="150" x="280" y="602" as="geometry" />
</mxCell>
<mxCell id="48" parent="1" style="text;html=1;strokeColor=none;fillColor=none;align=center;verticalAlign=middle;whiteSpace=wrap;rounded=0;fontSize=13;fontColor=#c62828;" value="❌ 无法表示空" vertex="1">
<mxGeometry height="30" width="150" x="280" y="602" as="geometry" />
</mxCell>
<mxCell id="49" parent="1" style="rounded=1;whiteSpace=wrap;html=1;fillColor=#c8e6c9;strokeColor=#81c784;" value="" vertex="1">
<mxGeometry height="30" width="150" x="580" y="602" as="geometry" />
</mxCell>
<mxCell id="50" parent="1" style="text;html=1;strokeColor=none;fillColor=none;align=center;verticalAlign=middle;whiteSpace=wrap;rounded=0;fontSize=13;fontColor=#2e7d32;" value="✅ 可以为 null" vertex="1">
<mxGeometry height="30" width="150" x="580" y="602" as="geometry" />
</mxCell>
<mxCell id="51" parent="1" style="rounded=1;whiteSpace=wrap;html=1;fillColor=#fff3e0;strokeColor=#ff9800;strokeWidth=2;" value="" vertex="1">
<mxGeometry height="40" width="760" x="70" y="660" as="geometry" />
</mxCell>
<mxCell id="52" parent="1" style="text;html=1;strokeColor=none;fillColor=none;align=center;verticalAlign=middle;whiteSpace=wrap;rounded=0;fontSize=13;fontColor=#e65100;fontStyle=1;" value="💡 选择建议：性能敏感用基本类型，需要对象特性（泛型/集合/null）用包装类型" vertex="1">
<mxGeometry height="40" width="760" x="70" y="660" as="geometry" />
</mxCell>
</root>
</mxGraphModel>
</diagram>
</mxfile>
public class WrapperDemo {
public static void main(String[] args) {
// ═══════════════════════════════════════════════════════════════
// 默认值差异
// ═══════════════════════════════════════════════════════════════
int primitiveInt; // 局部变量必须初始化
Integer wrapperInt = null; // 可以为 null
// ═══════════════════════════════════════════════════════════════
// 比较方式差异
// ═══════════════════════════════════════════════════════════════
int a = 100;
int b = 100;
System.out.println(a == b); // true，比较值
Integer c = 200;
Integer d = 200;
System.out.println(c == d); // false，比较地址
System.out.println(c.equals(d)); // true，比较值
// ═══════════════════════════════════════════════════════════════
// 泛型与集合
// ═══════════════════════════════════════════════════════════════
// List<int> list; // ❌ 编译错误
List<Integer> list = new ArrayList<>(); // ✅ 正确
list.add(1); // 自动装箱
// ═══════════════════════════════════════════════════════════════
// 空值表示场景
// ═══════════════════════════════════════════════════════════════
// 数据库查询结果可能为 null
Integer score = getScoreFromDB(); // 可能返回 null
if (score == null) {
System.out.println("成绩未录入");
}
}
}
7.3 自动装箱与拆箱
<mxfile>
<diagram id="autoboxing-unboxing" name="自动装箱与拆箱">
<mxGraphModel dx="1111" dy="980" grid="1" gridSize="10" guides="1" tooltips="1" connect="1" arrows="1" fold="1" page="1" pageScale="1" pageWidth="900" pageHeight="680" math="0" shadow="0">
<root>
<mxCell id="0" />
<mxCell id="1" parent="0" />
<mxCell id="2" parent="1" style="rounded=1;whiteSpace=wrap;html=1;fillColor=#fafafa;strokeColor=#5c6bc0;strokeWidth=3;shadow=1;" value="" vertex="1">
<mxGeometry height="680" width="820" x="40" y="20" as="geometry" />
</mxCell>
<mxCell id="3" parent="1" style="text;html=1;strokeColor=none;fillColor=none;align=center;verticalAlign=middle;whiteSpace=wrap;rounded=0;fontSize=28;fontStyle=1;fontColor=#1a237e;" value="自动装箱与拆箱" vertex="1">
<mxGeometry height="50" width="340" x="280" y="40" as="geometry" />
</mxCell>
<mxCell id="4" parent="1" style="rounded=1;whiteSpace=wrap;html=1;fillColor=#e3f2fd;strokeColor=#1976d2;strokeWidth=2;" value="" vertex="1">
<mxGeometry height="245" width="780" x="60" y="105" as="geometry" />
</mxCell>
<mxCell id="5" parent="1" style="rounded=1;whiteSpace=wrap;html=1;fillColor=#1976d2;strokeColor=none;" value="" vertex="1">
<mxGeometry height="45" width="780" x="60" y="105" as="geometry" />
</mxCell>
<mxCell id="6" parent="1" style="text;html=1;strokeColor=none;fillColor=none;align=center;verticalAlign=middle;whiteSpace=wrap;rounded=0;fontSize=18;fontStyle=1;fontColor=#ffffff;" value="📦 装箱 (Boxing)：基本类型 → 包装类型" vertex="1">
<mxGeometry height="45" width="780" x="60" y="105" as="geometry" />
</mxCell>
<mxCell id="7" parent="1" style="rounded=1;whiteSpace=wrap;html=1;fillColor=#4caf50;strokeColor=none;shadow=1;" value="" vertex="1">
<mxGeometry height="60" width="140" x="90" y="170" as="geometry" />
</mxCell>
<mxCell id="8" parent="1" style="text;html=1;strokeColor=none;fillColor=none;align=center;verticalAlign=middle;whiteSpace=wrap;rounded=0;fontSize=13;" value="<font color="#ffffff"><b>基本类型</b><br><font face="Courier New">int value = 100</font></font>" vertex="1">
<mxGeometry height="60" width="140" x="90" y="170" as="geometry" />
</mxCell>
<mxCell id="9" edge="1" parent="1" style="endArrow=classic;html=1;strokeColor=#1976d2;strokeWidth=3;flowAnimation=1;" value="">
<mxGeometry height="50" relative="1" width="50" as="geometry">
<mxPoint x="230" y="200" as="sourcePoint" />
<mxPoint x="290" y="200" as="targetPoint" />
</mxGeometry>
</mxCell>
<mxCell id="10" parent="1" style="text;html=1;strokeColor=none;fillColor=none;align=center;verticalAlign=middle;whiteSpace=wrap;rounded=0;fontSize=11;fontColor=#1976d2;fontStyle=1;" value="自动装箱" vertex="1">
<mxGeometry height="20" width="60" x="230" y="175" as="geometry" />
</mxCell>
<mxCell id="11" parent="1" style="rounded=1;whiteSpace=wrap;html=1;fillColor=#ff9800;strokeColor=none;shadow=1;" value="" vertex="1">
<mxGeometry height="60" width="180" x="290" y="170" as="geometry" />
</mxCell>
<mxCell id="12" parent="1" style="text;html=1;strokeColor=none;fillColor=none;align=center;verticalAlign=middle;whiteSpace=wrap;rounded=0;fontSize=13;" value="<font color="#ffffff"><b>赋值语句</b><br><font face="Courier New">Integer obj = value;</font></font>" vertex="1">
<mxGeometry height="60" width="180" x="290" y="170" as="geometry" />
</mxCell>
<mxCell id="13" edge="1" parent="1" style="endArrow=classic;html=1;strokeColor=#1976d2;strokeWidth=3;flowAnimation=1;" value="">
<mxGeometry height="50" relative="1" width="50" as="geometry">
<mxPoint x="470" y="200" as="sourcePoint" />
<mxPoint x="530" y="200" as="targetPoint" />
</mxGeometry>
</mxCell>
<mxCell id="14" parent="1" style="text;html=1;strokeColor=none;fillColor=none;align=center;verticalAlign=middle;whiteSpace=wrap;rounded=0;fontSize=11;fontColor=#1976d2;fontStyle=1;" value="编译转换" vertex="1">
<mxGeometry height="20" width="60" x="470" y="175" as="geometry" />
</mxCell>
<mxCell id="15" parent="1" style="rounded=1;whiteSpace=wrap;html=1;fillColor=#7b1fa2;strokeColor=none;shadow=1;" value="" vertex="1">
<mxGeometry height="60" width="290" x="530" y="170" as="geometry" />
</mxCell>
<mxCell id="16" parent="1" style="text;html=1;strokeColor=none;fillColor=none;align=center;verticalAlign=middle;whiteSpace=wrap;rounded=0;fontSize=13;" value="<font color="#ffffff"><b>包装类型</b><br><font face="Courier New">Integer obj = Integer.valueOf(value);</font></font>" vertex="1">
<mxGeometry height="60" width="290" x="530" y="170" as="geometry" />
</mxCell>
<mxCell id="17" parent="1" style="rounded=1;whiteSpace=wrap;html=1;fillColor=#ffffff;strokeColor=#90caf9;strokeWidth=2;" value="" vertex="1">
<mxGeometry height="85" width="730" x="90" y="250" as="geometry" />
</mxCell>
<mxCell id="18" parent="1" style="text;html=1;strokeColor=none;fillColor=none;align=left;verticalAlign=middle;whiteSpace=wrap;rounded=0;fontSize=14;spacingLeft=15;" value="<div style="text-align: left;"><font face="Courier New"><font color="#9e9e9e">// 源代码</font><br><font color="#0d47a1">int</font> value = <font color="#e65100">100</font>;<br><font color="#7b1fa2">Integer</font> obj = value;&nbsp; <font color="#9e9e9e">// 自动装箱 → 编译后: Integer.valueOf(value)</font></div>" vertex="1">
<mxGeometry height="85" width="730" x="90" y="250" as="geometry" />
</mxCell>
<mxCell id="19" parent="1" style="rounded=1;whiteSpace=wrap;html=1;fillColor=#fce4ec;strokeColor=#c2185b;strokeWidth=2;" value="" vertex="1">
<mxGeometry height="245" width="780" x="60" y="370" as="geometry" />
</mxCell>
<mxCell id="20" parent="1" style="rounded=1;whiteSpace=wrap;html=1;fillColor=#c2185b;strokeColor=none;" value="" vertex="1">
<mxGeometry height="45" width="780" x="60" y="370" as="geometry" />
</mxCell>
<mxCell id="21" parent="1" style="text;html=1;strokeColor=none;fillColor=none;align=center;verticalAlign=middle;whiteSpace=wrap;rounded=0;fontSize=18;fontStyle=1;fontColor=#ffffff;" value="📤 拆箱 (Unboxing)：包装类型 → 基本类型" vertex="1">
<mxGeometry height="45" width="780" x="60" y="370" as="geometry" />
</mxCell>
<mxCell id="22" parent="1" style="rounded=1;whiteSpace=wrap;html=1;fillColor=#7b1fa2;strokeColor=none;shadow=1;" value="" vertex="1">
<mxGeometry height="60" width="200" x="90" y="435" as="geometry" />
</mxCell>
<mxCell id="23" parent="1" style="text;html=1;strokeColor=none;fillColor=none;align=center;verticalAlign=middle;whiteSpace=wrap;rounded=0;fontSize=13;" value="<font color="#ffffff"><b>包装类型</b><br><font face="Courier New">Integer obj = ...</font></font>" vertex="1">
<mxGeometry height="60" width="200" x="90" y="435" as="geometry" />
</mxCell>
<mxCell id="24" edge="1" parent="1" style="endArrow=classic;html=1;strokeColor=#c2185b;strokeWidth=3;flowAnimation=1;" value="">
<mxGeometry height="50" relative="1" width="50" as="geometry">
<mxPoint x="290" y="465" as="sourcePoint" />
<mxPoint x="350" y="465" as="targetPoint" />
</mxGeometry>
</mxCell>
<mxCell id="25" parent="1" style="text;html=1;strokeColor=none;fillColor=none;align=center;verticalAlign=middle;whiteSpace=wrap;rounded=0;fontSize=11;fontColor=#c2185b;fontStyle=1;" value="自动拆箱" vertex="1">
<mxGeometry height="20" width="60" x="290" y="440" as="geometry" />
</mxCell>
<mxCell id="26" parent="1" style="rounded=1;whiteSpace=wrap;html=1;fillColor=#ff9800;strokeColor=none;shadow=1;" value="" vertex="1">
<mxGeometry height="60" width="170" x="350" y="435" as="geometry" />
</mxCell>
<mxCell id="27" parent="1" style="text;html=1;strokeColor=none;fillColor=none;align=center;verticalAlign=middle;whiteSpace=wrap;rounded=0;fontSize=13;" value="<font color="#ffffff"><b>赋值语句</b><br><font face="Courier New">int value = obj;</font></font>" vertex="1">
<mxGeometry height="60" width="170" x="350" y="435" as="geometry" />
</mxCell>
<mxCell id="28" edge="1" parent="1" style="endArrow=classic;html=1;strokeColor=#c2185b;strokeWidth=3;flowAnimation=1;" value="">
<mxGeometry height="50" relative="1" width="50" as="geometry">
<mxPoint x="520" y="465" as="sourcePoint" />
<mxPoint x="580" y="465" as="targetPoint" />
</mxGeometry>
</mxCell>
<mxCell id="29" parent="1" style="text;html=1;strokeColor=none;fillColor=none;align=center;verticalAlign=middle;whiteSpace=wrap;rounded=0;fontSize=11;fontColor=#c2185b;fontStyle=1;" value="编译转换" vertex="1">
<mxGeometry height="20" width="60" x="520" y="440" as="geometry" />
</mxCell>
<mxCell id="30" parent="1" style="rounded=1;whiteSpace=wrap;html=1;fillColor=#4caf50;strokeColor=none;shadow=1;" value="" vertex="1">
<mxGeometry height="60" width="240" x="580" y="435" as="geometry" />
</mxCell>
<mxCell id="31" parent="1" style="text;html=1;strokeColor=none;fillColor=none;align=center;verticalAlign=middle;whiteSpace=wrap;rounded=0;fontSize=13;" value="<font color="#ffffff"><b>基本类型</b><br><font face="Courier New">int value = obj.intValue();</font></font>" vertex="1">
<mxGeometry height="60" width="240" x="580" y="435" as="geometry" />
</mxCell>
<mxCell id="32" parent="1" style="rounded=1;whiteSpace=wrap;html=1;fillColor=#ffffff;strokeColor=#f48fb1;strokeWidth=2;" value="" vertex="1">
<mxGeometry height="85" width="730" x="90" y="515" as="geometry" />
</mxCell>
<mxCell id="33" parent="1" style="text;html=1;strokeColor=none;fillColor=none;align=left;verticalAlign=middle;whiteSpace=wrap;rounded=0;fontSize=14;spacingLeft=15;" value="<div style="text-align: left;"><font face="Courier New"><font color="#9e9e9e">// 源代码</font><br><font color="#7b1fa2">Integer</font> obj = <font color="#7b1fa2">Integer</font>.valueOf(<font color="#e65100">100</font>);<br><font color="#0d47a1">int</font> value = obj;&nbsp; <font color="#9e9e9e">// 自动拆箱 → 编译后: obj.intValue()</font></font></div>" vertex="1">
<mxGeometry height="85" width="730" x="90" y="515" as="geometry" />
</mxCell>
<mxCell id="34" parent="1" style="rounded=1;whiteSpace=wrap;html=1;fillColor=#fff8e1;strokeColor=#ffa000;strokeWidth=2;" value="" vertex="1">
<mxGeometry height="30" width="780" x="60" y="625" as="geometry" />
</mxCell>
<mxCell id="35" parent="1" style="text;html=1;strokeColor=none;fillColor=none;align=center;verticalAlign=middle;whiteSpace=wrap;rounded=0;fontSize=13;fontColor=#e65100;fontStyle=1;" value="💡 自动装箱/拆箱是编译器的语法糖，运行时仍调用 valueOf() 和 xxxValue() 方法" vertex="1">
<mxGeometry height="30" width="780" x="60" y="625" as="geometry" />
</mxCell>
</root>
</mxGraphModel>
</diagram>
</mxfile>
public class BoxingDemo {
public static void main(String[] args) {
// ═══════════════════════════════════════════════════════════════
// 自动装箱
// ═══════════════════════════════════════════════════════════════
Integer a = 100; // Integer.valueOf(100)
Double b = 3.14; // Double.valueOf(3.14)
Boolean c = true; // Boolean.valueOf(true)
// ═══════════════════════════════════════════════════════════════
// 自动拆箱
// ═══════════════════════════════════════════════════════════════
int x = a; // a.intValue()
double y = b; // b.doubleValue()
boolean z = c; // c.booleanValue()
// ═══════════════════════════════════════════════════════════════
// 运算中的自动拆箱
// ═══════════════════════════════════════════════════════════════
Integer num1 = 10;
Integer num2 = 20;
int sum = num1 + num2; // 先拆箱再相加
// 等价于:
// int sum = num1.intValue() + num2.intValue();
// ═══════════════════════════════════════════════════════════════
// 比较中的陷阱
// ═══════════════════════════════════════════════════════════════
Integer i1 = 100;
Integer i2 = 100;
Integer i3 = 200;
Integer i4 = 200;
System.out.println(i1 == i2); // true (缓存)
System.out.println(i3 == i4); // false (超出缓存)
// 与基本类型比较时会自动拆箱
int p = 100;
System.out.println(i1 == p); // true (i1 拆箱后比较值)
}
}
自动拆箱的 NPE 陷阱：
public class NullPointerDemo {
public static void main(String[] args) {
// ═══════════════════════════════════════════════════════════════
// 拆箱 null 会抛出 NullPointerException
// ═══════════════════════════════════════════════════════════════
Integer num = null;
// int value = num; // ❌ NullPointerException
// 等价于: int value = num.intValue(); // null.intValue() 报错
// 安全写法
int value = (num != null) ? num : 0;
// 或 JDK 9+
int value2 = Objects.requireNonNullElse(num, 0);
// ═══════════════════════════════════════════════════════════════
// 三元运算符的类型统一陷阱
// ═══════════════════════════════════════════════════════════════
Integer a = null;
Integer b = 10;
// 三元表达式要求两边类型一致
// 如果一边是基本类型，另一边会拆箱
Integer result = (a != null) ? a : 0; // OK
// Integer result2 = true ? null : 0; // NPE! null 被拆箱
}
}
7.4 包装类缓存机制
<mxfile>
<diagram id="wrapper-cache-mechanism" name="包装类缓存机制">
<mxGraphModel dx="1068" dy="484" grid="1" gridSize="10" guides="1" tooltips="1" connect="1" arrows="1" fold="1" page="1" pageScale="1" pageWidth="900" pageHeight="750" math="0" shadow="0">
<root>
<mxCell id="0" />
<mxCell id="1" parent="0" />
<mxCell id="2" parent="1" style="text;html=1;strokeColor=none;fillColor=none;align=center;verticalAlign=middle;fontSize=28;fontStyle=1;fontColor=#1E293B;" value="包装类缓存机制" vertex="1">
<mxGeometry height="45" width="400" x="250" y="20" as="geometry" />
</mxCell>
<mxCell id="3" parent="1" style="text;html=1;strokeColor=none;fillColor=#3B82F6;align=center;verticalAlign=middle;fontSize=13;fontColor=#FFFFFF;rounded=1;" value="JVM 对部分包装类实现了缓存，以节省内存和提高性能" vertex="1">
<mxGeometry height="30" width="500" x="200" y="65" as="geometry" />
</mxCell>
<mxCell id="4" parent="1" style="rounded=1;whiteSpace=wrap;html=1;fillColor=#F8FAFC;strokeColor=#E2E8F0;strokeWidth=2;" value="" vertex="1">
<mxGeometry height="380" width="820" x="40" y="115" as="geometry" />
</mxCell>
<mxCell id="5" parent="1" style="rounded=0;whiteSpace=wrap;html=1;fillColor=#1E293B;strokeColor=#0F172A;strokeWidth=1;fontSize=14;fontStyle=1;fontColor=#FFFFFF;" value="包装类" vertex="1">
<mxGeometry height="40" width="140" x="60" y="135" as="geometry" />
</mxCell>
<mxCell id="6" parent="1" style="rounded=0;whiteSpace=wrap;html=1;fillColor=#1E293B;strokeColor=#0F172A;strokeWidth=1;fontSize=14;fontStyle=1;fontColor=#FFFFFF;" value="缓存范围" vertex="1">
<mxGeometry height="40" width="160" x="200" y="135" as="geometry" />
</mxCell>
<mxCell id="7" parent="1" style="rounded=0;whiteSpace=wrap;html=1;fillColor=#1E293B;strokeColor=#0F172A;strokeWidth=1;fontSize=14;fontStyle=1;fontColor=#FFFFFF;" value="说明" vertex="1">
<mxGeometry height="40" width="280" x="360" y="135" as="geometry" />
</mxCell>
<mxCell id="8" parent="1" style="rounded=0;whiteSpace=wrap;html=1;fillColor=#1E293B;strokeColor=#0F172A;strokeWidth=1;fontSize=14;fontStyle=1;fontColor=#FFFFFF;" value="缓存状态" vertex="1">
<mxGeometry height="41" width="100" x="640" y="134" as="geometry" />
</mxCell>
<mxCell id="9" parent="1" style="rounded=0;whiteSpace=wrap;html=1;fillColor=#DBEAFE;strokeColor=#BFDBFE;strokeWidth=1;fontSize=14;fontStyle=1;fontColor=#1E40AF;fontFamily=Courier New;" value="Byte" vertex="1">
<mxGeometry height="38" width="140" x="60" y="175" as="geometry" />
</mxCell>
<mxCell id="10" parent="1" style="rounded=0;whiteSpace=wrap;html=1;fillColor=#EFF6FF;strokeColor=#BFDBFE;strokeWidth=1;fontSize=13;fontStyle=1;fontColor=#1E40AF;fontFamily=Courier New;" value="-128 ~ 127" vertex="1">
<mxGeometry height="38" width="160" x="200" y="175" as="geometry" />
</mxCell>
<mxCell id="11" parent="1" style="rounded=0;whiteSpace=wrap;html=1;fillColor=#EFF6FF;strokeColor=#BFDBFE;strokeWidth=1;fontSize=12;fontColor=#1E40AF;" value="全部缓存（byte 整个范围）" vertex="1">
<mxGeometry height="38" width="280" x="360" y="175" as="geometry" />
</mxCell>
<mxCell id="12" parent="1" style="rounded=1;whiteSpace=wrap;html=1;fillColor=#22C55E;strokeColor=#16A34A;strokeWidth=1;fontSize=11;fontStyle=1;fontColor=#FFFFFF;" value="✓ 全缓存" vertex="1">
<mxGeometry height="24" width="80" x="650" y="182" as="geometry" />
</mxCell>
<mxCell id="13" parent="1" style="rounded=0;whiteSpace=wrap;html=1;fillColor=#DBEAFE;strokeColor=#BFDBFE;strokeWidth=1;fontSize=14;fontStyle=1;fontColor=#1E40AF;fontFamily=Courier New;" value="Short" vertex="1">
<mxGeometry height="38" width="140" x="60" y="213" as="geometry" />
</mxCell>
<mxCell id="14" parent="1" style="rounded=0;whiteSpace=wrap;html=1;fillColor=#EFF6FF;strokeColor=#BFDBFE;strokeWidth=1;fontSize=13;fontStyle=1;fontColor=#1E40AF;fontFamily=Courier New;" value="-128 ~ 127" vertex="1">
<mxGeometry height="38" width="160" x="200" y="213" as="geometry" />
</mxCell>
<mxCell id="15" parent="1" style="rounded=0;whiteSpace=wrap;html=1;fillColor=#EFF6FF;strokeColor=#BFDBFE;strokeWidth=1;fontSize=12;fontColor=#1E40AF;" value="部分缓存" vertex="1">
<mxGeometry height="38" width="280" x="360" y="213" as="geometry" />
</mxCell>
<mxCell id="16" parent="1" style="rounded=1;whiteSpace=wrap;html=1;fillColor=#3B82F6;strokeColor=#2563EB;strokeWidth=1;fontSize=11;fontStyle=1;fontColor=#FFFFFF;" value="◐ 部分" vertex="1">
<mxGeometry height="24" width="80" x="650" y="220" as="geometry" />
</mxCell>
<mxCell id="17" parent="1" style="rounded=0;whiteSpace=wrap;html=1;fillColor=#FEF3C7;strokeColor=#FDE68A;strokeWidth=1;fontSize=14;fontStyle=1;fontColor=#92400E;fontFamily=Courier New;" value="Integer" vertex="1">
<mxGeometry height="38" width="140" x="60" y="251" as="geometry" />
</mxCell>
<mxCell id="18" parent="1" style="rounded=0;whiteSpace=wrap;html=1;fillColor=#FFFBEB;strokeColor=#FDE68A;strokeWidth=1;fontSize=13;fontStyle=1;fontColor=#92400E;fontFamily=Courier New;" value="-128 ~ 127" vertex="1">
<mxGeometry height="38" width="160" x="200" y="251" as="geometry" />
</mxCell>
<mxCell id="19" parent="1" style="rounded=0;whiteSpace=wrap;html=1;fillColor=#FFFBEB;strokeColor=#FDE68A;strokeWidth=1;fontSize=12;fontStyle=1;fontColor=#92400E;" value="可通过 JVM 参数扩展上限 ⭐" vertex="1">
<mxGeometry height="38" width="280" x="360" y="251" as="geometry" />
</mxCell>
<mxCell id="20" parent="1" style="rounded=1;whiteSpace=wrap;html=1;fillColor=#F59E0B;strokeColor=#D97706;strokeWidth=1;fontSize=11;fontStyle=1;fontColor=#FFFFFF;" value="◐ 可扩展" vertex="1">
<mxGeometry height="24" width="80" x="650" y="258" as="geometry" />
</mxCell>
<mxCell id="21" parent="1" style="rounded=0;whiteSpace=wrap;html=1;fillColor=#DBEAFE;strokeColor=#BFDBFE;strokeWidth=1;fontSize=14;fontStyle=1;fontColor=#1E40AF;fontFamily=Courier New;" value="Long" vertex="1">
<mxGeometry height="38" width="140" x="60" y="289" as="geometry" />
</mxCell>
<mxCell id="22" parent="1" style="rounded=0;whiteSpace=wrap;html=1;fillColor=#EFF6FF;strokeColor=#BFDBFE;strokeWidth=1;fontSize=13;fontStyle=1;fontColor=#1E40AF;fontFamily=Courier New;" value="-128 ~ 127" vertex="1">
<mxGeometry height="38" width="160" x="200" y="289" as="geometry" />
</mxCell>
<mxCell id="23" parent="1" style="rounded=0;whiteSpace=wrap;html=1;fillColor=#EFF6FF;strokeColor=#BFDBFE;strokeWidth=1;fontSize=12;fontColor=#1E40AF;" value="部分缓存" vertex="1">
<mxGeometry height="38" width="280" x="360" y="289" as="geometry" />
</mxCell>
<mxCell id="24" parent="1" style="rounded=1;whiteSpace=wrap;html=1;fillColor=#3B82F6;strokeColor=#2563EB;strokeWidth=1;fontSize=11;fontStyle=1;fontColor=#FFFFFF;" value="◐ 部分" vertex="1">
<mxGeometry height="24" width="80" x="650" y="296" as="geometry" />
</mxCell>
<mxCell id="25" parent="1" style="rounded=0;whiteSpace=wrap;html=1;fillColor=#DCFCE7;strokeColor=#BBF7D0;strokeWidth=1;fontSize=14;fontStyle=1;fontColor=#166534;fontFamily=Courier New;" value="Character" vertex="1">
<mxGeometry height="38" width="140" x="60" y="327" as="geometry" />
</mxCell>
<mxCell id="26" parent="1" style="rounded=0;whiteSpace=wrap;html=1;fillColor=#F0FDF4;strokeColor=#BBF7D0;strokeWidth=1;fontSize=13;fontStyle=1;fontColor=#166534;fontFamily=Courier New;" value="0 ~ 127" vertex="1">
<mxGeometry height="38" width="160" x="200" y="327" as="geometry" />
</mxCell>
<mxCell id="27" parent="1" style="rounded=0;whiteSpace=wrap;html=1;fillColor=#F0FDF4;strokeColor=#BBF7D0;strokeWidth=1;fontSize=12;fontColor=#166534;" value="ASCII 字符范围" vertex="1">
<mxGeometry height="38" width="280" x="360" y="327" as="geometry" />
</mxCell>
<mxCell id="28" parent="1" style="rounded=1;whiteSpace=wrap;html=1;fillColor=#22C55E;strokeColor=#16A34A;strokeWidth=1;fontSize=11;fontStyle=1;fontColor=#FFFFFF;" value="◐ 部分" vertex="1">
<mxGeometry height="24" width="80" x="650" y="334" as="geometry" />
</mxCell>
<mxCell id="29" parent="1" style="rounded=0;whiteSpace=wrap;html=1;fillColor=#F3E8FF;strokeColor=#E9D5FF;strokeWidth=1;fontSize=14;fontStyle=1;fontColor=#6D28D9;fontFamily=Courier New;" value="Boolean" vertex="1">
<mxGeometry height="38" width="140" x="60" y="365" as="geometry" />
</mxCell>
<mxCell id="30" parent="1" style="rounded=0;whiteSpace=wrap;html=1;fillColor=#FAF5FF;strokeColor=#E9D5FF;strokeWidth=1;fontSize=13;fontStyle=1;fontColor=#6D28D9;fontFamily=Courier New;" value="true / false" vertex="1">
<mxGeometry height="38" width="160" x="200" y="365" as="geometry" />
</mxCell>
<mxCell id="31" parent="1" style="rounded=0;whiteSpace=wrap;html=1;fillColor=#FAF5FF;strokeColor=#E9D5FF;strokeWidth=1;fontSize=12;fontColor=#6D28D9;" value="仅两个实例（单例模式）" vertex="1">
<mxGeometry height="38" width="280" x="360" y="365" as="geometry" />
</mxCell>
<mxCell id="32" parent="1" style="rounded=1;whiteSpace=wrap;html=1;fillColor=#8B5CF6;strokeColor=#7C3AED;strokeWidth=1;fontSize=11;fontStyle=1;fontColor=#FFFFFF;" value="✓ 全缓存" vertex="1">
<mxGeometry height="24" width="80" x="650" y="372" as="geometry" />
</mxCell>
<mxCell id="33" parent="1" style="rounded=0;whiteSpace=wrap;html=1;fillColor=#FEE2E2;strokeColor=#FECACA;strokeWidth=1;fontSize=14;fontStyle=1;fontColor=#991B1B;fontFamily=Courier New;" value="Float" vertex="1">
<mxGeometry height="38" width="140" x="60" y="403" as="geometry" />
</mxCell>
<mxCell id="34" parent="1" style="rounded=0;whiteSpace=wrap;html=1;fillColor=#FEF2F2;strokeColor=#FECACA;strokeWidth=1;fontSize=13;fontStyle=1;fontColor=#991B1B;" value="无缓存" vertex="1">
<mxGeometry height="38" width="160" x="200" y="403" as="geometry" />
</mxCell>
<mxCell id="35" parent="1" style="rounded=0;whiteSpace=wrap;html=1;fillColor=#FEF2F2;strokeColor=#FECACA;strokeWidth=1;fontSize=12;fontColor=#991B1B;" value="浮点数范围太大，无法有效缓存" vertex="1">
<mxGeometry height="38" width="280" x="360" y="403" as="geometry" />
</mxCell>
<mxCell id="36" parent="1" style="rounded=1;whiteSpace=wrap;html=1;fillColor=#EF4444;strokeColor=#DC2626;strokeWidth=1;fontSize=11;fontStyle=1;fontColor=#FFFFFF;" value="✗ 无" vertex="1">
<mxGeometry height="24" width="80" x="650" y="410" as="geometry" />
</mxCell>
<mxCell id="37" parent="1" style="rounded=0;whiteSpace=wrap;html=1;fillColor=#FEE2E2;strokeColor=#FECACA;strokeWidth=1;fontSize=14;fontStyle=1;fontColor=#991B1B;fontFamily=Courier New;" value="Double" vertex="1">
<mxGeometry height="38" width="140" x="60" y="441" as="geometry" />
</mxCell>
<mxCell id="38" parent="1" style="rounded=0;whiteSpace=wrap;html=1;fillColor=#FEF2F2;strokeColor=#FECACA;strokeWidth=1;fontSize=13;fontStyle=1;fontColor=#991B1B;" value="无缓存" vertex="1">
<mxGeometry height="38" width="160" x="200" y="441" as="geometry" />
</mxCell>
<mxCell id="39" parent="1" style="rounded=0;whiteSpace=wrap;html=1;fillColor=#FEF2F2;strokeColor=#FECACA;strokeWidth=1;fontSize=12;fontColor=#991B1B;" value="浮点数范围太大，无法有效缓存" vertex="1">
<mxGeometry height="38" width="280" x="360" y="441" as="geometry" />
</mxCell>
<mxCell id="40" parent="1" style="rounded=1;whiteSpace=wrap;html=1;fillColor=#EF4444;strokeColor=#DC2626;strokeWidth=1;fontSize=11;fontStyle=1;fontColor=#FFFFFF;" value="✗ 无" vertex="1">
<mxGeometry height="24" width="80" x="650" y="448" as="geometry" />
</mxCell>
<mxCell id="41" parent="1" style="rounded=1;whiteSpace=wrap;html=1;fillColor=#FFFBEB;strokeColor=#F59E0B;strokeWidth=2;" value="" vertex="1">
<mxGeometry height="180" width="85" x="755" y="215" as="geometry" />
</mxCell>
<mxCell id="42" parent="1" style="text;html=1;strokeColor=none;fillColor=#F59E0B;align=center;verticalAlign=middle;fontSize=11;fontStyle=1;fontColor=#FFFFFF;rounded=1;" value="💡 提示" vertex="1">
<mxGeometry height="22" width="60" x="765" y="225" as="geometry" />
</mxCell>
<mxCell id="43" parent="1" style="text;html=1;strokeColor=none;fillColor=none;align=center;verticalAlign=middle;fontSize=10;fontColor=#92400E;" value="Integer 缓存<br>上限可配置" vertex="1">
<mxGeometry height="35" width="75" x="760" y="255" as="geometry" />
</mxCell>
<mxCell id="44" parent="1" style="text;html=1;strokeColor=none;fillColor=#FEF3C7;align=center;verticalAlign=middle;fontSize=9;fontFamily=Courier New;fontColor=#92400E;rounded=1;" value="-XX:AutoBox<br>CacheMax" vertex="1">
<mxGeometry height="35" width="75" x="760" y="295" as="geometry" />
</mxCell>
<mxCell id="45" parent="1" style="text;html=1;strokeColor=none;fillColor=none;align=center;verticalAlign=middle;fontSize=10;fontColor=#92400E;" value="例如设为<br>1000" vertex="1">
<mxGeometry height="30" width="75" x="760" y="335" as="geometry" />
</mxCell>
<mxCell id="46" parent="1" style="text;html=1;strokeColor=none;fillColor=#F59E0B;align=center;verticalAlign=middle;fontSize=9;fontStyle=1;fontColor=#FFFFFF;rounded=1;" value="缓存 -128~1000" vertex="1">
<mxGeometry height="20" width="80" x="757" y="368" as="geometry" />
</mxCell>
<mxCell id="47" parent="1" style="text;html=1;strokeColor=none;fillColor=#FEE2E2;align=center;verticalAlign=middle;fontSize=12;fontStyle=1;fontColor=#991B1B;rounded=1;" value="⚠️ 注意：缓存范围内的值使用 == 比较返回 true，范围外返回 false，建议始终使用 equals() 比较包装类" vertex="1">
<mxGeometry height="32" width="700" x="100" y="510" as="geometry" />
</mxCell>
<mxCell id="48" parent="1" style="rounded=1;whiteSpace=wrap;html=1;fillColor=#F0FDF4;strokeColor=#22C55E;strokeWidth=2;" value="" vertex="1">
<mxGeometry height="170" width="820" x="40" y="560" as="geometry" />
</mxCell>
<mxCell id="49" parent="1" style="text;html=1;strokeColor=none;fillColor=#22C55E;align=center;verticalAlign=middle;fontSize=13;fontStyle=1;fontColor=#FFFFFF;rounded=1;" value="📝 代码示例" vertex="1">
<mxGeometry height="26" width="100" x="60" y="575" as="geometry" />
</mxCell>
<mxCell id="50" parent="1" style="text;html=1;strokeColor=none;fillColor=#DCFCE7;align=left;verticalAlign=middle;fontSize=12;fontFamily=Courier New;fontColor=#166534;rounded=1;spacingLeft=10;" value="Integer a = 127;<br>Integer b = 127;<br>System.out.println(a == b);" vertex="1">
<mxGeometry height="55" width="220" x="60" y="615" as="geometry" />
</mxCell>
<mxCell id="51" parent="1" style="text;html=1;strokeColor=none;fillColor=#22C55E;align=center;verticalAlign=middle;fontSize=11;fontStyle=1;fontColor=#FFFFFF;rounded=1;" value="// true（缓存范围内）" vertex="1">
<mxGeometry height="24" width="160" x="60" y="680" as="geometry" />
</mxCell>
<mxCell id="52" parent="1" style="text;html=1;strokeColor=none;fillColor=#FEE2E2;align=left;verticalAlign=middle;fontSize=12;fontFamily=Courier New;fontColor=#991B1B;rounded=1;spacingLeft=10;" value="Integer c = 128;<br>Integer d = 128;<br>System.out.println(c == d);" vertex="1">
<mxGeometry height="55" width="220" x="310" y="615" as="geometry" />
</mxCell>
<mxCell id="53" parent="1" style="text;html=1;strokeColor=none;fillColor=#EF4444;align=center;verticalAlign=middle;fontSize=11;fontStyle=1;fontColor=#FFFFFF;rounded=1;" value="// false（超出缓存范围）" vertex="1">
<mxGeometry height="24" width="175" x="310" y="680" as="geometry" />
</mxCell>
<mxCell id="54" parent="1" style="text;html=1;strokeColor=none;fillColor=#DBEAFE;align=left;verticalAlign=middle;fontSize=12;fontFamily=Courier New;fontColor=#1E40AF;rounded=1;spacingLeft=10;" value="Integer e = 128;<br>Integer f = 128;<br>System.out.println(e.equals(f));" vertex="1">
<mxGeometry height="55" width="280" x="560" y="615" as="geometry" />
</mxCell>
<mxCell id="55" parent="1" style="text;html=1;strokeColor=none;fillColor=#3B82F6;align=center;verticalAlign=middle;fontSize=11;fontStyle=1;fontColor=#FFFFFF;rounded=1;" value="// true（推荐写法 ✓）" vertex="1">
<mxGeometry height="24" width="145" x="560" y="680" as="geometry" />
</mxCell>
</root>
</mxGraphModel>
</diagram>
</mxfile>
Integer 缓存源码分析：
// Integer.java 源码（JDK 8+）
public final class Integer extends Number implements Comparable<Integer> {
// valueOf 方法使用缓存
public static Integer valueOf(int i) {
// 如果在缓存范围内，直接返回缓存的对象
if (i >= IntegerCache.low && i <= IntegerCache.high)
return IntegerCache.cache[i + (-IntegerCache.low)];
// 否则创建新对象
return new Integer(i);
}
// 内部缓存类
private static class IntegerCache {
static final int low = -128; // 最小值固定
static final int high; // 最大值可配置
static final Integer[] cache; // 缓存数组
static {
// 默认最大值 127，可通过 JVM 参数调整
int h = 127;
String integerCacheHighPropValue =
VM.getSavedProperty("java.lang.Integer.IntegerCache.high");
if (integerCacheHighPropValue != null) {
int i = parseInt(integerCacheHighPropValue);
i = Math.max(i, 127); // 至少 127
h = Math.min(i, Integer.MAX_VALUE - (-low) - 1);
}
high = h;
// 创建缓存数组
cache = new Integer[(high - low) + 1];
int j = low;
for (int k = 0; k < cache.length; k++)
cache[k] = new Integer(j++);
}
}
}
<mxfile>
<diagram id="integer-cache" name="Integer 缓存机制图解">
<mxGraphModel dx="926" dy="817" grid="1" gridSize="10" guides="1" tooltips="1" connect="1" arrows="1" fold="1" page="1" pageScale="1" pageWidth="900" pageHeight="750" math="0" shadow="0">
<root>
<mxCell id="0" />
<mxCell id="1" parent="0" />
<mxCell id="2" parent="1" style="rounded=1;whiteSpace=wrap;html=1;fillColor=#fafafa;strokeColor=#5c6bc0;strokeWidth=3;shadow=1;" value="" vertex="1">
<mxGeometry height="720" width="820" x="40" y="20" as="geometry" />
</mxCell>
<mxCell id="3" parent="1" style="text;html=1;strokeColor=none;fillColor=none;align=center;verticalAlign=middle;whiteSpace=wrap;rounded=0;fontSize=26;fontStyle=1;fontColor=#1a237e;" value="Integer 缓存机制图解" vertex="1">
<mxGeometry height="45" width="400" x="250" y="35" as="geometry" />
</mxCell>
<mxCell id="4" parent="1" style="text;html=1;strokeColor=none;fillColor=none;align=center;verticalAlign=middle;whiteSpace=wrap;rounded=0;fontSize=15;fontColor=#5c6bc0;" value="Integer.valueOf(100) 的执行过程" vertex="1">
<mxGeometry height="25" width="340" x="280" y="75" as="geometry" />
</mxCell>
<mxCell id="5" parent="1" style="rounded=1;whiteSpace=wrap;html=1;fillColor=#e8eaf6;strokeColor=#3f51b5;strokeWidth=2;dashed=1;" value="" vertex="1">
<mxGeometry height="160" width="780" x="60" y="115" as="geometry" />
</mxCell>
<mxCell id="6" parent="1" style="text;html=1;strokeColor=none;fillColor=none;align=center;verticalAlign=middle;whiteSpace=wrap;rounded=0;fontSize=14;fontStyle=1;fontColor=#3f51b5;" value="IntegerCache.cache (静态数组，JVM启动时初始化)" vertex="1">
<mxGeometry height="30" width="780" x="60" y="120" as="geometry" />
</mxCell>
<mxCell id="7" parent="1" style="rounded=0;whiteSpace=wrap;html=1;fillColor=#c5cae9;strokeColor=#3f51b5;strokeWidth=2;" value="" vertex="1">
<mxGeometry height="50" width="70" x="80" y="160" as="geometry" />
</mxCell>
<mxCell id="8" parent="1" style="text;html=1;strokeColor=none;fillColor=none;align=center;verticalAlign=middle;whiteSpace=wrap;rounded=0;fontSize=13;" value="<b>-128</b><br><font color="#757575" style="font-size: 11px;">[0]</font>" vertex="1">
<mxGeometry height="50" width="70" x="80" y="160" as="geometry" />
</mxCell>
<mxCell id="9" parent="1" style="rounded=0;whiteSpace=wrap;html=1;fillColor=#c5cae9;strokeColor=#3f51b5;strokeWidth=2;" value="" vertex="1">
<mxGeometry height="50" width="70" x="150" y="160" as="geometry" />
</mxCell>
<mxCell id="10" parent="1" style="text;html=1;strokeColor=none;fillColor=none;align=center;verticalAlign=middle;whiteSpace=wrap;rounded=0;fontSize=13;" value="<b>-127</b><br><font color="#757575" style="font-size: 11px;">[1]</font>" vertex="1">
<mxGeometry height="50" width="70" x="150" y="160" as="geometry" />
</mxCell>
<mxCell id="11" parent="1" style="rounded=0;whiteSpace=wrap;html=1;fillColor=#e8eaf6;strokeColor=#9fa8da;strokeWidth=1;strokeDasharray=3 3;" value="" vertex="1">
<mxGeometry height="50" width="60" x="220" y="160" as="geometry" />
</mxCell>
<mxCell id="12" parent="1" style="text;html=1;strokeColor=none;fillColor=none;align=center;verticalAlign=middle;whiteSpace=wrap;rounded=0;fontSize=16;" value="<font color="#9e9e9e">...</font>" vertex="1">
<mxGeometry height="50" width="60" x="220" y="160" as="geometry" />
</mxCell>
<mxCell id="13" parent="1" style="rounded=0;whiteSpace=wrap;html=1;fillColor=#c5cae9;strokeColor=#3f51b5;strokeWidth=2;" value="" vertex="1">
<mxGeometry height="50" width="70" x="280" y="160" as="geometry" />
</mxCell>
<mxCell id="14" parent="1" style="text;html=1;strokeColor=none;fillColor=none;align=center;verticalAlign=middle;whiteSpace=wrap;rounded=0;fontSize=13;" value="<b>0</b><br><font color="#757575" style="font-size: 11px;">[128]</font>" vertex="1">
<mxGeometry height="50" width="70" x="280" y="160" as="geometry" />
</mxCell>
<mxCell id="15" parent="1" style="rounded=0;whiteSpace=wrap;html=1;fillColor=#e8eaf6;strokeColor=#9fa8da;strokeWidth=1;strokeDasharray=3 3;" value="" vertex="1">
<mxGeometry height="50" width="60" x="350" y="160" as="geometry" />
</mxCell>
<mxCell id="16" parent="1" style="text;html=1;strokeColor=none;fillColor=none;align=center;verticalAlign=middle;whiteSpace=wrap;rounded=0;fontSize=16;" value="<font color="#9e9e9e">...</font>" vertex="1">
<mxGeometry height="50" width="60" x="350" y="160" as="geometry" />
</mxCell>
<mxCell id="17" parent="1" style="rounded=0;whiteSpace=wrap;html=1;fillColor=#4caf50;strokeColor=#2e7d32;strokeWidth=3;" value="" vertex="1">
<mxGeometry height="50" width="80" x="410" y="160" as="geometry" />
</mxCell>
<mxCell id="18" parent="1" style="text;html=1;strokeColor=none;fillColor=none;align=center;verticalAlign=middle;whiteSpace=wrap;rounded=0;fontSize=14;" value="<font color="#ffffff"><b>100</b><br><span style="font-size: 11px;">[228]</span></font>" vertex="1">
<mxGeometry height="50" width="80" x="410" y="160" as="geometry" />
</mxCell>
<mxCell id="19" parent="1" style="rounded=0;whiteSpace=wrap;html=1;fillColor=#e8eaf6;strokeColor=#9fa8da;strokeWidth=1;strokeDasharray=3 3;" value="" vertex="1">
<mxGeometry height="50" width="60" x="490" y="160" as="geometry" />
</mxCell>
<mxCell id="20" parent="1" style="text;html=1;strokeColor=none;fillColor=none;align=center;verticalAlign=middle;whiteSpace=wrap;rounded=0;fontSize=16;" value="<font color="#9e9e9e">...</font>" vertex="1">
<mxGeometry height="50" width="60" x="490" y="160" as="geometry" />
</mxCell>
<mxCell id="21" parent="1" style="rounded=0;whiteSpace=wrap;html=1;fillColor=#c5cae9;strokeColor=#3f51b5;strokeWidth=2;" value="" vertex="1">
<mxGeometry height="50" width="70" x="550" y="160" as="geometry" />
</mxCell>
<mxCell id="22" parent="1" style="text;html=1;strokeColor=none;fillColor=none;align=center;verticalAlign=middle;whiteSpace=wrap;rounded=0;fontSize=13;" value="<b>127</b><br><font color="#757575" style="font-size: 11px;">[255]</font>" vertex="1">
<mxGeometry height="50" width="70" x="550" y="160" as="geometry" />
</mxCell>
<mxCell id="23" parent="1" style="rounded=1;whiteSpace=wrap;html=1;fillColor=#fff3e0;strokeColor=#ff9800;strokeWidth=1;" value="" vertex="1">
<mxGeometry height="60" width="180" x="640" y="155" as="geometry" />
</mxCell>
<mxCell id="24" parent="1" style="text;html=1;strokeColor=none;fillColor=none;align=center;verticalAlign=middle;whiteSpace=wrap;rounded=0;fontSize=13;" value="📌 缓存范围<br><b>-128 ~ 127</b><br><font style="font-size: 11px;" color="#757575">共 256 个对象</font>" vertex="1">
<mxGeometry height="60" width="180" x="640" y="155" as="geometry" />
</mxCell>
<mxCell id="25" parent="1" style="text;html=1;strokeColor=none;fillColor=none;align=center;verticalAlign=middle;whiteSpace=wrap;rounded=0;fontSize=12;fontColor=#5c6bc0;" value="<font face="Courier New">index = value + 128</font>" vertex="1">
<mxGeometry height="25" width="200" x="200" y="220" as="geometry" />
</mxCell>
<mxCell id="26" parent="1" style="rounded=1;whiteSpace=wrap;html=1;fillColor=#e8f5e9;strokeColor=#4caf50;strokeWidth=2;" value="" vertex="1">
<mxGeometry height="175" width="780" x="60" y="290" as="geometry" />
</mxCell>
<mxCell id="27" parent="1" style="text;html=1;strokeColor=none;fillColor=none;align=left;verticalAlign=middle;whiteSpace=wrap;rounded=0;fontSize=15;fontStyle=1;fontColor=#2e7d32;spacingLeft=10;" value="✅ 缓存命中 (值在 -128 ~ 127 范围内)" vertex="1">
<mxGeometry height="30" width="400" x="60" y="295" as="geometry" />
</mxCell>
<mxCell id="28" parent="1" style="rounded=1;whiteSpace=wrap;html=1;fillColor=#81c784;strokeColor=#4caf50;strokeWidth=2;" value="" vertex="1">
<mxGeometry height="45" width="180" x="90" y="335" as="geometry" />
</mxCell>
<mxCell id="29" parent="1" style="text;html=1;strokeColor=none;fillColor=none;align=center;verticalAlign=middle;whiteSpace=wrap;rounded=0;fontSize=14;fontColor=#1b5e20;" value="<font face="Courier New">Integer a = 100;</font>" vertex="1">
<mxGeometry height="45" width="180" x="90" y="335" as="geometry" />
</mxCell>
<mxCell id="30" edge="1" parent="1" style="endArrow=classic;html=1;strokeColor=#4caf50;strokeWidth=2;entryX=0;entryY=0.5;entryDx=0;entryDy=0;flowAnimation=1;" value="">
<mxGeometry height="50" relative="1" width="50" as="geometry">
<mxPoint x="270" y="357" as="sourcePoint" />
<mxPoint x="410" y="357" as="targetPoint" />
</mxGeometry>
</mxCell>
<mxCell id="31" parent="1" style="rounded=1;whiteSpace=wrap;html=1;fillColor=#81c784;strokeColor=#4caf50;strokeWidth=2;" value="" vertex="1">
<mxGeometry height="45" width="180" x="90" y="390" as="geometry" />
</mxCell>
<mxCell id="32" parent="1" style="text;html=1;strokeColor=none;fillColor=none;align=center;verticalAlign=middle;whiteSpace=wrap;rounded=0;fontSize=14;fontColor=#1b5e20;" value="<font face="Courier New">Integer b = 100;</font>" vertex="1">
<mxGeometry height="45" width="180" x="90" y="390" as="geometry" />
</mxCell>
<mxCell id="33" edge="1" parent="1" style="endArrow=classic;html=1;strokeColor=#4caf50;strokeWidth=2;flowAnimation=1;" value="">
<mxGeometry height="50" relative="1" width="50" as="geometry">
<mxPoint x="270" y="412" as="sourcePoint" />
<mxPoint x="410" y="380" as="targetPoint" />
</mxGeometry>
</mxCell>
<mxCell id="34" parent="1" style="rounded=1;whiteSpace=wrap;html=1;fillColor=#4caf50;strokeColor=#2e7d32;strokeWidth=3;shadow=1;" value="" vertex="1">
<mxGeometry height="70" width="140" x="410" y="340" as="geometry" />
</mxCell>
<mxCell id="35" parent="1" style="text;html=1;strokeColor=none;fillColor=none;align=center;verticalAlign=middle;whiteSpace=wrap;rounded=0;fontSize=14;" value="<font color="#ffffff"><b>cache[228]</b><br>Integer(100)<br><font style="font-size: 11px;">@0x1234</font></font>" vertex="1">
<mxGeometry height="70" width="140" x="410" y="340" as="geometry" />
</mxCell>
<mxCell id="36" parent="1" style="text;html=1;strokeColor=none;fillColor=none;align=center;verticalAlign=middle;whiteSpace=wrap;rounded=0;fontSize=12;fontColor=#2e7d32;" value="返回同一个<br>缓存对象" vertex="1">
<mxGeometry height="40" width="80" x="310" y="355" as="geometry" />
</mxCell>
<mxCell id="37" parent="1" style="rounded=1;whiteSpace=wrap;html=1;fillColor=#c8e6c9;strokeColor=#4caf50;strokeWidth=2;" value="" vertex="1">
<mxGeometry height="50" width="230" x="590" y="350" as="geometry" />
</mxCell>
<mxCell id="38" parent="1" style="text;html=1;strokeColor=none;fillColor=none;align=center;verticalAlign=middle;whiteSpace=wrap;rounded=0;fontSize=14;" value="<font face="Courier New">a == b</font> → <font color="#2e7d32"><b>true</b></font><br><font color="#757575" style="font-size: 12px;">(同一个对象，地址相同)</font>" vertex="1">
<mxGeometry height="50" width="230" x="590" y="350" as="geometry" />
</mxCell>
<mxCell id="39" edge="1" parent="1" style="endArrow=none;html=1;strokeColor=#bdbdbd;strokeWidth=2;dashed=1;" value="">
<mxGeometry height="50" relative="1" width="50" as="geometry">
<mxPoint x="80" y="485" as="sourcePoint" />
<mxPoint x="820" y="485" as="targetPoint" />
</mxGeometry>
</mxCell>
<mxCell id="40" parent="1" style="rounded=1;whiteSpace=wrap;html=1;fillColor=#ffebee;strokeColor=#e53935;strokeWidth=2;" value="" vertex="1">
<mxGeometry height="200" width="780" x="60" y="505" as="geometry" />
</mxCell>
<mxCell id="41" parent="1" style="text;html=1;strokeColor=none;fillColor=none;align=left;verticalAlign=middle;whiteSpace=wrap;rounded=0;fontSize=15;fontStyle=1;fontColor=#c62828;spacingLeft=10;" value="❌ 缓存未命中 (值超出 -128 ~ 127 范围)" vertex="1">
<mxGeometry height="30" width="400" x="60" y="510" as="geometry" />
</mxCell>
<mxCell id="42" parent="1" style="rounded=1;whiteSpace=wrap;html=1;fillColor=#ef9a9a;strokeColor=#e53935;strokeWidth=2;" value="" vertex="1">
<mxGeometry height="45" width="180" x="90" y="555" as="geometry" />
</mxCell>
<mxCell id="43" parent="1" style="text;html=1;strokeColor=none;fillColor=none;align=center;verticalAlign=middle;whiteSpace=wrap;rounded=0;fontSize=14;fontColor=#b71c1c;" value="<font face="Courier New">Integer c = 200;</font>" vertex="1">
<mxGeometry height="45" width="180" x="90" y="555" as="geometry" />
</mxCell>
<mxCell id="44" edge="1" parent="1" style="endArrow=classic;html=1;strokeColor=#e53935;strokeWidth=2;flowAnimation=1;" value="">
<mxGeometry height="50" relative="1" width="50" as="geometry">
<mxPoint x="270" y="577" as="sourcePoint" />
<mxPoint x="390" y="577" as="targetPoint" />
</mxGeometry>
</mxCell>
<mxCell id="45" parent="1" style="text;html=1;strokeColor=none;fillColor=none;align=center;verticalAlign=middle;whiteSpace=wrap;rounded=0;fontSize=11;fontColor=#e53935;fontStyle=1;" value="new" vertex="1">
<mxGeometry height="20" width="40" x="310" y="555" as="geometry" />
</mxCell>
<mxCell id="46" parent="1" style="rounded=1;whiteSpace=wrap;html=1;fillColor=#e53935;strokeColor=#b71c1c;strokeWidth=2;shadow=1;" value="" vertex="1">
<mxGeometry height="55" width="130" x="390" y="550" as="geometry" />
</mxCell>
<mxCell id="47" parent="1" style="text;html=1;strokeColor=none;fillColor=none;align=center;verticalAlign=middle;whiteSpace=wrap;rounded=0;fontSize=13;" value="<font color="#ffffff"><b>Integer(200)</b><br><font style="font-size: 11px;">@0x5678</font></font>" vertex="1">
<mxGeometry height="55" width="130" x="390" y="550" as="geometry" />
</mxCell>
<mxCell id="48" parent="1" style="rounded=1;whiteSpace=wrap;html=1;fillColor=#ef9a9a;strokeColor=#e53935;strokeWidth=2;" value="" vertex="1">
<mxGeometry height="45" width="180" x="90" y="615" as="geometry" />
</mxCell>
<mxCell id="49" parent="1" style="text;html=1;strokeColor=none;fillColor=none;align=center;verticalAlign=middle;whiteSpace=wrap;rounded=0;fontSize=14;fontColor=#b71c1c;" value="<font face="Courier New">Integer d = 200;</font>" vertex="1">
<mxGeometry height="45" width="180" x="90" y="615" as="geometry" />
</mxCell>
<mxCell id="50" edge="1" parent="1" style="endArrow=classic;html=1;strokeColor=#e53935;strokeWidth=2;flowAnimation=1;" value="">
<mxGeometry height="50" relative="1" width="50" as="geometry">
<mxPoint x="270" y="637" as="sourcePoint" />
<mxPoint x="390" y="637" as="targetPoint" />
</mxGeometry>
</mxCell>
<mxCell id="51" parent="1" style="text;html=1;strokeColor=none;fillColor=none;align=center;verticalAlign=middle;whiteSpace=wrap;rounded=0;fontSize=11;fontColor=#e53935;fontStyle=1;" value="new" vertex="1">
<mxGeometry height="20" width="40" x="310" y="615" as="geometry" />
</mxCell>
<mxCell id="52" parent="1" style="rounded=1;whiteSpace=wrap;html=1;fillColor=#e53935;strokeColor=#b71c1c;strokeWidth=2;shadow=1;" value="" vertex="1">
<mxGeometry height="55" width="130" x="390" y="615" as="geometry" />
</mxCell>
<mxCell id="53" parent="1" style="text;html=1;strokeColor=none;fillColor=none;align=center;verticalAlign=middle;whiteSpace=wrap;rounded=0;fontSize=13;" value="<font color="#ffffff"><b>Integer(200)</b><br><font style="font-size: 11px;">@0x9ABC</font></font>" vertex="1">
<mxGeometry height="55" width="130" x="390" y="615" as="geometry" />
</mxCell>
<mxCell id="54" parent="1" style="text;html=1;strokeColor=none;fillColor=none;align=center;verticalAlign=middle;whiteSpace=wrap;rounded=0;fontSize=12;fontColor=#c62828;" value="每次都创建<br>新对象" vertex="1">
<mxGeometry height="40" width="70" x="520" y="595" as="geometry" />
</mxCell>
<mxCell id="55" parent="1" style="text;html=1;strokeColor=none;fillColor=none;align=center;verticalAlign=middle;whiteSpace=wrap;rounded=0;fontSize=28;fontStyle=1;fontColor=#e53935;" value="≠" vertex="1">
<mxGeometry height="30" width="30" x="440" y="600" as="geometry" />
</mxCell>
<mxCell id="56" parent="1" style="rounded=1;whiteSpace=wrap;html=1;fillColor=#ffcdd2;strokeColor=#e53935;strokeWidth=2;" value="" vertex="1">
<mxGeometry height="50" width="230" x="590" y="580" as="geometry" />
</mxCell>
<mxCell id="57" parent="1" style="text;html=1;strokeColor=none;fillColor=none;align=center;verticalAlign=middle;whiteSpace=wrap;rounded=0;fontSize=14;" value="<font face="Courier New">c == d</font> → <font color="#c62828"><b>false</b></font><br><font color="#757575" style="font-size: 12px;">(不同对象，地址不同)</font>" vertex="1">
<mxGeometry height="50" width="230" x="590" y="580" as="geometry" />
</mxCell>
<mxCell id="58" parent="1" style="rounded=1;whiteSpace=wrap;html=1;fillColor=#fff8e1;strokeColor=#ffa000;strokeWidth=2;" value="" vertex="1">
<mxGeometry height="30" width="780" x="50" y="750" as="geometry" />
</mxCell>
<mxCell id="59" parent="1" style="text;html=1;strokeColor=none;fillColor=none;align=center;verticalAlign=middle;whiteSpace=wrap;rounded=0;fontSize=13;fontColor=#e65100;fontStyle=1;" value="💡 最佳实践：比较包装类型的值时，始终使用 equals() 方法，避免 == 带来的陷阱" vertex="1">
<mxGeometry height="30" width="780" x="50" y="750" as="geometry" />
</mxCell>
</root>
</mxGraphModel>
</diagram>
</mxfile>
public class CacheDemo {
public static void main(String[] args) {
// ═══════════════════════════════════════════════════════════════
// 缓存范围内
// ═══════════════════════════════════════════════════════════════
Integer a = 127;
Integer b = 127;
System.out.println("a == b: " + (a == b)); // true
Integer c = -128;
Integer d = -128;
System.out.println("c == d: " + (c == d)); // true
// ═══════════════════════════════════════════════════════════════
// 超出缓存范围
// ═══════════════════════════════════════════════════════════════
Integer e = 128;
Integer f = 128;
System.out.println("e == f: " + (e == f)); // false
Integer g = -129;
Integer h = -129;
System.out.println("g == h: " + (g == h)); // false
// ═══════════════════════════════════════════════════════════════
// new 强制创建新对象（绕过缓存）
// ═══════════════════════════════════════════════════════════════
Integer i = new Integer(100); // 直接 new，不使用缓存
Integer j = Integer.valueOf(100); // 使用缓存
System.out.println("i == j: " + (i == j)); // false
// ⚠️ 从 JDK 9 开始，new Integer() 被标记为 @Deprecated
// 推荐使用 Integer.valueOf()
// ═══════════════════════════════════════════════════════════════
// Boolean 缓存
// ═══════════════════════════════════════════════════════════════
Boolean t1 = true;
Boolean t2 = Boolean.valueOf(true);
Boolean t3 = Boolean.TRUE;
System.out.println("t1 == t2: " + (t1 == t2)); // true
System.out.println("t1 == t3: " + (t1 == t3)); // true
}
}
// JVM 参数调整 Integer 缓存上限
// java -XX:AutoBoxCacheMax=1000 CacheDemo
7.5 装箱拆箱的性能影响
public class BoxingPerformanceDemo {
public static void main(String[] args) {
// ═══════════════════════════════════════════════════════════════
// 性能陷阱：频繁装箱拆箱
// ═══════════════════════════════════════════════════════════════
// ❌ 错误写法：Long 导致大量装箱
long startBad = System.currentTimeMillis();
Long sumBad = 0L; // 使用包装类型
for (long i = 0; i <= 1_000_000_000L; i++) {
sumBad += i; // 每次都要拆箱、相加、装箱
}
long endBad = System.currentTimeMillis();
System.out.println("包装类型耗时: " + (endBad - startBad) + "ms");
// ✅ 正确写法：使用基本类型
long startGood = System.currentTimeMillis();
long sumGood = 0L; // 使用基本类型
for (long i = 0; i <= 1_000_000_000L; i++) {
sumGood += i; // 纯基本类型运算
}
long endGood = System.currentTimeMillis();
System.out.println("基本类型耗时: " + (endGood - startGood) + "ms");
// 结果对比（示例）:
// 包装类型耗时: 约 6000ms
// 基本类型耗时: 约 600ms
// 性能差 10 倍！
}
}
<mxfile>
<diagram id="boxing-best-practices-fixed" name="装箱拆箱最佳实践">
<mxGraphModel dx="1068" dy="484" grid="1" gridSize="10" guides="1" tooltips="1" connect="1" arrows="1" fold="1" page="1" pageScale="1" pageWidth="900" pageHeight="850" math="0" shadow="0">
<root>
<mxCell id="0" />
<mxCell id="1" parent="0" />
<mxCell id="2" parent="1" style="text;html=1;strokeColor=none;fillColor=none;align=center;verticalAlign=middle;fontSize=26;fontStyle=1;fontColor=#1E293B;" value="Java 装箱拆箱 (Boxing/Unboxing) 最佳实践" vertex="1">
<mxGeometry height="45" width="500" x="200" y="20" as="geometry" />
</mxCell>
<mxCell id="3" parent="1" style="text;html=1;strokeColor=none;fillColor=#8B5CF6;align=center;verticalAlign=middle;fontSize=13;fontColor=#FFFFFF;rounded=1;" value="基本类型 (Primitive) vs 包装类型 (Wrapper) 避坑指南" vertex="1">
<mxGeometry height="28" width="320" x="300" y="65" as="geometry" />
</mxCell>
<mxCell id="4" parent="1" style="rounded=1;whiteSpace=wrap;html=1;fillColor=#F0FDF4;strokeColor=#22C55E;strokeWidth=2;arcSize=6;" value="" vertex="1">
<mxGeometry height="280" width="400" x="40" y="110" as="geometry" />
</mxCell>
<mxCell id="5" parent="1" style="text;html=1;strokeColor=none;fillColor=#22C55E;align=center;verticalAlign=middle;fontSize=15;fontStyle=1;fontColor=#FFFFFF;rounded=1;" value="✅ 推荐做法 (DO)" vertex="1">
<mxGeometry height="32" width="140" x="40" y="110" as="geometry" />
</mxCell>
<mxCell id="6" parent="1" style="rounded=1;whiteSpace=wrap;html=1;fillColor=#FFFFFF;strokeColor=#BBF7D0;strokeWidth=1;" value="" vertex="1">
<mxGeometry height="55" width="370" x="55" y="155" as="geometry" />
</mxCell>
<mxCell id="7" parent="1" style="ellipse;whiteSpace=wrap;html=1;fillColor=#22C55E;strokeColor=#16A34A;strokeWidth=1;fontSize=14;fontStyle=1;fontColor=#FFFFFF;" value="1" vertex="1">
<mxGeometry height="30" width="30" x="65" y="165" as="geometry" />
</mxCell>
<mxCell id="8" parent="1" style="text;html=1;strokeColor=none;fillColor=none;align=left;verticalAlign=middle;fontSize=13;fontColor=#166534;fontStyle=1;spacingLeft=5;" value="局部变量、循环变量优先使用基本类型" vertex="1">
<mxGeometry height="22" width="310" x="100" y="160" as="geometry" />
</mxCell>
<mxCell id="9" parent="1" style="text;html=1;strokeColor=none;fillColor=#DCFCE7;align=left;verticalAlign=middle;fontSize=11;fontFamily=Courier New;fontColor=#166534;rounded=1;spacingLeft=8;" value="int count = 0; // ✓ 避免创建对象开销" vertex="1">
<mxGeometry height="20" width="240" x="100" y="183" as="geometry" />
</mxCell>
<mxCell id="10" parent="1" style="rounded=1;whiteSpace=wrap;html=1;fillColor=#FFFFFF;strokeColor=#BBF7D0;strokeWidth=1;" value="" vertex="1">
<mxGeometry height="55" width="370" x="55" y="217" as="geometry" />
</mxCell>
<mxCell id="11" parent="1" style="ellipse;whiteSpace=wrap;html=1;fillColor=#22C55E;strokeColor=#16A34A;strokeWidth=1;fontSize=14;fontStyle=1;fontColor=#FFFFFF;" value="2" vertex="1">
<mxGeometry height="30" width="30" x="65" y="227" as="geometry" />
</mxCell>
<mxCell id="12" parent="1" style="text;html=1;strokeColor=none;fillColor=none;align=left;verticalAlign=middle;fontSize=13;fontColor=#166534;fontStyle=1;spacingLeft=5;" value="需要放入集合 (Collection) 时使用包装类" vertex="1">
<mxGeometry height="22" width="280" x="100" y="222" as="geometry" />
</mxCell>
<mxCell id="13" parent="1" style="text;html=1;strokeColor=none;fillColor=#DCFCE7;align=left;verticalAlign=middle;fontSize=11;fontFamily=Courier New;fontColor=#166534;rounded=1;spacingLeft=8;" value="List<Integer> list; // 泛型不支持基本类型" vertex="1">
<mxGeometry height="20" width="260" x="100" y="245" as="geometry" />
</mxCell>
<mxCell id="14" parent="1" style="rounded=1;whiteSpace=wrap;html=1;fillColor=#FFFFFF;strokeColor=#BBF7D0;strokeWidth=1;" value="" vertex="1">
<mxGeometry height="55" width="370" x="55" y="279" as="geometry" />
</mxCell>
<mxCell id="15" parent="1" style="ellipse;whiteSpace=wrap;html=1;fillColor=#22C55E;strokeColor=#16A34A;strokeWidth=1;fontSize=14;fontStyle=1;fontColor=#FFFFFF;" value="3" vertex="1">
<mxGeometry height="30" width="30" x="65" y="289" as="geometry" />
</mxCell>
<mxCell id="16" parent="1" style="text;html=1;strokeColor=none;fillColor=none;align=left;verticalAlign=middle;fontSize=13;fontColor=#166534;fontStyle=1;spacingLeft=5;" value="需要表示 "无值/Null" 语义时使用包装类" vertex="1">
<mxGeometry height="22" width="280" x="100" y="284" as="geometry" />
</mxCell>
<mxCell id="17" parent="1" style="text;html=1;strokeColor=none;fillColor=#DCFCE7;align=left;verticalAlign=middle;fontSize=11;fontFamily=Courier New;fontColor=#166534;rounded=1;spacingLeft=8;" value="Integer age = null; // 表示"未知"" vertex="1">
<mxGeometry height="20" width="220" x="100" y="307" as="geometry" />
</mxCell>
<mxCell id="18" parent="1" style="rounded=1;whiteSpace=wrap;html=1;fillColor=#FFFFFF;strokeColor=#BBF7D0;strokeWidth=1;" value="" vertex="1">
<mxGeometry height="40" width="370" x="55" y="341" as="geometry" />
</mxCell>
<mxCell id="19" parent="1" style="ellipse;whiteSpace=wrap;html=1;fillColor=#22C55E;strokeColor=#16A34A;strokeWidth=1;fontSize=14;fontStyle=1;fontColor=#FFFFFF;" value="4" vertex="1">
<mxGeometry height="30" width="30" x="65" y="346" as="geometry" />
</mxCell>
<mxCell id="20" parent="1" style="text;html=1;strokeColor=none;fillColor=none;align=left;verticalAlign=middle;fontSize=13;fontColor=#166534;fontStyle=1;spacingLeft=5;" value="包装类型比较永远使用 equals()" vertex="1">
<mxGeometry height="22" width="280" x="100" y="350" as="geometry" />
</mxCell>
<mxCell id="22" parent="1" style="rounded=1;whiteSpace=wrap;html=1;fillColor=#FEF2F2;strokeColor=#EF4444;strokeWidth=2;arcSize=6;" value="" vertex="1">
<mxGeometry height="280" width="400" x="460" y="110" as="geometry" />
</mxCell>
<mxCell id="23" parent="1" style="text;html=1;strokeColor=none;fillColor=#EF4444;align=center;verticalAlign=middle;fontSize=15;fontStyle=1;fontColor=#FFFFFF;rounded=1;" value="❌ 避免做法 (DON'T)" vertex="1">
<mxGeometry height="32" width="160" x="460" y="110" as="geometry" />
</mxCell>
<mxCell id="24" parent="1" style="rounded=1;whiteSpace=wrap;html=1;fillColor=#FFFFFF;strokeColor=#FECACA;strokeWidth=1;" value="" vertex="1">
<mxGeometry height="70" width="370" x="475" y="155" as="geometry" />
</mxCell>
<mxCell id="25" parent="1" style="ellipse;whiteSpace=wrap;html=1;fillColor=#EF4444;strokeColor=#DC2626;strokeWidth=1;fontSize=14;fontStyle=1;fontColor=#FFFFFF;" value="1" vertex="1">
<mxGeometry height="30" width="30" x="485" y="175" as="geometry" />
</mxCell>
<mxCell id="26" parent="1" style="text;html=1;strokeColor=none;fillColor=none;align=left;verticalAlign=middle;fontSize=13;fontColor=#991B1B;fontStyle=1;spacingLeft=5;" value="循环体内使用包装类型做累加" vertex="1">
<mxGeometry height="22" width="280" x="520" y="160" as="geometry" />
</mxCell>
<mxCell id="27" parent="1" style="text;html=1;strokeColor=none;fillColor=#FEE2E2;align=left;verticalAlign=middle;fontSize=11;fontFamily=Courier New;fontColor=#991B1B;rounded=1;spacingLeft=8;" value="Long sum = 0L; // ✗ 定义为包装类" vertex="1">
<mxGeometry height="18" width="230" x="520" y="183" as="geometry" />
</mxCell>
<mxCell id="28" parent="1" style="text;html=1;strokeColor=none;fillColor=#FEE2E2;align=left;verticalAlign=middle;fontSize=11;fontFamily=Courier New;fontColor=#991B1B;rounded=1;spacingLeft=8;" value="for(...) sum += i; // ✗ 反复拆箱再装箱" vertex="1">
<mxGeometry height="18" width="260" x="520" y="202" as="geometry" />
</mxCell>
<mxCell id="29" parent="1" style="rounded=1;whiteSpace=wrap;html=1;fillColor=#FFFFFF;strokeColor=#FECACA;strokeWidth=1;" value="" vertex="1">
<mxGeometry height="75" width="370" x="475" y="235" as="geometry" />
</mxCell>
<mxCell id="30" parent="1" style="ellipse;whiteSpace=wrap;html=1;fillColor=#EF4444;strokeColor=#DC2626;strokeWidth=1;fontSize=14;fontStyle=1;fontColor=#FFFFFF;" value="2" vertex="1">
<mxGeometry height="30" width="30" x="485" y="255" as="geometry" />
</mxCell>
<mxCell id="31" parent="1" style="text;html=1;strokeColor=none;fillColor=none;align=left;verticalAlign=middle;fontSize=13;fontColor=#991B1B;fontStyle=1;spacingLeft=5;" value="用 == 比较包装类型" vertex="1">
<mxGeometry height="22" width="200" x="520" y="240" as="geometry" />
</mxCell>
<mxCell id="32" parent="1" style="text;html=1;strokeColor=none;fillColor=#FEE2E2;align=left;verticalAlign=middle;fontSize=11;fontFamily=Courier New;fontColor=#991B1B;rounded=1;spacingLeft=8;" value="a == b // ✗ 比较的是对象地址" vertex="1">
<mxGeometry height="18" width="220" x="520" y="265" as="geometry" />
</mxCell>
<mxCell id="33" parent="1" style="text;html=1;strokeColor=none;fillColor=none;align=left;verticalAlign=middle;fontSize=10;fontColor=#991B1B;spacingLeft=5;" value="(注：仅在缓存范围内 -128~127 有效，<br>超出范围则失效，极易产生 Bug)" vertex="1">
<mxGeometry height="24" width="280" x="520" y="285" as="geometry" />
</mxCell>
<mxCell id="34" parent="1" style="rounded=1;whiteSpace=wrap;html=1;fillColor=#FFFFFF;strokeColor=#FECACA;strokeWidth=1;" value="" vertex="1">
<mxGeometry height="60" width="370" x="475" y="320" as="geometry" />
</mxCell>
<mxCell id="35" parent="1" style="ellipse;whiteSpace=wrap;html=1;fillColor=#EF4444;strokeColor=#DC2626;strokeWidth=1;fontSize=14;fontStyle=1;fontColor=#FFFFFF;" value="3" vertex="1">
<mxGeometry height="30" width="30" x="485" y="335" as="geometry" />
</mxCell>
<mxCell id="36" parent="1" style="text;html=1;strokeColor=none;fillColor=none;align=left;verticalAlign=middle;fontSize=13;fontColor=#991B1B;fontStyle=1;spacingLeft=5;" value="局部变量不必要地使用包装类型" vertex="1">
<mxGeometry height="22" width="250" x="520" y="325" as="geometry" />
</mxCell>
<mxCell id="37" parent="1" style="text;html=1;strokeColor=none;fillColor=#FEE2E2;align=left;verticalAlign=middle;fontSize=11;fontFamily=Courier New;fontColor=#991B1B;rounded=1;spacingLeft=8;" value="Integer i = 0; // ✗ 增加了 GC 压力" vertex="1">
<mxGeometry height="18" width="220" x="520" y="352" as="geometry" />
</mxCell>
<mxCell id="39" parent="1" style="rounded=1;whiteSpace=wrap;html=1;fillColor=#EFF6FF;strokeColor=#3B82F6;strokeWidth=2;" value="" vertex="1">
<mxGeometry height="230" width="820" x="40" y="410" as="geometry" />
</mxCell>
<mxCell id="40" parent="1" style="text;html=1;strokeColor=none;fillColor=#3B82F6;align=center;verticalAlign=middle;fontSize=15;fontStyle=1;fontColor=#FFFFFF;rounded=1;" value="📝 实体类 (POJO/Entity) 属性定义原则" vertex="1">
<mxGeometry height="32" width="280" x="40" y="410" as="geometry" />
</mxCell>
<mxCell id="41" parent="1" style="rounded=1;whiteSpace=wrap;html=1;fillColor=#FFFFFF;strokeColor=#BFDBFE;strokeWidth=1;" value="" vertex="1">
<mxGeometry height="85" width="380" x="55" y="460" as="geometry" />
</mxCell>
<mxCell id="42" parent="1" style="text;html=1;strokeColor=none;fillColor=#DBEAFE;align=center;verticalAlign=middle;fontSize=12;fontStyle=1;fontColor=#1E40AF;rounded=1;" value="场景：数据库字段允许为 NULL" vertex="1">
<mxGeometry height="24" width="180" x="70" y="470" as="geometry" />
</mxCell>
<mxCell id="43" parent="1" style="text;html=1;strokeColor=none;fillColor=none;align=center;verticalAlign=middle;fontSize=24;fontStyle=1;fontColor=#3B82F6;" value="→" vertex="1">
<mxGeometry height="28" width="30" x="250" y="470" as="geometry" />
</mxCell>
<mxCell id="44" parent="1" style="text;html=1;strokeColor=none;fillColor=#22C55E;align=center;verticalAlign=middle;fontSize=12;fontStyle=1;fontColor=#FFFFFF;rounded=1;" value="必须使用包装类型" vertex="1">
<mxGeometry height="24" width="120" x="290" y="470" as="geometry" />
</mxCell>
<mxCell id="45" parent="1" style="text;html=1;strokeColor=none;fillColor=#F0FDF4;align=left;verticalAlign=middle;fontSize=11;fontFamily=Courier New;fontColor=#166534;rounded=1;spacingLeft=8;" value="private Integer age; // 如果用 int 接收 null<br>// 会报 NullPointerException" vertex="1">
<mxGeometry height="30" width="340" x="70" y="505" as="geometry" />
</mxCell>
<mxCell id="46" parent="1" style="rounded=1;whiteSpace=wrap;html=1;fillColor=#FFFFFF;strokeColor=#BFDBFE;strokeWidth=1;" value="" vertex="1">
<mxGeometry height="85" width="390" x="455" y="460" as="geometry" />
</mxCell>
<mxCell id="47" parent="1" style="text;html=1;strokeColor=none;fillColor=#DBEAFE;align=center;verticalAlign=middle;fontSize=12;fontStyle=1;fontColor=#1E40AF;rounded=1;" value="场景：字段非空 (NOT NULL) 且有默认值" vertex="1">
<mxGeometry height="24" width="220" x="470" y="470" as="geometry" />
</mxCell>
<mxCell id="48" parent="1" style="text;html=1;strokeColor=none;fillColor=none;align=center;verticalAlign=middle;fontSize=24;fontStyle=1;fontColor=#3B82F6;" value="→" vertex="1">
<mxGeometry height="28" width="30" x="690" y="470" as="geometry" />
</mxCell>
<mxCell id="49" parent="1" style="text;html=1;strokeColor=none;fillColor=#F59E0B;align=center;verticalAlign=middle;fontSize=12;fontStyle=1;fontColor=#FFFFFF;rounded=1;" value="可用基本类型<div>&nbsp;(视团队规范)</div>" vertex="1">
<mxGeometry height="34" width="120" x="720" y="465" as="geometry" />
</mxCell>
<mxCell id="50" parent="1" style="text;html=1;strokeColor=none;fillColor=#FFFBEB;align=left;verticalAlign=middle;fontSize=11;fontFamily=Courier New;fontColor=#92400E;rounded=1;spacingLeft=8;" value="private int status; // 省略了 null 检查<br>// 默认值为 0" vertex="1">
<mxGeometry height="30" width="360" x="470" y="505" as="geometry" />
</mxCell>
<mxCell id="51" parent="1" style="rounded=1;whiteSpace=wrap;html=1;fillColor=#FAF5FF;strokeColor=#8B5CF6;strokeWidth=2;arcSize=4;" value="" vertex="1">
<mxGeometry height="65" width="790" x="55" y="560" as="geometry" />
</mxCell>
<mxCell id="52" parent="1" style="text;html=1;strokeColor=none;fillColor=#8B5CF6;align=center;verticalAlign=middle;fontSize=13;fontStyle=1;fontColor=#FFFFFF;rounded=1;" value="📚 阿里巴巴 Java 开发手册建议" vertex="1">
<mxGeometry height="26" width="200" x="55" y="560" as="geometry" />
</mxCell>
<mxCell id="53" parent="1" style="text;html=1;strokeColor=none;fillColor=none;align=left;verticalAlign=middle;fontSize=13;fontStyle=1;fontColor=#6D28D9;spacingLeft=15;" value="【强制】所有的 POJO 类属性必须使用包装数据类型" vertex="1">
<mxGeometry height="25" width="400" x="60" y="590" as="geometry" />
</mxCell>
<mxCell id="54" parent="1" style="text;html=1;strokeColor=none;fillColor=#F3E8FF;align=left;verticalAlign=middle;fontSize=12;fontColor=#6D28D9;rounded=1;spacingLeft=10;" value="原因：RPC 调用的返回值和数据库查询结果可能为 null" vertex="1">
<mxGeometry height="25" width="380" x="450" y="590" as="geometry" />
</mxCell>
<mxCell id="55" parent="1" style="rounded=1;whiteSpace=wrap;html=1;fillColor=#FFFBEB;strokeColor=#F59E0B;strokeWidth=2;" value="" vertex="1">
<mxGeometry height="140" width="820" x="40" y="660" as="geometry" />
</mxCell>
<mxCell id="56" parent="1" style="text;html=1;strokeColor=none;fillColor=#F59E0B;align=center;verticalAlign=middle;fontSize=15;fontStyle=1;fontColor=#FFFFFF;rounded=1;" value="⚡ 性能对比 (Performance)" vertex="1">
<mxGeometry height="28" width="200" x="40" y="660" as="geometry" />
</mxCell>
<mxCell id="57" parent="1" style="rounded=1;whiteSpace=wrap;html=1;fillColor=#FEF2F2;strokeColor=#FECACA;strokeWidth=1;" value="" vertex="1">
<mxGeometry height="80" width="370" x="55" y="705" as="geometry" />
</mxCell>
<mxCell id="58" parent="1" style="text;html=1;strokeColor=none;fillColor=#EF4444;align=center;verticalAlign=middle;fontSize=12;fontStyle=1;fontColor=#FFFFFF;rounded=1;" value="❌ 慢 (约 6000ms)" vertex="1">
<mxGeometry height="22" width="120" x="65" y="715" as="geometry" />
</mxCell>
<mxCell id="59" parent="1" style="text;html=1;strokeColor=none;fillColor=#FFFFFF;align=left;verticalAlign=middle;fontSize=11;fontFamily=Courier New;fontColor=#991B1B;rounded=1;spacingLeft=8;" value="Long sum = 0L;<br>for(long i=0; i < Integer.MAX_VALUE; i++)<br> sum += i; // 每次 += 都在创建新对象" vertex="1">
<mxGeometry height="38" width="350" x="65" y="740" as="geometry" />
</mxCell>
<mxCell id="60" parent="1" style="rounded=1;whiteSpace=wrap;html=1;fillColor=#F0FDF4;strokeColor=#BBF7D0;strokeWidth=1;" value="" vertex="1">
<mxGeometry height="80" width="400" x="445" y="705" as="geometry" />
</mxCell>
<mxCell id="61" parent="1" style="text;html=1;strokeColor=none;fillColor=#22C55E;align=center;verticalAlign=middle;fontSize=12;fontStyle=1;fontColor=#FFFFFF;rounded=1;" value="✅ 快 (约 600ms)" vertex="1">
<mxGeometry height="22" width="120" x="455" y="715" as="geometry" />
</mxCell>
<mxCell id="62" parent="1" style="text;html=1;strokeColor=none;fillColor=#FFFFFF;align=left;verticalAlign=middle;fontSize=11;fontFamily=Courier New;fontColor=#166534;rounded=1;spacingLeft=8;" value="long sum = 0L; // 使用基本类型<br>for(long i=0; i < Integer.MAX_VALUE; i++)<br> sum += i; // 纯数值计算，无对象创建" vertex="1">
<mxGeometry height="38" width="380" x="455" y="740" as="geometry" />
</mxCell>
<mxCell id="63" parent="1" style="text;html=1;strokeColor=none;fillColor=#8B5CF6;align=center;verticalAlign=middle;fontSize=18;fontStyle=1;fontColor=#FFFFFF;rounded=1;" value="10x" vertex="1">
<mxGeometry height="26" width="50" x="590" y="670" as="geometry" />
</mxCell>
<mxCell id="64" parent="1" style="text;html=1;strokeColor=none;fillColor=none;align=center;verticalAlign=middle;fontSize=12;fontStyle=1;fontColor=#8B5CF6;" value="Faster" vertex="1">
<mxGeometry height="22" width="50" x="645" y="672" as="geometry" />
</mxCell>
</root>
</mxGraphModel>
</diagram>
</mxfile>
八、BigDecimal 精确计算
8.1 为什么需要 BigDecimal
public class WhyBigDecimalDemo {
public static void main(String[] args) {
// ═══════════════════════════════════════════════════════════════
// 浮点数不适合金融计算
// ═══════════════════════════════════════════════════════════════
double price = 0.1;
double quantity = 0.2;
double total = price + quantity;
System.out.println("0.1 + 0.2 = " + total);
// 输出: 0.30000000000000004
// 如果这是钱...
double money = 1.0 - 0.9;
System.out.println("1.0 - 0.9 = " + money);
// 输出: 0.09999999999999998
// 累计误差
double sum = 0;
for (int i = 0; i < 10; i++) {
sum += 0.1;
}
System.out.println("0.1 × 10 = " + sum);
// 输出: 0.9999999999999999
}
}
8.2 BigDecimal 基本用法
import java.math.BigDecimal;
import java.math.RoundingMode;
public class BigDecimalBasicDemo {
public static void main(String[] args) {
// ═══════════════════════════════════════════════════════════════
// 创建 BigDecimal（推荐使用 String 构造器）
// ═══════════════════════════════════════════════════════════════
// ✅ 推荐：String 构造器，精确
BigDecimal a = new BigDecimal("0.1");
BigDecimal b = new BigDecimal("0.2");
// ❌ 不推荐：double 构造器，已经有精度问题
BigDecimal bad = new BigDecimal(0.1);
System.out.println("String构造: " + a); // 0.1
System.out.println("Double构造: " + bad); // 0.1000000000000000055511151231257827021181...
// ✅ 或使用 valueOf（内部转为 String）
BigDecimal c = BigDecimal.valueOf(0.1);
// ═══════════════════════════════════════════════════════════════
// 四则运算
// ═══════════════════════════════════════════════════════════════
BigDecimal x = new BigDecimal("10");
BigDecimal y = new BigDecimal("3");
System.out.println("加法: " + x.add(y)); // 13
System.out.println("减法: " + x.subtract(y)); // 7
System.out.println("乘法: " + x.multiply(y)); // 30
// 除法必须指定精度，否则除不尽会抛异常
// System.out.println(x.divide(y)); // ❌ ArithmeticException
System.out.println("除法: " + x.divide(y, 2, RoundingMode.HALF_UP)); // 3.33
// ═══════════════════════════════════════════════════════════════
// 精度和舍入模式
// ═══════════════════════════════════════════════════════════════
BigDecimal value = new BigDecimal("3.1415926");
// 保留 2 位小数，四舍五入
BigDecimal rounded = value.setScale(2, RoundingMode.HALF_UP);
System.out.println("四舍五入: " + rounded); // 3.14
// 向上取整
System.out.println("向上取整: " + value.setScale(2, RoundingMode.UP)); // 3.15
// 向下取整
System.out.println("向下取整: " + value.setScale(2, RoundingMode.DOWN)); // 3.14
// 银行家舍入（四舍六入五成双）
System.out.println("银行家舍入: " + new BigDecimal("2.5").setScale(0, RoundingMode.HALF_EVEN)); // 2
System.out.println("银行家舍入: " + new BigDecimal("3.5").setScale(0, RoundingMode.HALF_EVEN)); // 4
}
}
8.3 舍入模式详解
<mxfile>
<diagram id="bigdecimal-rounding-modes" name="BigDecimal舍入模式">
<mxGraphModel dx="900" dy="750" grid="1" gridSize="10" guides="1" tooltips="1" connect="1" arrows="1" fold="1" page="1" pageScale="1" pageWidth="900" pageHeight="750">
<root>
<mxCell id="0" />
<mxCell id="1" parent="0" />
<mxCell id="2" value="BigDecimal 舍入模式" style="text;html=1;strokeColor=none;fillColor=none;align=center;verticalAlign=middle;fontSize=26;fontStyle=1;fontColor=#1E293B;" vertex="1" parent="1">
<mxGeometry x="250" y="15" width="400" height="40" as="geometry" />
</mxCell>
<mxCell id="3" value="RoundingMode 枚举详解" style="text;html=1;strokeColor=none;fillColor=#6366F1;align=center;verticalAlign=middle;fontSize=13;fontColor=#FFFFFF;rounded=1;" vertex="1" parent="1">
<mxGeometry x="335" y="55" width="230" height="26" as="geometry" />
</mxCell>
<mxCell id="4" value="" style="rounded=1;whiteSpace=wrap;html=1;fillColor=#F8FAFC;strokeColor=#E2E8F0;strokeWidth=2;" vertex="1" parent="1">
<mxGeometry x="40" y="95" width="820" height="520" as="geometry" />
</mxCell>
<mxCell id="5" value="RoundingMode" style="rounded=0;whiteSpace=wrap;html=1;fillColor=#1E293B;strokeColor=#0F172A;strokeWidth=1;fontSize=14;fontStyle=1;fontColor=#FFFFFF;" vertex="1" parent="1">
<mxGeometry x="55" y="110" width="150" height="38" as="geometry" />
</mxCell>
<mxCell id="6" value="说明" style="rounded=0;whiteSpace=wrap;html=1;fillColor=#1E293B;strokeColor=#0F172A;strokeWidth=1;fontSize=14;fontStyle=1;fontColor=#FFFFFF;" vertex="1" parent="1">
<mxGeometry x="205" y="110" width="280" height="38" as="geometry" />
</mxCell>
<mxCell id="7" value="示例" style="rounded=0;whiteSpace=wrap;html=1;fillColor=#1E293B;strokeColor=#0F172A;strokeWidth=1;fontSize=14;fontStyle=1;fontColor=#FFFFFF;" vertex="1" parent="1">
<mxGeometry x="485" y="110" width="200" height="38" as="geometry" />
</mxCell>
<mxCell id="8" value="方向" style="rounded=0;whiteSpace=wrap;html=1;fillColor=#1E293B;strokeColor=#0F172A;strokeWidth=1;fontSize=14;fontStyle=1;fontColor=#FFFFFF;" vertex="1" parent="1">
<mxGeometry x="685" y="110" width="160" height="38" as="geometry" />
</mxCell>
<mxCell id="9" value="UP" style="rounded=0;whiteSpace=wrap;html=1;fillColor=#DBEAFE;strokeColor=#BFDBFE;strokeWidth=1;fontSize=14;fontStyle=1;fontColor=#1E40AF;fontFamily=Courier New;" vertex="1" parent="1">
<mxGeometry x="55" y="148" width="150" height="50" as="geometry" />
</mxCell>
<mxCell id="10" value="远离零方向舍入<br>（绝对值变大）" style="rounded=0;whiteSpace=wrap;html=1;fillColor=#EFF6FF;strokeColor=#BFDBFE;strokeWidth=1;fontSize=12;fontColor=#1E40AF;" vertex="1" parent="1">
<mxGeometry x="205" y="148" width="280" height="50" as="geometry" />
</mxCell>
<mxCell id="11" value="2.5 → 3<br>-2.5 → -3" style="rounded=0;whiteSpace=wrap;html=1;fillColor=#EFF6FF;strokeColor=#BFDBFE;strokeWidth=1;fontSize=12;fontFamily=Courier New;fontColor=#1E40AF;fontStyle=1;" vertex="1" parent="1">
<mxGeometry x="485" y="148" width="200" height="50" as="geometry" />
</mxCell>
<mxCell id="12" value="← 0 →" style="rounded=0;whiteSpace=wrap;html=1;fillColor=#EFF6FF;strokeColor=#BFDBFE;strokeWidth=1;fontSize=18;fontStyle=1;fontColor=#3B82F6;" vertex="1" parent="1">
<mxGeometry x="685" y="148" width="160" height="50" as="geometry" />
</mxCell>
<mxCell id="13" value="DOWN" style="rounded=0;whiteSpace=wrap;html=1;fillColor=#FEF3C7;strokeColor=#FDE68A;strokeWidth=1;fontSize=14;fontStyle=1;fontColor=#92400E;fontFamily=Courier New;" vertex="1" parent="1">
<mxGeometry x="55" y="198" width="150" height="50" as="geometry" />
</mxCell>
<mxCell id="14" value="趋向零方向舍入<br>（截断小数部分）" style="rounded=0;whiteSpace=wrap;html=1;fillColor=#FFFBEB;strokeColor=#FDE68A;strokeWidth=1;fontSize=12;fontColor=#92400E;" vertex="1" parent="1">
<mxGeometry x="205" y="198" width="280" height="50" as="geometry" />
</mxCell>
<mxCell id="15" value="2.5 → 2<br>-2.5 → -2" style="rounded=0;whiteSpace=wrap;html=1;fillColor=#FFFBEB;strokeColor=#FDE68A;strokeWidth=1;fontSize=12;fontFamily=Courier New;fontColor=#92400E;fontStyle=1;" vertex="1" parent="1">
<mxGeometry x="485" y="198" width="200" height="50" as="geometry" />
</mxCell>
<mxCell id="16" value="→ 0 ←" style="rounded=0;whiteSpace=wrap;html=1;fillColor=#FFFBEB;strokeColor=#FDE68A;strokeWidth=1;fontSize=18;fontStyle=1;fontColor=#F59E0B;" vertex="1" parent="1">
<mxGeometry x="685" y="198" width="160" height="50" as="geometry" />
</mxCell>
<mxCell id="17" value="CEILING" style="rounded=0;whiteSpace=wrap;html=1;fillColor=#DCFCE7;strokeColor=#BBF7D0;strokeWidth=1;fontSize=14;fontStyle=1;fontColor=#166534;fontFamily=Courier New;" vertex="1" parent="1">
<mxGeometry x="55" y="248" width="150" height="50" as="geometry" />
</mxCell>
<mxCell id="18" value="向正无穷方向舍入<br>（天花板）" style="rounded=0;whiteSpace=wrap;html=1;fillColor=#F0FDF4;strokeColor=#BBF7D0;strokeWidth=1;fontSize=12;fontColor=#166534;" vertex="1" parent="1">
<mxGeometry x="205" y="248" width="280" height="50" as="geometry" />
</mxCell>
<mxCell id="19" value="2.5 → 3<br>-2.5 → -2" style="rounded=0;whiteSpace=wrap;html=1;fillColor=#F0FDF4;strokeColor=#BBF7D0;strokeWidth=1;fontSize=12;fontFamily=Courier New;fontColor=#166534;fontStyle=1;" vertex="1" parent="1">
<mxGeometry x="485" y="248" width="200" height="50" as="geometry" />
</mxCell>
<mxCell id="20" value="→ +∞" style="rounded=0;whiteSpace=wrap;html=1;fillColor=#F0FDF4;strokeColor=#BBF7D0;strokeWidth=1;fontSize=18;fontStyle=1;fontColor=#22C55E;" vertex="1" parent="1">
<mxGeometry x="685" y="248" width="160" height="50" as="geometry" />
</mxCell>
<mxCell id="21" value="FLOOR" style="rounded=0;whiteSpace=wrap;html=1;fillColor=#F3E8FF;strokeColor=#E9D5FF;strokeWidth=1;fontSize=14;fontStyle=1;fontColor=#6D28D9;fontFamily=Courier New;" vertex="1" parent="1">
<mxGeometry x="55" y="298" width="150" height="50" as="geometry" />
</mxCell>
<mxCell id="22" value="向负无穷方向舍入<br>（地板）" style="rounded=0;whiteSpace=wrap;html=1;fillColor=#FAF5FF;strokeColor=#E9D5FF;strokeWidth=1;fontSize=12;fontColor=#6D28D9;" vertex="1" parent="1">
<mxGeometry x="205" y="298" width="280" height="50" as="geometry" />
</mxCell>
<mxCell id="23" value="2.5 → 2<br>-2.5 → -3" style="rounded=0;whiteSpace=wrap;html=1;fillColor=#FAF5FF;strokeColor=#E9D5FF;strokeWidth=1;fontSize=12;fontFamily=Courier New;fontColor=#6D28D9;fontStyle=1;" vertex="1" parent="1">
<mxGeometry x="485" y="298" width="200" height="50" as="geometry" />
</mxCell>
<mxCell id="24" value="← -∞" style="rounded=0;whiteSpace=wrap;html=1;fillColor=#FAF5FF;strokeColor=#E9D5FF;strokeWidth=1;fontSize=18;fontStyle=1;fontColor=#8B5CF6;" vertex="1" parent="1">
<mxGeometry x="685" y="298" width="160" height="50" as="geometry" />
</mxCell>
<mxCell id="25" value="HALF_UP" style="rounded=0;whiteSpace=wrap;html=1;fillColor=#FEE2E2;strokeColor=#FECACA;strokeWidth=2;fontSize=14;fontStyle=1;fontColor=#991B1B;fontFamily=Courier New;" vertex="1" parent="1">
<mxGeometry x="55" y="348" width="150" height="50" as="geometry" />
</mxCell>
<mxCell id="26" value="四舍五入 ⭐<br>（最常用）" style="rounded=0;whiteSpace=wrap;html=1;fillColor=#FEF2F2;strokeColor=#FECACA;strokeWidth=2;fontSize=12;fontStyle=1;fontColor=#991B1B;" vertex="1" parent="1">
<mxGeometry x="205" y="348" width="280" height="50" as="geometry" />
</mxCell>
<mxCell id="27" value="2.5 → 3<br>2.4 → 2" style="rounded=0;whiteSpace=wrap;html=1;fillColor=#FEF2F2;strokeColor=#FECACA;strokeWidth=2;fontSize=12;fontFamily=Courier New;fontColor=#991B1B;fontStyle=1;" vertex="1" parent="1">
<mxGeometry x="485" y="348" width="200" height="50" as="geometry" />
</mxCell>
<mxCell id="28" value="≥0.5 进位" style="rounded=0;whiteSpace=wrap;html=1;fillColor=#FEF2F2;strokeColor=#FECACA;strokeWidth=2;fontSize=13;fontStyle=1;fontColor=#EF4444;" vertex="1" parent="1">
<mxGeometry x="685" y="348" width="160" height="50" as="geometry" />
</mxCell>
<mxCell id="29" value="HALF_DOWN" style="rounded=0;whiteSpace=wrap;html=1;fillColor=#E0E7FF;strokeColor=#C7D2FE;strokeWidth=1;fontSize=14;fontStyle=1;fontColor=#3730A3;fontFamily=Courier New;" vertex="1" parent="1">
<mxGeometry x="55" y="398" width="150" height="50" as="geometry" />
</mxCell>
<mxCell id="30" value="五舍六入<br>（0.5 舍去）" style="rounded=0;whiteSpace=wrap;html=1;fillColor=#EEF2FF;strokeColor=#C7D2FE;strokeWidth=1;fontSize=12;fontColor=#3730A3;" vertex="1" parent="1">
<mxGeometry x="205" y="398" width="280" height="50" as="geometry" />
</mxCell>
<mxCell id="31" value="2.5 → 2<br>2.6 → 3" style="rounded=0;whiteSpace=wrap;html=1;fillColor=#EEF2FF;strokeColor=#C7D2FE;strokeWidth=1;fontSize=12;fontFamily=Courier New;fontColor=#3730A3;fontStyle=1;" vertex="1" parent="1">
<mxGeometry x="485" y="398" width="200" height="50" as="geometry" />
</mxCell>
<mxCell id="32" value=">0.5 进位" style="rounded=0;whiteSpace=wrap;html=1;fillColor=#EEF2FF;strokeColor=#C7D2FE;strokeWidth=1;fontSize=13;fontStyle=1;fontColor=#6366F1;" vertex="1" parent="1">
<mxGeometry x="685" y="398" width="160" height="50" as="geometry" />
</mxCell>
<mxCell id="33" value="HALF_EVEN" style="rounded=0;whiteSpace=wrap;html=1;fillColor=#D1FAE5;strokeColor=#6EE7B7;strokeWidth=2;fontSize=14;fontStyle=1;fontColor=#065F46;fontFamily=Courier New;" vertex="1" parent="1">
<mxGeometry x="55" y="448" width="150" height="50" as="geometry" />
</mxCell>
<mxCell id="34" value="银行家舍入 💰<br>（四舍六入五成双）" style="rounded=0;whiteSpace=wrap;html=1;fillColor=#ECFDF5;strokeColor=#6EE7B7;strokeWidth=2;fontSize=12;fontStyle=1;fontColor=#065F46;" vertex="1" parent="1">
<mxGeometry x="205" y="448" width="280" height="50" as="geometry" />
</mxCell>
<mxCell id="35" value="2.5 → 2<br>3.5 → 4" style="rounded=0;whiteSpace=wrap;html=1;fillColor=#ECFDF5;strokeColor=#6EE7B7;strokeWidth=2;fontSize=12;fontFamily=Courier New;fontColor=#065F46;fontStyle=1;" vertex="1" parent="1">
<mxGeometry x="485" y="448" width="200" height="50" as="geometry" />
</mxCell>
<mxCell id="36" value="0.5 向偶数" style="rounded=0;whiteSpace=wrap;html=1;fillColor=#ECFDF5;strokeColor=#6EE7B7;strokeWidth=2;fontSize=13;fontStyle=1;fontColor=#10B981;" vertex="1" parent="1">
<mxGeometry x="685" y="448" width="160" height="50" as="geometry" />
</mxCell>
<mxCell id="37" value="UNNECESSARY" style="rounded=0;whiteSpace=wrap;html=1;fillColor=#FEF9C3;strokeColor=#FDE047;strokeWidth=1;fontSize=13;fontStyle=1;fontColor=#854D0E;fontFamily=Courier New;" vertex="1" parent="1">
<mxGeometry x="55" y="498" width="150" height="50" as="geometry" />
</mxCell>
<mxCell id="38" value="断言精确结果<br>否则抛 ArithmeticException" style="rounded=0;whiteSpace=wrap;html=1;fillColor=#FEFCE8;strokeColor=#FDE047;strokeWidth=1;fontSize=12;fontColor=#854D0E;" vertex="1" parent="1">
<mxGeometry x="205" y="498" width="280" height="50" as="geometry" />
</mxCell>
<mxCell id="39" value="1.0 → 1 ✓<br>1.5 → 异常 ✗" style="rounded=0;whiteSpace=wrap;html=1;fillColor=#FEFCE8;strokeColor=#FDE047;strokeWidth=1;fontSize=12;fontFamily=Courier New;fontColor=#854D0E;fontStyle=1;" vertex="1" parent="1">
<mxGeometry x="485" y="498" width="200" height="50" as="geometry" />
</mxCell>
<mxCell id="40" value="必须精确" style="rounded=0;whiteSpace=wrap;html=1;fillColor=#FEFCE8;strokeColor=#FDE047;strokeWidth=1;fontSize=13;fontStyle=1;fontColor=#EAB308;" vertex="1" parent="1">
<mxGeometry x="685" y="498" width="160" height="50" as="geometry" />
</mxCell>
<mxCell id="41" value="常用" style="text;html=1;strokeColor=none;fillColor=#EF4444;align=center;verticalAlign=middle;fontSize=10;fontStyle=1;fontColor=#FFFFFF;rounded=1;" vertex="1" parent="1">
<mxGeometry x="170" y="353" width="32" height="18" as="geometry" />
</mxCell>
<mxCell id="42" value="推荐" style="text;html=1;strokeColor=none;fillColor=#10B981;align=center;verticalAlign=middle;fontSize=10;fontStyle=1;fontColor=#FFFFFF;rounded=1;" vertex="1" parent="1">
<mxGeometry x="170" y="453" width="32" height="18" as="geometry" />
</mxCell>
<mxCell id="43" value="" style="rounded=1;whiteSpace=wrap;html=1;fillColor=#ECFDF5;strokeColor=#10B981;strokeWidth=2;" vertex="1" parent="1">
<mxGeometry x="40" y="630" width="820" height="100" as="geometry" />
</mxCell>
<mxCell id="44" value="💡 金融计算推荐" style="text;html=1;strokeColor=none;fillColor=#10B981;align=center;verticalAlign=middle;fontSize=14;fontStyle=1;fontColor=#FFFFFF;rounded=1;" vertex="1" parent="1">
<mxGeometry x="60" y="645" width="140" height="28" as="geometry" />
</mxCell>
<mxCell id="45" value="HALF_EVEN（银行家舍入）— 统计学上最公平，避免系统性偏差" style="text;html=1;strokeColor=none;fillColor=none;align=left;verticalAlign=middle;fontSize=14;fontStyle=1;fontColor=#065F46;spacingLeft=10;" vertex="1" parent="1">
<mxGeometry x="210" y="645" width="500" height="28" as="geometry" />
</mxCell>
<mxCell id="46" value="原理：当小数部分恰好为 0.5 时，向最近的偶数舍入，长期累计误差趋近于零" style="text;html=1;strokeColor=none;fillColor=#D1FAE5;align=left;verticalAlign=middle;fontSize=12;fontColor=#065F46;rounded=1;spacingLeft=10;" vertex="1" parent="1">
<mxGeometry x="60" y="685" width="520" height="28" as="geometry" />
</mxCell>
<mxCell id="47" value="bd.setScale(2, RoundingMode.HALF_EVEN)" style="text;html=1;strokeColor=none;fillColor=#065F46;align=center;verticalAlign=middle;fontSize=11;fontFamily=Courier New;fontStyle=1;fontColor=#FFFFFF;rounded=1;" vertex="1" parent="1">
<mxGeometry x="590" y="688" width="255" height="24" as="geometry" />
</mxCell>
</root>
</mxGraphModel>
</diagram>
</mxfile>
8.4 BigDecimal 比较
public class BigDecimalCompareDemo {
public static void main(String[] args) {
BigDecimal a = new BigDecimal("1.0");
BigDecimal b = new BigDecimal("1.00");
// ═══════════════════════════════════════════════════════════════
// equals() 比较值和精度（标度）
// ═══════════════════════════════════════════════════════════════
System.out.println("a.equals(b): " + a.equals(b)); // false！
// 因为 1.0 的标度是 1，1.00 的标度是 2
// ═══════════════════════════════════════════════════════════════
// compareTo() 只比较数值大小（推荐）
// ═══════════════════════════════════════════════════════════════
System.out.println("a.compareTo(b): " + a.compareTo(b)); // 0
// 0 表示相等，正数表示 a > b，负数表示 a < b
// 正确的相等判断
if (a.compareTo(b) == 0) {
System.out.println("a 和 b 数值相等");
}
// ═══════════════════════════════════════════════════════════════
// 使用 stripTrailingZeros() 去除尾部零后比较
// ═══════════════════════════════════════════════════════════════
BigDecimal c = new BigDecimal("1.0").stripTrailingZeros();
BigDecimal d = new BigDecimal("1.00").stripTrailingZeros();
System.out.println("stripTrailingZeros后 equals: " + c.equals(d)); // true
}
}
<mxfile>
<diagram id="bigdecimal-compare" name="BigDecimal equals vs compareTo">
<mxGraphModel dx="926" dy="817" grid="1" gridSize="10" guides="1" tooltips="1" connect="1" arrows="1" fold="1" page="1" pageScale="1" pageWidth="900" pageHeight="720" math="0" shadow="0">
<root>
<mxCell id="0" />
<mxCell id="1" parent="0" />
<mxCell id="2" parent="1" style="rounded=1;whiteSpace=wrap;html=1;fillColor=#fafafa;strokeColor=#7b1fa2;strokeWidth=3;shadow=1;" value="" vertex="1">
<mxGeometry height="730" width="820" x="40" y="20" as="geometry" />
</mxCell>
<mxCell id="3" parent="1" style="text;html=1;strokeColor=none;fillColor=none;align=center;verticalAlign=middle;whiteSpace=wrap;rounded=0;fontSize=26;fontStyle=1;fontColor=#4a148c;" value="BigDecimal equals vs compareTo" vertex="1">
<mxGeometry height="45" width="500" x="200" y="35" as="geometry" />
</mxCell>
<mxCell id="4" parent="1" style="rounded=1;whiteSpace=wrap;html=1;fillColor=#f3e5f5;strokeColor=#9c27b0;strokeWidth=2;" value="" vertex="1">
<mxGeometry height="205" width="780" x="60" y="95" as="geometry" />
</mxCell>
<mxCell id="5" parent="1" style="rounded=1;whiteSpace=wrap;html=1;fillColor=#9c27b0;strokeColor=none;" value="" vertex="1">
<mxGeometry height="40" width="780" x="60" y="95" as="geometry" />
</mxCell>
<mxCell id="6" parent="1" style="text;html=1;strokeColor=none;fillColor=none;align=center;verticalAlign=middle;whiteSpace=wrap;rounded=0;fontSize=17;fontStyle=1;fontColor=#ffffff;" value="🔍 BigDecimal 的内部表示" vertex="1">
<mxGeometry height="40" width="780" x="60" y="95" as="geometry" />
</mxCell>
<mxCell id="7" parent="1" style="rounded=1;whiteSpace=wrap;html=1;fillColor=#ffffff;strokeColor=#ce93d8;strokeWidth=2;shadow=1;" value="" vertex="1">
<mxGeometry height="45" width="720" x="90" y="150" as="geometry" />
</mxCell>
<mxCell id="8" parent="1" style="text;html=1;strokeColor=none;fillColor=none;align=center;verticalAlign=middle;whiteSpace=wrap;rounded=0;fontSize=16;" value="<font face="Courier New" style="font-size: 16px;">BigDecimal = <font color="#1565c0"><b>unscaledValue</b></font> × 10<sup>(<font color="#c62828"><b>-scale</b></font>)</sup></font>" vertex="1">
<mxGeometry height="45" width="720" x="90" y="150" as="geometry" />
</mxCell>
<mxCell id="9" parent="1" style="rounded=1;whiteSpace=wrap;html=1;fillColor=#e3f2fd;strokeColor=#1976d2;strokeWidth=2;" value="" vertex="1">
<mxGeometry height="70" width="350" x="90" y="210" as="geometry" />
</mxCell>
<mxCell id="10" parent="1" style="text;html=1;strokeColor=none;fillColor=none;align=left;verticalAlign=middle;whiteSpace=wrap;rounded=0;fontSize=13;spacingLeft=15;" value="<div style="text-align: left;"><font face="Courier New"><b style="font-size: 15px;">1.0</b><font style="font-size: 14px;"> = 10 × 10<sup>-1</sup></font></font></div><div style="text-align: left;"><font color="#1565c0">unscaledValue = <b>10</b></font></div><div style="text-align: left;"><font color="#c62828">scale = <b>1</b></font></div>" vertex="1">
<mxGeometry height="70" width="350" x="90" y="210" as="geometry" />
</mxCell>
<mxCell id="11" parent="1" style="rounded=1;whiteSpace=wrap;html=1;fillColor=#fff3e0;strokeColor=#ff9800;strokeWidth=2;" value="" vertex="1">
<mxGeometry height="70" width="350" x="460" y="210" as="geometry" />
</mxCell>
<mxCell id="12" parent="1" style="text;html=1;strokeColor=none;fillColor=none;align=left;verticalAlign=middle;whiteSpace=wrap;rounded=0;fontSize=13;spacingLeft=15;" value="<div style="text-align: left;"><font face="Courier New"><b style="font-size: 15px;">1.00</b><font style="font-size: 14px;"> = 100 × 10<sup>-2</sup></font></font></div><div style="text-align: left;"><font color="#1565c0">unscaledValue = <b>100</b></font></div><div style="text-align: left;"><font color="#c62828">scale = <b>2</b></font></div>" vertex="1">
<mxGeometry height="70" width="350" x="460" y="210" as="geometry" />
</mxCell>
<mxCell id="13" parent="1" style="text;html=1;strokeColor=none;fillColor=none;align=center;verticalAlign=middle;whiteSpace=wrap;rounded=0;fontSize=24;fontStyle=1;fontColor=#e53935;" value="≠" vertex="1">
<mxGeometry height="40" width="40" x="430" y="225" as="geometry" />
</mxCell>
<mxCell id="14" parent="1" style="text;html=1;strokeColor=none;fillColor=none;align=center;verticalAlign=middle;whiteSpace=wrap;rounded=0;fontSize=13;fontColor=#7b1fa2;fontStyle=1;" value="⚠️ 两者数值相等，但内部表示不同！" vertex="1">
<mxGeometry height="20" width="340" x="280" y="280" as="geometry" />
</mxCell>
<mxCell id="15" parent="1" style="rounded=1;whiteSpace=wrap;html=1;fillColor=#ffebee;strokeColor=#e53935;strokeWidth=2;" value="" vertex="1">
<mxGeometry height="200" width="380" x="60" y="310" as="geometry" />
</mxCell>
<mxCell id="16" parent="1" style="rounded=1;whiteSpace=wrap;html=1;fillColor=#e53935;strokeColor=none;arcSize=8;" value="" vertex="1">
<mxGeometry height="45" width="380" x="60" y="310" as="geometry" />
</mxCell>
<mxCell id="17" parent="1" style="text;html=1;strokeColor=none;fillColor=none;align=center;verticalAlign=middle;whiteSpace=wrap;rounded=0;fontSize=17;fontStyle=1;fontColor=#ffffff;" value="❌ equals() 方法" vertex="1">
<mxGeometry height="45" width="380" x="60" y="310" as="geometry" />
</mxCell>
<mxCell id="18" parent="1" style="rounded=1;whiteSpace=wrap;html=1;fillColor=#ffffff;strokeColor=#ef9a9a;strokeWidth=1;" value="" vertex="1">
<mxGeometry height="55" width="340" x="80" y="365" as="geometry" />
</mxCell>
<mxCell id="19" parent="1" style="text;html=1;strokeColor=none;fillColor=none;align=center;verticalAlign=middle;whiteSpace=wrap;rounded=0;fontSize=14;" value="比较 <font color="#1565c0"><b>unscaledValue</b></font> 和 <font color="#c62828"><b>scale</b></font> 都相等<br><font color="#757575" style="font-size: 12px;">精确匹配内部表示</font>" vertex="1">
<mxGeometry height="55" width="340" x="80" y="365" as="geometry" />
</mxCell>
<mxCell id="20" parent="1" style="rounded=1;whiteSpace=wrap;html=1;fillColor=#ffcdd2;strokeColor=#e53935;strokeWidth=2;" value="" vertex="1">
<mxGeometry height="65" width="340" x="80" y="430" as="geometry" />
</mxCell>
<mxCell id="21" parent="1" style="text;html=1;strokeColor=none;fillColor=none;align=center;verticalAlign=middle;whiteSpace=wrap;rounded=0;fontSize=13;" value="<font face="Courier New">new BigDecimal("1.0")<br> .equals(new BigDecimal("1.00"))</font><br><font style="font-size: 15px;">→ <b><font color="#c62828">false</font></b></font>" vertex="1">
<mxGeometry height="65" width="340" x="80" y="430" as="geometry" />
</mxCell>
<mxCell id="22" parent="1" style="rounded=1;whiteSpace=wrap;html=1;fillColor=#e8f5e9;strokeColor=#4caf50;strokeWidth=2;" value="" vertex="1">
<mxGeometry height="200" width="380" x="460" y="310" as="geometry" />
</mxCell>
<mxCell id="23" parent="1" style="rounded=1;whiteSpace=wrap;html=1;fillColor=#4caf50;strokeColor=none;arcSize=8;" value="" vertex="1">
<mxGeometry height="45" width="380" x="460" y="310" as="geometry" />
</mxCell>
<mxCell id="24" parent="1" style="text;html=1;strokeColor=none;fillColor=none;align=center;verticalAlign=middle;whiteSpace=wrap;rounded=0;fontSize=17;fontStyle=1;fontColor=#ffffff;" value="✅ compareTo() 方法" vertex="1">
<mxGeometry height="45" width="380" x="460" y="310" as="geometry" />
</mxCell>
<mxCell id="25" parent="1" style="rounded=1;whiteSpace=wrap;html=1;fillColor=#ffffff;strokeColor=#a5d6a7;strokeWidth=1;" value="" vertex="1">
<mxGeometry height="55" width="340" x="480" y="365" as="geometry" />
</mxCell>
<mxCell id="26" parent="1" style="text;html=1;strokeColor=none;fillColor=none;align=center;verticalAlign=middle;whiteSpace=wrap;rounded=0;fontSize=14;" value="只比较 <b>数学值</b>，忽略 scale<br><font color="#757575" style="font-size: 12px;">语义上的数值比较</font>" vertex="1">
<mxGeometry height="55" width="340" x="480" y="365" as="geometry" />
</mxCell>
<mxCell id="27" parent="1" style="rounded=1;whiteSpace=wrap;html=1;fillColor=#c8e6c9;strokeColor=#4caf50;strokeWidth=2;" value="" vertex="1">
<mxGeometry height="65" width="340" x="480" y="430" as="geometry" />
</mxCell>
<mxCell id="28" parent="1" style="text;html=1;strokeColor=none;fillColor=none;align=center;verticalAlign=middle;whiteSpace=wrap;rounded=0;fontSize=13;" value="<font face="Courier New">new BigDecimal("1.0")<br> .compareTo(new BigDecimal("1.00"))</font><br><font style="font-size: 15px;">→ <b><font color="#2e7d32">0</font></b> (相等)</font>" vertex="1">
<mxGeometry height="65" width="340" x="480" y="430" as="geometry" />
</mxCell>
<mxCell id="29" parent="1" style="ellipse;whiteSpace=wrap;html=1;fillColor=#7b1fa2;strokeColor=none;shadow=1;" value="" vertex="1">
<mxGeometry height="50" width="50" x="425" y="385" as="geometry" />
</mxCell>
<mxCell id="30" parent="1" style="text;html=1;strokeColor=none;fillColor=none;align=center;verticalAlign=middle;whiteSpace=wrap;rounded=0;fontSize=14;" value="<font color="#ffffff"><b>VS</b></font>" vertex="1">
<mxGeometry height="50" width="50" x="425" y="385" as="geometry" />
</mxCell>
<mxCell id="31" parent="1" style="rounded=1;whiteSpace=wrap;html=1;fillColor=#e8eaf6;strokeColor=#5c6bc0;strokeWidth=2;" value="" vertex="1">
<mxGeometry height="120" width="780" x="60" y="525" as="geometry" />
</mxCell>
<mxCell id="32" parent="1" style="rounded=0;whiteSpace=wrap;html=1;fillColor=#5c6bc0;strokeColor=none;" value="" vertex="1">
<mxGeometry height="35" width="200" x="60" y="525" as="geometry" />
</mxCell>
<mxCell id="33" parent="1" style="text;html=1;strokeColor=none;fillColor=none;align=center;verticalAlign=middle;whiteSpace=wrap;rounded=0;fontSize=14;" value="<font color="#ffffff"><b>比较场景</b></font>" vertex="1">
<mxGeometry height="35" width="200" x="60" y="525" as="geometry" />
</mxCell>
<mxCell id="34" parent="1" style="rounded=0;whiteSpace=wrap;html=1;fillColor=#e53935;strokeColor=none;" value="" vertex="1">
<mxGeometry height="35" width="290" x="260" y="525" as="geometry" />
</mxCell>
<mxCell id="35" parent="1" style="text;html=1;strokeColor=none;fillColor=none;align=center;verticalAlign=middle;whiteSpace=wrap;rounded=0;fontSize=14;" value="<font color="#ffffff"><b>equals()</b></font>" vertex="1">
<mxGeometry height="35" width="290" x="260" y="525" as="geometry" />
</mxCell>
<mxCell id="36" parent="1" style="rounded=0;whiteSpace=wrap;html=1;fillColor=#4caf50;strokeColor=none;" value="" vertex="1">
<mxGeometry height="35" width="290" x="550" y="525" as="geometry" />
</mxCell>
<mxCell id="37" parent="1" style="text;html=1;strokeColor=none;fillColor=none;align=center;verticalAlign=middle;whiteSpace=wrap;rounded=0;fontSize=14;" value="<font color="#ffffff"><b>compareTo() == 0</b></font>" vertex="1">
<mxGeometry height="35" width="290" x="550" y="525" as="geometry" />
</mxCell>
<mxCell id="38" parent="1" style="rounded=0;whiteSpace=wrap;html=1;fillColor=#ffffff;strokeColor=#c5cae9;strokeWidth=1;" value="" vertex="1">
<mxGeometry height="40" width="200" x="60" y="560" as="geometry" />
</mxCell>
<mxCell id="39" parent="1" style="text;html=1;strokeColor=none;fillColor=none;align=center;verticalAlign=middle;whiteSpace=wrap;rounded=0;fontSize=13;" value="<font face="Courier New">1.0 vs 1.00</font>" vertex="1">
<mxGeometry height="40" width="200" x="60" y="560" as="geometry" />
</mxCell>
<mxCell id="40" parent="1" style="rounded=0;whiteSpace=wrap;html=1;fillColor=#ffebee;strokeColor=#ef9a9a;strokeWidth=1;" value="" vertex="1">
<mxGeometry height="40" width="290" x="260" y="560" as="geometry" />
</mxCell>
<mxCell id="41" parent="1" style="text;html=1;strokeColor=none;fillColor=none;align=center;verticalAlign=middle;whiteSpace=wrap;rounded=0;fontSize=13;" value="<font color="#c62828"><b>false</b></font> <font color="#757575">(scale不同)</font>" vertex="1">
<mxGeometry height="40" width="290" x="260" y="560" as="geometry" />
</mxCell>
<mxCell id="42" parent="1" style="rounded=0;whiteSpace=wrap;html=1;fillColor=#e8f5e9;strokeColor=#a5d6a7;strokeWidth=1;" value="" vertex="1">
<mxGeometry height="40" width="290" x="550" y="560" as="geometry" />
</mxCell>
<mxCell id="43" parent="1" style="text;html=1;strokeColor=none;fillColor=none;align=center;verticalAlign=middle;whiteSpace=wrap;rounded=0;fontSize=13;" value="<font color="#2e7d32"><b>true</b></font> <font color="#757575">(数值相等)</font>" vertex="1">
<mxGeometry height="40" width="290" x="550" y="560" as="geometry" />
</mxCell>
<mxCell id="44" parent="1" style="rounded=0;whiteSpace=wrap;html=1;fillColor=#ffffff;strokeColor=#c5cae9;strokeWidth=1;" value="" vertex="1">
<mxGeometry height="40" width="200" x="60" y="600" as="geometry" />
</mxCell>
<mxCell id="45" parent="1" style="text;html=1;strokeColor=none;fillColor=none;align=center;verticalAlign=middle;whiteSpace=wrap;rounded=0;fontSize=13;" value="<font face="Courier New">1.0 vs 1.0</font>" vertex="1">
<mxGeometry height="40" width="200" x="60" y="600" as="geometry" />
</mxCell>
<mxCell id="46" parent="1" style="rounded=0;whiteSpace=wrap;html=1;fillColor=#e8f5e9;strokeColor=#a5d6a7;strokeWidth=1;" value="" vertex="1">
<mxGeometry height="40" width="290" x="260" y="600" as="geometry" />
</mxCell>
<mxCell id="47" parent="1" style="text;html=1;strokeColor=none;fillColor=none;align=center;verticalAlign=middle;whiteSpace=wrap;rounded=0;fontSize=13;" value="<font color="#2e7d32"><b>true</b></font> <font color="#757575">(完全相同)</font>" vertex="1">
<mxGeometry height="40" width="290" x="260" y="600" as="geometry" />
</mxCell>
<mxCell id="48" parent="1" style="rounded=0;whiteSpace=wrap;html=1;fillColor=#e8f5e9;strokeColor=#a5d6a7;strokeWidth=1;" value="" vertex="1">
<mxGeometry height="40" width="290" x="550" y="600" as="geometry" />
</mxCell>
<mxCell id="49" parent="1" style="text;html=1;strokeColor=none;fillColor=none;align=center;verticalAlign=middle;whiteSpace=wrap;rounded=0;fontSize=13;" value="<font color="#2e7d32"><b>true</b></font> <font color="#757575">(数值相等)</font>" vertex="1">
<mxGeometry height="40" width="290" x="550" y="600" as="geometry" />
</mxCell>
<mxCell id="50" parent="1" style="rounded=1;whiteSpace=wrap;html=1;fillColor=#fff8e1;strokeColor=#ffa000;strokeWidth=2;" value="" vertex="1">
<mxGeometry height="35" width="780" x="60" y="660" as="geometry" />
</mxCell>
<mxCell id="51" parent="1" style="text;html=1;strokeColor=none;fillColor=none;align=center;verticalAlign=middle;whiteSpace=wrap;rounded=0;fontSize=14;fontColor=#e65100;" value="💡 <b>最佳实践</b>：比较 BigDecimal 数值时，始终使用 <font face="Courier New" color="#2e7d32"><b>compareTo() == 0</b></font> 而非 equals()" vertex="1">
<mxGeometry height="35" width="780" x="60" y="660" as="geometry" />
</mxCell>
</root>
</mxGraphModel>
</diagram>
</mxfile>
8.5 工具类封装
import java.math.BigDecimal;
import java.math.RoundingMode;
/**
* BigDecimal 计算工具类
*/
public final class BigDecimalUtil {
// 默认精度
private static final int DEFAULT_SCALE = 2;
// 默认舍入模式
private static final RoundingMode DEFAULT_ROUNDING = RoundingMode.HALF_UP;
private BigDecimalUtil() {}
/**
* 加法
*/
public static BigDecimal add(double v1, double v2) {
BigDecimal b1 = BigDecimal.valueOf(v1);
BigDecimal b2 = BigDecimal.valueOf(v2);
return b1.add(b2);
}
/**
* 减法
*/
public static BigDecimal subtract(double v1, double v2) {
BigDecimal b1 = BigDecimal.valueOf(v1);
BigDecimal b2 = BigDecimal.valueOf(v2);
return b1.subtract(b2);
}
/**
* 乘法
*/
public static BigDecimal multiply(double v1, double v2) {
BigDecimal b1 = BigDecimal.valueOf(v1);
BigDecimal b2 = BigDecimal.valueOf(v2);
return b1.multiply(b2);
}
/**
* 除法（使用默认精度和舍入模式）
*/
public static BigDecimal divide(double v1, double v2) {
return divide(v1, v2, DEFAULT_SCALE, DEFAULT_ROUNDING);
}
/**
* 除法（指定精度和舍入模式）
*/
public static BigDecimal divide(double v1, double v2, int scale, RoundingMode mode) {
if (scale < 0) {
throw new IllegalArgumentException("精度不能为负数");
}
BigDecimal b1 = BigDecimal.valueOf(v1);
BigDecimal b2 = BigDecimal.valueOf(v2);
return b1.divide(b2, scale, mode);
}
/**
* 四舍五入
*/
public static BigDecimal round(double v, int scale) {
return BigDecimal.valueOf(v).setScale(scale, DEFAULT_ROUNDING);
}
/**
* 比较大小
* @return 正数: v1 > v2, 0: v1 == v2, 负数: v1 < v2
*/
public static int compare(double v1, double v2) {
BigDecimal b1 = BigDecimal.valueOf(v1);
BigDecimal b2 = BigDecimal.valueOf(v2);
return b1.compareTo(b2);
}
}
九、BigInteger 大整数
9.1 为什么需要 BigInteger
public class WhyBigIntegerDemo {
public static void main(String[] args) {
// long 的最大值
long maxLong = Long.MAX_VALUE; // 9223372036854775807
System.out.println("Long.MAX_VALUE = " + maxLong);
// 溢出
System.out.println("Long.MAX_VALUE + 1 = " + (maxLong + 1)); // 负数！
// BigInteger 可以表示任意大小的整数
BigInteger big = new BigInteger("9223372036854775808"); // Long.MAX_VALUE + 1
System.out.println("BigInteger = " + big);
// 更大的数
BigInteger huge = new BigInteger("123456789012345678901234567890");
System.out.println("Huge = " + huge);
}
}
9.2 BigInteger 基本用法
import java.math.BigInteger;
public class BigIntegerDemo {
public static void main(String[] args) {
// ═══════════════════════════════════════════════════════════════
// 创建 BigInteger
// ═══════════════════════════════════════════════════════════════
BigInteger a = new BigInteger("12345678901234567890");
BigInteger b = BigInteger.valueOf(100L); // 从 long 创建
BigInteger c = BigInteger.TEN; // 常量
BigInteger d = BigInteger.ZERO;
BigInteger e = BigInteger.ONE;
// ═══════════════════════════════════════════════════════════════
// 四则运算
// ═══════════════════════════════════════════════════════════════
BigInteger x = new BigInteger("1000000000000");
BigInteger y = new BigInteger("999999999999");
System.out.println("加法: " + x.add(y));
System.out.println("减法: " + x.subtract(y));
System.out.println("乘法: " + x.multiply(y));
System.out.println("除法: " + x.divide(y));
System.out.println("取余: " + x.remainder(y));
System.out.println("幂运算: " + x.pow(2));
// 同时获取商和余数
BigInteger[] divideAndRemainder = x.divideAndRemainder(y);
System.out.println("商: " + divideAndRemainder[0]);
System.out.println("余数: " + divideAndRemainder[1]);
// ═══════════════════════════════════════════════════════════════
// 位运算
// ═══════════════════════════════════════════════════════════════
BigInteger num = new BigInteger("100");
System.out.println("左移2位: " + num.shiftLeft(2)); // 400
System.out.println("右移2位: " + num.shiftRight(2)); // 25
System.out.println("按位与: " + num.and(new BigInteger("50")));
System.out.println("按位或: " + num.or(new BigInteger("50")));
// ═══════════════════════════════════════════════════════════════
// 比较
// ═══════════════════════════════════════════════════════════════
System.out.println("compareTo: " + x.compareTo(y)); // 正数表示 x > y
System.out.println("equals: " + x.equals(y));
// ═══════════════════════════════════════════════════════════════
// 类型转换
// ═══════════════════════════════════════════════════════════════
BigInteger small = new BigInteger("100");
int intValue = small.intValue(); // 转为 int（可能溢出）
long longValue = small.longValue(); // 转为 long（可能溢出）
// 安全转换（溢出时抛出 ArithmeticException）
int safeInt = small.intValueExact();
long safeLong = small.longValueExact();
}
}
9.3 BigInteger 内部原理
<mxfile>
<diagram id="biginteger-internal" name="BigInteger 内部实现">
<mxGraphModel dx="926" dy="817" grid="1" gridSize="10" guides="1" tooltips="1" connect="1" arrows="1" fold="1" page="1" pageScale="1" pageWidth="900" pageHeight="700" math="0" shadow="0">
<root>
<mxCell id="0" />
<mxCell id="1" parent="0" />
<mxCell id="2" parent="1" style="rounded=1;whiteSpace=wrap;html=1;fillColor=#fafafa;strokeColor=#1565c0;strokeWidth=3;shadow=1;" value="" vertex="1">
<mxGeometry height="700" width="820" x="40" y="20" as="geometry" />
</mxCell>
<mxCell id="3" parent="1" style="text;html=1;strokeColor=none;fillColor=none;align=center;verticalAlign=middle;whiteSpace=wrap;rounded=0;fontSize=26;fontStyle=1;fontColor=#0d47a1;" value="BigInteger 内部实现" vertex="1">
<mxGeometry height="45" width="340" x="280" y="35" as="geometry" />
</mxCell>
<mxCell id="4" parent="1" style="rounded=1;whiteSpace=wrap;html=1;fillColor=#e3f2fd;strokeColor=#1976d2;strokeWidth=2;" value="" vertex="1">
<mxGeometry height="180" width="780" x="60" y="95" as="geometry" />
</mxCell>
<mxCell id="5" parent="1" style="rounded=1;whiteSpace=wrap;html=1;fillColor=#1976d2;strokeColor=none;" value="" vertex="1">
<mxGeometry height="40" width="780" x="60" y="95" as="geometry" />
</mxCell>
<mxCell id="6" parent="1" style="text;html=1;strokeColor=none;fillColor=none;align=center;verticalAlign=middle;whiteSpace=wrap;rounded=0;fontSize=17;fontStyle=1;fontColor=#ffffff;" value="📦 BigInteger 类结构" vertex="1">
<mxGeometry height="40" width="780" x="60" y="95" as="geometry" />
</mxCell>
<mxCell id="7" parent="1" style="text;html=1;strokeColor=none;fillColor=none;align=center;verticalAlign=middle;whiteSpace=wrap;rounded=0;fontSize=14;fontColor=#424242;" value="BigInteger 内部使用 <font color="#c62828"><b>int[] 数组</b></font> 存储数值，可表示任意精度的整数" vertex="1">
<mxGeometry height="25" width="780" x="60" y="140" as="geometry" />
</mxCell>
<mxCell id="8" parent="1" style="rounded=1;whiteSpace=wrap;html=1;fillColor=#263238;strokeColor=#37474f;strokeWidth=2;shadow=1;" value="" vertex="1">
<mxGeometry height="90" width="720" x="90" y="170" as="geometry" />
</mxCell>
<mxCell id="9" parent="1" style="text;html=1;strokeColor=none;fillColor=none;align=left;verticalAlign=middle;whiteSpace=wrap;rounded=0;fontSize=13;spacingLeft=15;" value="<div style="text-align: left; line-height: 1.6;"><font face="Courier New" color="#e0e0e0"><font color="#ce93d8">public class</font> <font color="#64b5f6">BigInteger</font> <font color="#ce93d8">extends</font> Number <font color="#ce93d8">implements</font> Comparable&lt;BigInteger&gt; {<br>&nbsp;&nbsp;&nbsp;&nbsp;<font color="#ce93d8">final int</font> <font color="#ffcc80">signum</font>; <font color="#81c784">// 符号：-1, 0, 1</font><br>&nbsp;&nbsp;&nbsp;&nbsp;<font color="#ce93d8">final int[]</font> <font color="#ffcc80">mag</font>; <font color="#81c784">// 数值的绝对值（大端序）</font><br>}</font></div>" vertex="1">
<mxGeometry height="90" width="720" x="90" y="170" as="geometry" />
</mxCell>
<mxCell id="10" parent="1" style="rounded=1;whiteSpace=wrap;html=1;fillColor=#fff3e0;strokeColor=#ff9800;strokeWidth=2;" value="" vertex="1">
<mxGeometry height="120" width="380" x="60" y="290" as="geometry" />
</mxCell>
<mxCell id="11" parent="1" style="rounded=1;whiteSpace=wrap;html=1;fillColor=#ff9800;strokeColor=none;" value="" vertex="1">
<mxGeometry height="35" width="380" x="60" y="290" as="geometry" />
</mxCell>
<mxCell id="12" parent="1" style="text;html=1;strokeColor=none;fillColor=none;align=center;verticalAlign=middle;whiteSpace=wrap;rounded=0;fontSize=15;fontStyle=0;" value="<font color="#ffffff"><b>signum</b> - 符号位</font>" vertex="1">
<mxGeometry height="35" width="380" x="60" y="290" as="geometry" />
</mxCell>
<mxCell id="13" parent="1" style="rounded=0;whiteSpace=wrap;html=1;fillColor=#ffe0b2;strokeColor=#ffb74d;strokeWidth=1;" value="" vertex="1">
<mxGeometry height="30" width="100" x="80" y="335" as="geometry" />
</mxCell>
<mxCell id="14" parent="1" style="text;html=1;strokeColor=none;fillColor=none;align=center;verticalAlign=middle;whiteSpace=wrap;rounded=0;fontSize=13;" value="<font face="Courier New"><b>-1</b></font> 负数" vertex="1">
<mxGeometry height="30" width="100" x="80" y="335" as="geometry" />
</mxCell>
<mxCell id="15" parent="1" style="rounded=0;whiteSpace=wrap;html=1;fillColor=#ffe0b2;strokeColor=#ffb74d;strokeWidth=1;" value="" vertex="1">
<mxGeometry height="30" width="100" x="190" y="335" as="geometry" />
</mxCell>
<mxCell id="16" parent="1" style="text;html=1;strokeColor=none;fillColor=none;align=center;verticalAlign=middle;whiteSpace=wrap;rounded=0;fontSize=13;" value="<font face="Courier New"><b>0</b></font> 零" vertex="1">
<mxGeometry height="30" width="100" x="190" y="335" as="geometry" />
</mxCell>
<mxCell id="17" parent="1" style="rounded=0;whiteSpace=wrap;html=1;fillColor=#ffe0b2;strokeColor=#ffb74d;strokeWidth=1;" value="" vertex="1">
<mxGeometry height="30" width="120" x="300" y="335" as="geometry" />
</mxCell>
<mxCell id="18" parent="1" style="text;html=1;strokeColor=none;fillColor=none;align=center;verticalAlign=middle;whiteSpace=wrap;rounded=0;fontSize=13;" value="<font face="Courier New"><b>1</b></font> 正数" vertex="1">
<mxGeometry height="30" width="120" x="300" y="335" as="geometry" />
</mxCell>
<mxCell id="19" parent="1" style="text;html=1;strokeColor=none;fillColor=none;align=center;verticalAlign=middle;whiteSpace=wrap;rounded=0;fontSize=12;" value="<font color="#757575">仅存储符号，不参与数值计算</font>" vertex="1">
<mxGeometry height="25" width="380" x="60" y="375" as="geometry" />
</mxCell>
<mxCell id="20" parent="1" style="rounded=1;whiteSpace=wrap;html=1;fillColor=#e8f5e9;strokeColor=#4caf50;strokeWidth=2;" value="" vertex="1">
<mxGeometry height="120" width="380" x="460" y="290" as="geometry" />
</mxCell>
<mxCell id="21" parent="1" style="rounded=1;whiteSpace=wrap;html=1;fillColor=#4caf50;strokeColor=none;" value="" vertex="1">
<mxGeometry height="35" width="380" x="460" y="290" as="geometry" />
</mxCell>
<mxCell id="22" parent="1" style="text;html=1;strokeColor=none;fillColor=none;align=center;verticalAlign=middle;whiteSpace=wrap;rounded=0;fontSize=15;" value="<font color="#ffffff"><b>mag[]</b> - 数值数组</font>" vertex="1">
<mxGeometry height="35" width="380" x="460" y="290" as="geometry" />
</mxCell>
<mxCell id="23" parent="1" style="text;html=1;strokeColor=none;fillColor=none;align=left;verticalAlign=middle;whiteSpace=wrap;rounded=0;fontSize=13;spacingLeft=20;" value="<div style="text-align: left;">• 存储数值的<b>绝对值</b><br>• 采用<font color="#1565c0"><b>大端序</b></font>（高位在前）<br>• 每个 int 存储 <font color="#c62828"><b>32 位</b></font>数据<br>• 数组长度动态扩展</div>" vertex="1">
<mxGeometry height="75" width="380" x="460" y="330" as="geometry" />
</mxCell>
<mxCell id="24" parent="1" style="rounded=1;whiteSpace=wrap;html=1;fillColor=#f3e5f5;strokeColor=#9c27b0;strokeWidth=2;" value="" vertex="1">
<mxGeometry height="200" width="780" x="60" y="425" as="geometry" />
</mxCell>
<mxCell id="25" parent="1" style="rounded=1;whiteSpace=wrap;html=1;fillColor=#9c27b0;strokeColor=none;" value="" vertex="1">
<mxGeometry height="40" width="780" x="60" y="425" as="geometry" />
</mxCell>
<mxCell id="26" parent="1" style="text;html=1;strokeColor=none;fillColor=none;align=center;verticalAlign=middle;whiteSpace=wrap;rounded=0;fontSize=16;fontStyle=1;fontColor=#ffffff;" value="📝 示例：BigInteger("12345678901234567890")" vertex="1">
<mxGeometry height="40" width="780" x="60" y="425" as="geometry" />
</mxCell>
<mxCell id="27" parent="1" style="rounded=1;whiteSpace=wrap;html=1;fillColor=#ffffff;strokeColor=#ce93d8;strokeWidth=2;" value="" vertex="1">
<mxGeometry height="55" width="200" x="90" y="480" as="geometry" />
</mxCell>
<mxCell id="28" parent="1" style="text;html=1;strokeColor=none;fillColor=none;align=center;verticalAlign=middle;whiteSpace=wrap;rounded=0;fontSize=14;" value="<font face="Courier New">signum = <font color="#4caf50"><b>1</b></font></font><br><font color="#757575" style="font-size: 12px;">(正数)</font>" vertex="1">
<mxGeometry height="55" width="200" x="90" y="480" as="geometry" />
</mxCell>
<mxCell id="29" parent="1" style="rounded=1;whiteSpace=wrap;html=1;fillColor=#ffffff;strokeColor=#ce93d8;strokeWidth=2;" value="" vertex="1">
<mxGeometry height="130" width="510" x="310" y="480" as="geometry" />
</mxCell>
<mxCell id="30" parent="1" style="text;html=1;strokeColor=none;fillColor=none;align=left;verticalAlign=middle;whiteSpace=wrap;rounded=0;fontSize=14;spacingLeft=10;" value="<font face="Courier New">mag[] = </font>" vertex="1">
<mxGeometry height="30" width="100" x="310" y="485" as="geometry" />
</mxCell>
<mxCell id="31" parent="1" style="rounded=0;whiteSpace=wrap;html=1;fillColor=#e1bee7;strokeColor=#9c27b0;strokeWidth=2;" value="" vertex="1">
<mxGeometry height="70" width="150" x="330" y="530" as="geometry" />
</mxCell>
<mxCell id="32" parent="1" style="text;html=1;strokeColor=none;fillColor=none;align=center;verticalAlign=middle;whiteSpace=wrap;rounded=0;fontSize=13;" value="<font face="Courier New" color="#6a1b9a"><b>0xAB54A98C</b></font><br><font color="#757575" style="font-size: 11px;">mag[0] - 高位</font><br><font color="#9e9e9e" style="font-size: 10px;">32 bits</font>" vertex="1">
<mxGeometry height="70" width="150" x="330" y="530" as="geometry" />
</mxCell>
<mxCell id="33" parent="1" style="rounded=0;whiteSpace=wrap;html=1;fillColor=#e1bee7;strokeColor=#9c27b0;strokeWidth=2;" value="" vertex="1">
<mxGeometry height="70" width="150" x="490" y="530" as="geometry" />
</mxCell>
<mxCell id="34" parent="1" style="text;html=1;strokeColor=none;fillColor=none;align=center;verticalAlign=middle;whiteSpace=wrap;rounded=0;fontSize=13;" value="<font face="Courier New" color="#6a1b9a"><b>0xEB1F0AD2</b></font><br><font color="#757575" style="font-size: 11px;">mag[1] - 低位</font><br><font color="#9e9e9e" style="font-size: 10px;">32 bits</font>" vertex="1">
<mxGeometry height="70" width="150" x="490" y="530" as="geometry" />
</mxCell>
<mxCell id="35" parent="1" style="rounded=0;whiteSpace=wrap;html=1;fillColor=#f3e5f5;strokeColor=#ce93d8;strokeWidth=1;strokeDasharray=3 3;" value="" vertex="1">
<mxGeometry height="70" width="60" x="650" y="530" as="geometry" />
</mxCell>
<mxCell id="36" parent="1" style="text;html=1;strokeColor=none;fillColor=none;align=center;verticalAlign=middle;whiteSpace=wrap;rounded=0;fontSize=18;" value="<font color="#9e9e9e">...</font>" vertex="1">
<mxGeometry height="70" width="60" x="644" y="530" as="geometry" />
</mxCell>
<mxCell id="37" edge="1" parent="1" style="endArrow=classic;html=1;strokeColor=#9c27b0;strokeWidth=2;" value="">
<mxGeometry height="50" relative="1" width="50" as="geometry">
<mxPoint x="410" y="510" as="sourcePoint" />
<mxPoint x="570" y="510" as="targetPoint" />
</mxGeometry>
</mxCell>
<mxCell id="38" parent="1" style="text;html=1;strokeColor=none;fillColor=none;align=center;verticalAlign=middle;whiteSpace=wrap;rounded=0;fontSize=11;" value="<font color="#9c27b0" style="font-size: 11px;">大端序</font>" vertex="1">
<mxGeometry height="20" width="60" x="460" y="490" as="geometry" />
</mxCell>
<mxCell id="39" parent="1" style="rounded=1;whiteSpace=wrap;html=1;fillColor=#ede7f6;strokeColor=#7e57c2;strokeWidth=1;" value="" vertex="1">
<mxGeometry height="70" width="100" x="715" y="530" as="geometry" />
</mxCell>
<mxCell id="40" parent="1" style="text;html=1;strokeColor=none;fillColor=none;align=center;verticalAlign=middle;whiteSpace=wrap;rounded=0;fontSize=12;fontColor=#5e35b1;" value="<font style="font-size: 11px;">多个 int<br>组合表示<br><b>任意大整数</b></font>" vertex="1">
<mxGeometry height="70" width="100" x="715" y="530" as="geometry" />
</mxCell>
<mxCell id="41" parent="1" style="rounded=1;whiteSpace=wrap;html=1;fillColor=#fff8e1;strokeColor=#ffa000;strokeWidth=2;" value="" vertex="1">
<mxGeometry height="35" width="780" x="60" y="640" as="geometry" />
</mxCell>
<mxCell id="42" parent="1" style="text;html=1;strokeColor=none;fillColor=none;align=center;verticalAlign=middle;whiteSpace=wrap;rounded=0;fontSize=14;fontColor=#e65100;" value="⚠️ <b>注意</b>：BigInteger 是<font color="#c62828"><b>不可变对象</b></font>，每次运算（add、multiply等）都会创建新对象，注意性能开销" vertex="1">
<mxGeometry height="35" width="780" x="60" y="640" as="geometry" />
</mxCell>
</root>
</mxGraphModel>
</diagram>
</mxfile>
十、总结
<mxfile>
<diagram id="data-types-overview" name="数据类型详解">
<mxGraphModel dx="900" dy="780" grid="1" gridSize="10" guides="1" tooltips="1" connect="1" arrows="1" fold="1" page="1" pageScale="1" pageWidth="900" pageHeight="780">
<root>
<mxCell id="0" />
<mxCell id="1" parent="0" />
<mxCell id="2" value="数据类型详解 - 核心要点" style="text;html=1;strokeColor=none;fillColor=none;align=center;verticalAlign=middle;fontSize=26;fontStyle=1;fontColor=#1E293B;" vertex="1" parent="1">
<mxGeometry x="225" y="15" width="450" height="40" as="geometry" />
</mxCell>
<mxCell id="3" value="Java 数据类型知识体系速览" style="text;html=1;strokeColor=none;fillColor=#6366F1;align=center;verticalAlign=middle;fontSize=12;fontColor=#FFFFFF;rounded=1;" vertex="1" parent="1">
<mxGeometry x="325" y="55" width="250" height="24" as="geometry" />
</mxCell>
<mxCell id="4" value="" style="rounded=1;whiteSpace=wrap;html=1;fillColor=#EFF6FF;strokeColor=#3B82F6;strokeWidth=3;" vertex="1" parent="1">
<mxGeometry x="40" y="95" width="400" height="165" as="geometry" />
</mxCell>
<mxCell id="5" value="📊 基本类型" style="text;html=1;strokeColor=none;fillColor=#3B82F6;align=center;verticalAlign=middle;fontSize=15;fontStyle=1;fontColor=#FFFFFF;rounded=1;" vertex="1" parent="1">
<mxGeometry x="55" y="108" width="120" height="30" as="geometry" />
</mxCell>
<mxCell id="6" value="Primitive Types" style="text;html=1;strokeColor=none;fillColor=none;align=left;verticalAlign=middle;fontSize=11;fontColor=#3B82F6;fontStyle=2;" vertex="1" parent="1">
<mxGeometry x="180" y="112" width="100" height="22" as="geometry" />
</mxCell>
<mxCell id="7" value="" style="rounded=1;whiteSpace=wrap;html=1;fillColor=#FFFFFF;strokeColor=#BFDBFE;strokeWidth=1;" vertex="1" parent="1">
<mxGeometry x="55" y="145" width="370" height="100" as="geometry" />
</mxCell>
<mxCell id="8" value="8 种" style="text;html=1;strokeColor=none;fillColor=#3B82F6;align=center;verticalAlign=middle;fontSize=11;fontStyle=1;fontColor=#FFFFFF;rounded=1;" vertex="1" parent="1">
<mxGeometry x="65" y="152" width="40" height="20" as="geometry" />
</mxCell>
<mxCell id="9" value="byte / short / int / long / float / double / char / boolean" style="text;html=1;strokeColor=none;fillColor=#DBEAFE;align=left;verticalAlign=middle;fontSize=11;fontFamily=Courier New;fontColor=#1E40AF;rounded=1;spacingLeft=6;" vertex="1" parent="1">
<mxGeometry x="110" y="150" width="305" height="24" as="geometry" />
</mxCell>
<mxCell id="10" value="特点" style="text;html=1;strokeColor=none;fillColor=#3B82F6;align=center;verticalAlign=middle;fontSize=11;fontStyle=1;fontColor=#FFFFFF;rounded=1;" vertex="1" parent="1">
<mxGeometry x="65" y="180" width="40" height="20" as="geometry" />
</mxCell>
<mxCell id="11" value="直接存储数值，效率高，存储在栈(局部)或堆(成员)中" style="text;html=1;strokeColor=none;fillColor=none;align=left;verticalAlign=middle;fontSize=12;fontColor=#1E40AF;spacingLeft=6;" vertex="1" parent="1">
<mxGeometry x="110" y="178" width="305" height="24" as="geometry" />
</mxCell>
<mxCell id="12" value="默认值" style="text;html=1;strokeColor=none;fillColor=#3B82F6;align=center;verticalAlign=middle;fontSize=11;fontStyle=1;fontColor=#FFFFFF;rounded=1;" vertex="1" parent="1">
<mxGeometry x="65" y="208" width="50" height="20" as="geometry" />
</mxCell>
<mxCell id="13" value="0" style="text;html=1;strokeColor=none;fillColor=#DBEAFE;align=center;verticalAlign=middle;fontSize=11;fontFamily=Courier New;fontStyle=1;fontColor=#1E40AF;rounded=1;" vertex="1" parent="1">
<mxGeometry x="125" y="208" width="40" height="20" as="geometry" />
</mxCell>
<mxCell id="14" value="0.0" style="text;html=1;strokeColor=none;fillColor=#DBEAFE;align=center;verticalAlign=middle;fontSize=11;fontFamily=Courier New;fontStyle=1;fontColor=#1E40AF;rounded=1;" vertex="1" parent="1">
<mxGeometry x="175" y="208" width="40" height="20" as="geometry" />
</mxCell>
<mxCell id="15" value="false" style="text;html=1;strokeColor=none;fillColor=#DBEAFE;align=center;verticalAlign=middle;fontSize=11;fontFamily=Courier New;fontStyle=1;fontColor=#1E40AF;rounded=1;" vertex="1" parent="1">
<mxGeometry x="225" y="208" width="45" height="20" as="geometry" />
</mxCell>
<mxCell id="16" value="\u0000" style="text;html=1;strokeColor=none;fillColor=#DBEAFE;align=center;verticalAlign=middle;fontSize=11;fontFamily=Courier New;fontStyle=1;fontColor=#1E40AF;rounded=1;" vertex="1" parent="1">
<mxGeometry x="280" y="208" width="55" height="20" as="geometry" />
</mxCell>
<mxCell id="17" value="" style="rounded=1;whiteSpace=wrap;html=1;fillColor=#F0FDF4;strokeColor=#22C55E;strokeWidth=3;" vertex="1" parent="1">
<mxGeometry x="460" y="95" width="400" height="165" as="geometry" />
</mxCell>
<mxCell id="18" value="📦 包装类型" style="text;html=1;strokeColor=none;fillColor=#22C55E;align=center;verticalAlign=middle;fontSize=15;fontStyle=1;fontColor=#FFFFFF;rounded=1;" vertex="1" parent="1">
<mxGeometry x="475" y="108" width="120" height="30" as="geometry" />
</mxCell>
<mxCell id="19" value="Wrapper Classes" style="text;html=1;strokeColor=none;fillColor=none;align=left;verticalAlign=middle;fontSize=11;fontColor=#22C55E;fontStyle=2;" vertex="1" parent="1">
<mxGeometry x="600" y="112" width="110" height="22" as="geometry" />
</mxCell>
<mxCell id="20" value="" style="rounded=1;whiteSpace=wrap;html=1;fillColor=#FFFFFF;strokeColor=#BBF7D0;strokeWidth=1;" vertex="1" parent="1">
<mxGeometry x="475" y="145" width="370" height="100" as="geometry" />
</mxCell>
<mxCell id="21" value="用途" style="text;html=1;strokeColor=none;fillColor=#22C55E;align=center;verticalAlign=middle;fontSize=11;fontStyle=1;fontColor=#FFFFFF;rounded=1;" vertex="1" parent="1">
<mxGeometry x="485" y="152" width="40" height="20" as="geometry" />
</mxCell>
<mxCell id="22" value="泛型、集合 (List<Integer>)、可为 null 的场景" style="text;html=1;strokeColor=none;fillColor=none;align=left;verticalAlign=middle;fontSize=12;fontColor=#166534;spacingLeft=6;" vertex="1" parent="1">
<mxGeometry x="530" y="150" width="305" height="24" as="geometry" />
</mxCell>
<mxCell id="23" value="机制" style="text;html=1;strokeColor=none;fillColor=#22C55E;align=center;verticalAlign=middle;fontSize=11;fontStyle=1;fontColor=#FFFFFF;rounded=1;" vertex="1" parent="1">
<mxGeometry x="485" y="180" width="40" height="20" as="geometry" />
</mxCell>
<mxCell id="24" value="自动装箱 (valueOf) / 自动拆箱 (intValue)" style="text;html=1;strokeColor=none;fillColor=none;align=left;verticalAlign=middle;fontSize=12;fontColor=#166534;spacingLeft=6;" vertex="1" parent="1">
<mxGeometry x="530" y="178" width="305" height="24" as="geometry" />
</mxCell>
<mxCell id="25" value="缓存" style="text;html=1;strokeColor=none;fillColor=#22C55E;align=center;verticalAlign=middle;fontSize=11;fontStyle=1;fontColor=#FFFFFF;rounded=1;" vertex="1" parent="1">
<mxGeometry x="485" y="208" width="40" height="20" as="geometry" />
</mxCell>
<mxCell id="26" value="Integer 默认缓存" style="text;html=1;strokeColor=none;fillColor=none;align=left;verticalAlign=middle;fontSize=12;fontColor=#166534;spacingLeft=6;" vertex="1" parent="1">
<mxGeometry x="530" y="206" width="115" height="24" as="geometry" />
</mxCell>
<mxCell id="27" value="[-128, 127]" style="text;html=1;strokeColor=none;fillColor=#DCFCE7;align=center;verticalAlign=middle;fontSize=11;fontFamily=Courier New;fontStyle=1;fontColor=#166534;rounded=1;" vertex="1" parent="1">
<mxGeometry x="645" y="208" width="80" height="20" as="geometry" />
</mxCell>
<mxCell id="28" value="此范围 == 有效" style="text;html=1;strokeColor=none;fillColor=none;align=left;verticalAlign=middle;fontSize=11;fontColor=#166534;" vertex="1" parent="1">
<mxGeometry x="730" y="206" width="100" height="24" as="geometry" />
</mxCell>
<mxCell id="29" value="" style="rounded=1;whiteSpace=wrap;html=1;fillColor=#FEF2F2;strokeColor=#EF4444;strokeWidth=3;" vertex="1" parent="1">
<mxGeometry x="40" y="280" width="400" height="175" as="geometry" />
</mxCell>
<mxCell id="30" value="⚠️ 重点避坑" style="text;html=1;strokeColor=none;fillColor=#EF4444;align=center;verticalAlign=middle;fontSize=15;fontStyle=1;fontColor=#FFFFFF;rounded=1;" vertex="1" parent="1">
<mxGeometry x="55" y="293" width="120" height="30" as="geometry" />
</mxCell>
<mxCell id="31" value="Pitfalls" style="text;html=1;strokeColor=none;fillColor=none;align=left;verticalAlign=middle;fontSize=11;fontColor=#EF4444;fontStyle=2;" vertex="1" parent="1">
<mxGeometry x="180" y="297" width="60" height="22" as="geometry" />
</mxCell>
<mxCell id="32" value="" style="rounded=1;whiteSpace=wrap;html=1;fillColor=#FFFFFF;strokeColor=#FECACA;strokeWidth=1;" vertex="1" parent="1">
<mxGeometry x="55" y="330" width="370" height="110" as="geometry" />
</mxCell>
<mxCell id="33" value="比较陷阱" style="text;html=1;strokeColor=none;fillColor=#EF4444;align=center;verticalAlign=middle;fontSize=11;fontStyle=1;fontColor=#FFFFFF;rounded=1;" vertex="1" parent="1">
<mxGeometry x="65" y="340" width="65" height="20" as="geometry" />
</mxCell>
<mxCell id="34" value="包装类比较永远用 equals()，严禁依赖 ==" style="text;html=1;strokeColor=none;fillColor=none;align=left;verticalAlign=middle;fontSize=12;fontColor=#991B1B;spacingLeft=6;" vertex="1" parent="1">
<mxGeometry x="135" y="338" width="280" height="24" as="geometry" />
</mxCell>
<mxCell id="35" value="性能陷阱" style="text;html=1;strokeColor=none;fillColor=#EF4444;align=center;verticalAlign=middle;fontSize=11;fontStyle=1;fontColor=#FFFFFF;rounded=1;" vertex="1" parent="1">
<mxGeometry x="65" y="370" width="65" height="20" as="geometry" />
</mxCell>
<mxCell id="36" value="避免在循环中频繁拆装箱" style="text;html=1;strokeColor=none;fillColor=none;align=left;verticalAlign=middle;fontSize=12;fontColor=#991B1B;spacingLeft=6;" vertex="1" parent="1">
<mxGeometry x="135" y="368" width="160" height="24" as="geometry" />
</mxCell>
<mxCell id="37" value="sum += i" style="text;html=1;strokeColor=none;fillColor=#FEE2E2;align=center;verticalAlign=middle;fontSize=11;fontFamily=Courier New;fontStyle=1;fontColor=#991B1B;rounded=1;" vertex="1" parent="1">
<mxGeometry x="300" y="370" width="70" height="20" as="geometry" />
</mxCell>
<mxCell id="38" value="精度陷阱" style="text;html=1;strokeColor=none;fillColor=#EF4444;align=center;verticalAlign=middle;fontSize=11;fontStyle=1;fontColor=#FFFFFF;rounded=1;" vertex="1" parent="1">
<mxGeometry x="65" y="400" width="65" height="20" as="geometry" />
</mxCell>
<mxCell id="39" value="浮点数运算会丢失精度" style="text;html=1;strokeColor=none;fillColor=none;align=left;verticalAlign=middle;fontSize=12;fontColor=#991B1B;spacingLeft=6;" vertex="1" parent="1">
<mxGeometry x="135" y="398" width="150" height="24" as="geometry" />
</mxCell>
<mxCell id="40" value="0.1 + 0.2 ≠ 0.3" style="text;html=1;strokeColor=none;fillColor=#FEE2E2;align=center;verticalAlign=middle;fontSize=11;fontFamily=Courier New;fontStyle=1;fontColor=#991B1B;rounded=1;" vertex="1" parent="1">
<mxGeometry x="290" y="400" width="100" height="20" as="geometry" />
</mxCell>
<mxCell id="41" value="" style="rounded=1;whiteSpace=wrap;html=1;fillColor=#FAF5FF;strokeColor=#8B5CF6;strokeWidth=3;" vertex="1" parent="1">
<mxGeometry x="460" y="280" width="400" height="175" as="geometry" />
</mxCell>
<mxCell id="42" value="🧮 特殊处理" style="text;html=1;strokeColor=none;fillColor=#8B5CF6;align=center;verticalAlign=middle;fontSize=15;fontStyle=1;fontColor=#FFFFFF;rounded=1;" vertex="1" parent="1">
<mxGeometry x="475" y="293" width="120" height="30" as="geometry" />
</mxCell>
<mxCell id="43" value="Advanced" style="text;html=1;strokeColor=none;fillColor=none;align=left;verticalAlign=middle;fontSize=11;fontColor=#8B5CF6;fontStyle=2;" vertex="1" parent="1">
<mxGeometry x="600" y="297" width="70" height="22" as="geometry" />
</mxCell>
<mxCell id="44" value="" style="rounded=1;whiteSpace=wrap;html=1;fillColor=#FFFFFF;strokeColor=#E9D5FF;strokeWidth=1;" vertex="1" parent="1">
<mxGeometry x="475" y="330" width="370" height="110" as="geometry" />
</mxCell>
<mxCell id="45" value="金额计算" style="text;html=1;strokeColor=none;fillColor=#8B5CF6;align=center;verticalAlign=middle;fontSize=11;fontStyle=1;fontColor=#FFFFFF;rounded=1;" vertex="1" parent="1">
<mxGeometry x="485" y="340" width="65" height="20" as="geometry" />
</mxCell>
<mxCell id="46" value="必须使用 BigDecimal（构造参数传 String）" style="text;html=1;strokeColor=none;fillColor=none;align=left;verticalAlign=middle;fontSize=12;fontColor=#6D28D9;spacingLeft=6;" vertex="1" parent="1">
<mxGeometry x="555" y="338" width="280" height="24" as="geometry" />
</mxCell>
<mxCell id="47" value="超大整数" style="text;html=1;strokeColor=none;fillColor=#8B5CF6;align=center;verticalAlign=middle;fontSize=11;fontStyle=1;fontColor=#FFFFFF;rounded=1;" vertex="1" parent="1">
<mxGeometry x="485" y="370" width="65" height="20" as="geometry" />
</mxCell>
<mxCell id="48" value="超出 long 范围使用 BigInteger" style="text;html=1;strokeColor=none;fillColor=none;align=left;verticalAlign=middle;fontSize=12;fontColor=#6D28D9;spacingLeft=6;" vertex="1" parent="1">
<mxGeometry x="555" y="368" width="220" height="24" as="geometry" />
</mxCell>
<mxCell id="49" value="溢出处理" style="text;html=1;strokeColor=none;fillColor=#8B5CF6;align=center;verticalAlign=middle;fontSize=11;fontStyle=1;fontColor=#FFFFFF;rounded=1;" vertex="1" parent="1">
<mxGeometry x="485" y="400" width="65" height="20" as="geometry" />
</mxCell>
<mxCell id="50" value="注意最大值限制" style="text;html=1;strokeColor=none;fillColor=none;align=left;verticalAlign=middle;fontSize=12;fontColor=#6D28D9;spacingLeft=6;" vertex="1" parent="1">
<mxGeometry x="555" y="398" width="110" height="24" as="geometry" />
</mxCell>
<mxCell id="51" value="int 21亿" style="text;html=1;strokeColor=none;fillColor=#F3E8FF;align=center;verticalAlign=middle;fontSize=10;fontStyle=1;fontColor=#6D28D9;rounded=1;" vertex="1" parent="1">
<mxGeometry x="670" y="400" width="60" height="20" as="geometry" />
</mxCell>
<mxCell id="52" value="long 19位" style="text;html=1;strokeColor=none;fillColor=#F3E8FF;align=center;verticalAlign=middle;fontSize=10;fontStyle=1;fontColor=#6D28D9;rounded=1;" vertex="1" parent="1">
<mxGeometry x="740" y="400" width="70" height="20" as="geometry" />
</mxCell>
<mxCell id="53" value="" style="rounded=1;whiteSpace=wrap;html=1;fillColor=#FFFBEB;strokeColor=#F59E0B;strokeWidth=2;" vertex="1" parent="1">
<mxGeometry x="40" y="475" width="820" height="130" as="geometry" />
</mxCell>
<mxCell id="54" value="📋 快速选择指南" style="text;html=1;strokeColor=none;fillColor=#F59E0B;align=center;verticalAlign=middle;fontSize=14;fontStyle=1;fontColor=#FFFFFF;rounded=1;" vertex="1" parent="1">
<mxGeometry x="60" y="490" width="140" height="28" as="geometry" />
</mxCell>
<mxCell id="55" value="" style="rounded=1;whiteSpace=wrap;html=1;fillColor=#FFFFFF;strokeColor=#FDE68A;strokeWidth=1;" vertex="1" parent="1">
<mxGeometry x="55" y="530" width="180" height="60" as="geometry" />
</mxCell>
<mxCell id="56" value="局部变量 / 循环" style="text;html=1;strokeColor=none;fillColor=#FEF3C7;align=center;verticalAlign=middle;fontSize=11;fontStyle=1;fontColor=#92400E;rounded=1;" vertex="1" parent="1">
<mxGeometry x="65" y="538" width="100" height="20" as="geometry" />
</mxCell>
<mxCell id="57" value="→ 基本类型" style="text;html=1;strokeColor=none;fillColor=#3B82F6;align=center;verticalAlign=middle;fontSize=11;fontStyle=1;fontColor=#FFFFFF;rounded=1;" vertex="1" parent="1">
<mxGeometry x="65" y="563" width="80" height="20" as="geometry" />
</mxCell>
<mxCell id="58" value="" style="rounded=1;whiteSpace=wrap;html=1;fillColor=#FFFFFF;strokeColor=#FDE68A;strokeWidth=1;" vertex="1" parent="1">
<mxGeometry x="250" y="530" width="180" height="60" as="geometry" />
</mxCell>
<mxCell id="59" value="集合 / 泛型 / 可空" style="text;html=1;strokeColor=none;fillColor=#FEF3C7;align=center;verticalAlign=middle;fontSize=11;fontStyle=1;fontColor=#92400E;rounded=1;" vertex="1" parent="1">
<mxGeometry x="260" y="538" width="110" height="20" as="geometry" />
</mxCell>
<mxCell id="60" value="→ 包装类型" style="text;html=1;strokeColor=none;fillColor=#22C55E;align=center;verticalAlign=middle;fontSize=11;fontStyle=1;fontColor=#FFFFFF;rounded=1;" vertex="1" parent="1">
<mxGeometry x="260" y="563" width="80" height="20" as="geometry" />
</mxCell>
<mxCell id="61" value="" style="rounded=1;whiteSpace=wrap;html=1;fillColor=#FFFFFF;strokeColor=#FDE68A;strokeWidth=1;" vertex="1" parent="1">
<mxGeometry x="445" y="530" width="180" height="60" as="geometry" />
</mxCell>
<mxCell id="62" value="金额 / 精确计算" style="text;html=1;strokeColor=none;fillColor=#FEF3C7;align=center;verticalAlign=middle;fontSize=11;fontStyle=1;fontColor=#92400E;rounded=1;" vertex="1" parent="1">
<mxGeometry x="455" y="538" width="100" height="20" as="geometry" />
</mxCell>
<mxCell id="63" value="→ BigDecimal" style="text;html=1;strokeColor=none;fillColor=#8B5CF6;align=center;verticalAlign=middle;fontSize=11;fontStyle=1;fontColor=#FFFFFF;rounded=1;" vertex="1" parent="1">
<mxGeometry x="455" y="563" width="95" height="20" as="geometry" />
</mxCell>
<mxCell id="64" value="" style="rounded=1;whiteSpace=wrap;html=1;fillColor=#FFFFFF;strokeColor=#FDE68A;strokeWidth=1;" vertex="1" parent="1">
<mxGeometry x="640" y="530" width="205" height="60" as="geometry" />
</mxCell>
<mxCell id="65" value="超大数 / 密码学" style="text;html=1;strokeColor=none;fillColor=#FEF3C7;align=center;verticalAlign=middle;fontSize=11;fontStyle=1;fontColor=#92400E;rounded=1;" vertex="1" parent="1">
<mxGeometry x="650" y="538" width="100" height="20" as="geometry" />
</mxCell>
<mxCell id="66" value="→ BigInteger" style="text;html=1;strokeColor=none;fillColor=#EF4444;align=center;verticalAlign=middle;fontSize=11;fontStyle=1;fontColor=#FFFFFF;rounded=1;" vertex="1" parent="1">
<mxGeometry x="650" y="563" width="90" height="20" as="geometry" />
</mxCell>
<mxCell id="67" value="" style="rounded=1;whiteSpace=wrap;html=1;fillColor=#F0FDF4;strokeColor=#22C55E;strokeWidth=2;" vertex="1" parent="1">
<mxGeometry x="40" y="625" width="820" height="70" as="geometry" />
</mxCell>
<mxCell id="68" value="💡 核心原则" style="text;html=1;strokeColor=none;fillColor=#22C55E;align=center;verticalAlign=middle;fontSize=13;fontStyle=1;fontColor=#FFFFFF;rounded=1;" vertex="1" parent="1">
<mxGeometry x="60" y="640" width="100" height="26" as="geometry" />
</mxCell>
<mxCell id="69" value="能用基本类型就用基本类型（性能好）" style="text;html=1;strokeColor=none;fillColor=#DCFCE7;align=center;verticalAlign=middle;fontSize=12;fontStyle=1;fontColor=#166534;rounded=1;" vertex="1" parent="1">
<mxGeometry x="175" y="642" width="250" height="24" as="geometry" />
</mxCell>
<mxCell id="70" value="包装类比较用 equals()" style="text;html=1;strokeColor=none;fillColor=#DCFCE7;align=center;verticalAlign=middle;fontSize=12;fontStyle=1;fontColor=#166534;rounded=1;" vertex="1" parent="1">
<mxGeometry x="440" y="642" width="160" height="24" as="geometry" />
</mxCell>
<mxCell id="71" value="金额用 BigDecimal" style="text;html=1;strokeColor=none;fillColor=#DCFCE7;align=center;verticalAlign=middle;fontSize=12;fontStyle=1;fontColor=#166534;rounded=1;" vertex="1" parent="1">
<mxGeometry x="615" y="642" width="140" height="24" as="geometry" />
</mxCell>
<mxCell id="72" value="POJO 属性用包装类型（阿里规范）" style="text;html=1;strokeColor=none;fillColor=#FEF3C7;align=center;verticalAlign=middle;fontSize=11;fontColor=#92400E;rounded=1;" vertex="1" parent="1">
<mxGeometry x="280" y="670" width="220" height="20" as="geometry" />
</mxCell>
<mxCell id="73" value="避免循环中装箱" style="text;html=1;strokeColor=none;fillColor=#FEF3C7;align=center;verticalAlign=middle;fontSize=11;fontColor=#92400E;rounded=1;" vertex="1" parent="1">
<mxGeometry x="515" y="670" width="110" height="20" as="geometry" />
</mxCell>
</root>
</mxGraphModel>
</diagram>
</mxfile>
💬 评论