用javap查看编译版本

我们可以用javap命令查看class文件的编译版本。<wbr style="line-height:25px"><div style="line-height:25px">比如对Worke.class使用javap命令：javap -verbose Worker</div> <div style="line-height:25px">我将看到Worker的反编译结果。其中前几行如下：</div> <div style="line-height:25px"> <div style="line-height:25px"><span style="color:#3366FF; line-height:25px">Compiled from "Worker.java"</span></div> <div style="line-height:25px"><span style="color:#3366FF; line-height:25px">public class com.teleca.robin.Worker extends java.lang.Thread</span></div> <div style="line-height:25px"><span style="color:#3366FF; line-height:25px">SourceFile: "Worker.java"</span></div> <div style="line-height:25px"> <span style="color:#993300; line-height:25px">minor version: 0</span> </div> <div style="line-height:25px"> <span style="color:#993300; line-height:25px">major version: 49</span> </div> <div style="line-height:25px"> <span style="color:#3366FF; line-height:25px">Constant pool:</span> </div> </div> <div style="line-height:25px"> <span style="color:#003366; line-height:25px">上面的</span><span style="line-height:25px; color:rgb(153,51,0)">minor version: 0和</span><span style="line-height:25px; color:rgb(153,51,0)">major version: 49</span><span style="color:#003366; line-height:25px">就是编译</span>Worke.class<span style="color:#003366; line-height:25px">时使用的jdk编译版本号。</span> </div> <div style="line-height:25px">但是它并不是我们所熟悉的jdk版本号（比如jdk1.5）。</div> <div style="line-height:25px">不过我们可以把<span style="line-height:21px; font-family:verdana,sans-serif">从 JDK 1.1 到 JDK 1.7 编译器编译出的 class 的默认 minor.major version 汇总下就知道对应关系了。</span> </div> <div style="line-height:25px"> <span style="line-height:21px; font-family:verdana,sans-serif"></span> <table width="700" align="center" border="1" style="line-height:25px; border-collapse:collapse"><tbody style="line-height:25px"> <tr style="line-height:25px"> <td width="20%" style="line-height:25px"><span style="line-height:25px">JDK 编译器版本</span></td> <td width="30%" style="line-height:25px"><span style="line-height:25px">target 参数</span></td> <td width="25%" style="line-height:25px"><span style="line-height:25px">十六进制 minor.major</span></td> <td width="25%" style="line-height:25px"><span style="line-height:25px">十进制 minor.major</span></td> </tr> <tr style="line-height:25px"> <td style="line-height:25px"><span style="color:#003366; line-height:25px">jdk1.1.8</span></td> <td style="line-height:25px"><span style="color:#003366; line-height:25px">不能带 target 参数</span></td> <td style="line-height:25px"><span style="color:#003366; line-height:25px">00 03 00 2D</span></td> <td style="line-height:25px"><span style="color:#003366; line-height:25px">45.3</span></td> </tr> <tr style="line-height:25px"> <td style="line-height:25px"><span style="color:#003366; line-height:25px">jdk1.2.2</span></td> <td style="line-height:25px"><span style="color:#003366; line-height:25px">不带(默认为 -target 1.1)</span></td> <td style="line-height:25px"><span style="color:#003366; line-height:25px">00 03 00 2D</span></td> <td style="line-height:25px"><span style="color:#003366; line-height:25px">45.3</span></td> </tr> <tr style="line-height:25px"> <td style="line-height:25px"><span style="color:#003366; line-height:25px">jdk1.2.2</span></td> <td style="line-height:25px"><span style="color:#003366; line-height:25px">-target 1.2</span></td> <td style="line-height:25px"><span style="color:#003366; line-height:25px">00 00 00 2E</span></td> <td style="line-height:25px"><span style="color:#003366; line-height:25px">46.0</span></td> </tr> <tr style="line-height:25px"> <td style="line-height:25px"><span style="color:#003366; line-height:25px">jdk1.3.1_19</span></td> <td style="line-height:25px"><span style="color:#003366; line-height:25px">不带(默认为 -target 1.1)</span></td> <td style="line-height:25px"><span style="color:#003366; line-height:25px">00 03 00 2D</span></td> <td style="line-height:25px"><span style="color:#003366; line-height:25px">45.3</span></td> </tr> <tr style="line-height:25px"> <td style="line-height:25px"><span style="color:#003366; line-height:25px">jdk1.3.1_19</span></td> <td style="line-height:25px"><span style="color:#003366; line-height:25px">-target 1.3</span></td> <td style="line-height:25px"><span style="color:#003366; line-height:25px">00 00 00 2F</span></td> <td style="line-height:25px"><span style="color:#003366; line-height:25px">47.0</span></td> </tr> <tr style="line-height:25px"> <td style="line-height:25px"><span style="color:#003366; line-height:25px">j2sdk1.4.2_10</span></td> <td style="line-height:25px"><span style="color:#003366; line-height:25px">不带(默认为 -target 1.2)</span></td> <td style="line-height:25px"><span style="color:#003366; line-height:25px">00 00 00 2E</span></td> <td style="line-height:25px"><span style="color:#003366; line-height:25px">46.0</span></td> </tr> <tr style="line-height:25px"> <td style="line-height:25px"><span style="color:#003366; line-height:25px">j2sdk1.4.2_10</span></td> <td style="line-height:25px"><span style="color:#003366; line-height:25px">-target 1.4</span></td> <td style="line-height:25px"><span style="color:#003366; line-height:25px">00 00 00 30</span></td> <td style="line-height:25px"><span style="color:#003366; line-height:25px">48.0</span></td> </tr> <tr style="line-height:25px"> <td style="line-height:25px"><span style="color:#003366; line-height:25px">jdk1.5.0_11</span></td> <td style="line-height:25px"><span style="color:#003366; line-height:25px">不带(默认为 -target 1.5)</span></td> <td style="line-height:25px"><span style="color:#003366; line-height:25px">00 00 00 31</span></td> <td style="line-height:25px"><span style="color:#003366; line-height:25px">49.0</span></td> </tr> <tr style="line-height:25px"> <td style="line-height:25px"><span style="color:#003366; line-height:25px">jdk1.5.0_11</span></td> <td style="line-height:25px"><span style="color:#003366; line-height:25px">-target 1.4 -source 1.4</span></td> <td style="line-height:25px"><span style="color:#003366; line-height:25px">00 00 00 30</span></td> <td style="line-height:25px"><span style="color:#003366; line-height:25px">48.0</span></td> </tr> <tr style="line-height:25px"> <td style="line-height:25px"><span style="color:#003366; line-height:25px">jdk1.6.0_01</span></td> <td style="line-height:25px"><span style="color:#003366; line-height:25px">不带(默认为 -target 1.6)</span></td> <td style="line-height:25px"><span style="color:#003366; line-height:25px">00 00 00 32</span></td> <td style="line-height:25px"><span style="color:#003366; line-height:25px">50.0</span></td> </tr> <tr style="line-height:25px"> <td style="line-height:25px"><span style="color:#003366; line-height:25px">jdk1.6.0_01</span></td> <td style="line-height:25px"><span style="color:#003366; line-height:25px">-target 1.5</span></td> <td style="line-height:25px"><span style="color:#003366; line-height:25px">00 00 00 31</span></td> <td style="line-height:25px"><span style="color:#003366; line-height:25px">49.0</span></td> </tr> <tr style="line-height:25px"> <td style="line-height:25px"><span style="color:#003366; line-height:25px">jdk1.6.0_01</span></td> <td style="line-height:25px"><span style="color:#003366; line-height:25px">-target 1.4 -source 1.4</span></td> <td style="line-height:25px"><span style="color:#003366; line-height:25px">00 00 00 30</span></td> <td style="line-height:25px"><span style="color:#003366; line-height:25px">48.0</span></td> </tr> <tr style="line-height:25px"> <td style="line-height:25px"><span style="color:#003366; line-height:25px">jdk1.7.0</span></td> <td style="line-height:25px"><span style="color:#003366; line-height:25px">不带(默认为 -target 1.6)</span></td> <td style="line-height:25px"><span style="color:#003366; line-height:25px">00 00 00 32</span></td> <td style="line-height:25px"><span style="color:#003366; line-height:25px">50.0</span></td> </tr> <tr style="line-height:25px"> <td style="line-height:25px"><span style="color:#003366; line-height:25px">jdk1.7.0</span></td> <td style="line-height:25px"><span style="color:#003366; line-height:25px">-target 1.7</span></td> <td style="line-height:25px"><span style="color:#003366; line-height:25px">00 00 00 33</span></td> <td style="line-height:25px"><span style="color:#003366; line-height:25px">51.0</span></td> </tr> <tr style="line-height:25px"> <td style="line-height:25px"><span style="color:#003366; line-height:25px">jdk1.7.0</span></td> <td style="line-height:25px"><span style="color:#003366; line-height:25px">-target 1.4 -source 1.4</span></td> <td style="line-height:25px"><span style="color:#003366; line-height:25px">00 00 00 30</span></td> <td style="line-height:25px"><span style="color:#003366; line-height:25px">48.0</span></td> </tr> <tr style="line-height:25px"> <td style="line-height:25px"><span style="color:#003366; line-height:25px">Apache Harmony 5.0M3</span></td> <td style="line-height:25px"><span style="color:#003366; line-height:25px">不带(默认为 -target 1.2)</span></td> <td style="line-height:25px"><span style="color:#003366; line-height:25px">00 00 00 2E</span></td> <td style="line-height:25px"><span style="color:#003366; line-height:25px">46.0</span></td> </tr> <tr style="line-height:25px"> <td style="line-height:25px"><span style="color:#003366; line-height:25px">Apache Harmony 5.0M3</span></td> <td style="line-height:25px"><span style="color:#003366; line-height:25px">-target 1.4</span></td> <td style="line-height:25px"><span style="color:#003366; line-height:25px">00 00 00 30</span></td> <td style="line-height:25px"><span style="color:#003366; line-height:25px">48.0<br style="line-height:25px"></span></td> </tr> </tbody></table> <span style="line-height:25px">注1：</span><span style="color:#003366; line-height:25px">javac 有个 -target 参数，编译时可以通过</span><span style="color:#003366; line-height:25px"><span style="line-height:21px; font-family:verdana,sans-serif"><span style="line-height:22px">target</span></span><span style="line-height:21px; font-family:verdana,sans-serif">参数来设置编译时所使用的jdk版本。比如如果目标 JVM 是 1.3 的话，编译选项就可以用 -target 1.3 -source 1.3 了。</span></span> </div> <div style="line-height:25px"><span style="line-height:21px; font-family:verdana,sans-serif"><span style="line-height:21px"><span style="color:#003366; line-height:25px">相应的如果使用 ant ，<span style="line-height:25px; font-family:Arial,Helvetica,sans-serif; color:rgb(0,0,0)"><span style="line-height:21px; font-family:verdana,sans-serif"><span style="color:#003366; line-height:22px">编译时可以通过</span></span><span style="color:#003366; line-height:22px"><span style="line-height:21px; font-family:verdana,sans-serif"><span style="line-height:22px">target</span></span><span style="line-height:21px; font-family:verdana,sans-serif">参数来设置编译时所使用的jdk版本。比如：</span></span></span><br style="line-height:25px"> &lt;javac target="1.4" source="1.4" ............................/&gt;</span></span></span></div> <div style="line-height:25px"> <span style="line-height:21px; font-family:verdana,sans-serif"><span style="line-height:21px"><span style="line-height:25px">注2</span><span style="color:#003366; line-height:25px">：javac中</span></span></span><span style="color:#003366; line-height:25px"><span style="line-height:21px; font-family:verdana,sans-serif">source和</span><span style="line-height:21px; font-family:verdana,sans-serif">target 的意义</span></span> </div> <div style="line-height:25px"><span style="color:#FF6600; line-height:25px"><span style="line-height:21px; font-family:verdana,sans-serif"><span style="line-height:21px"></span></span><span style="line-height:21px; font-family:verdana,sans-serif">-source &lt;版本&gt; 提供与指定版本的源兼容性</span></span></div> <span style="line-height:21px; font-family:verdana,sans-serif"><span style="color:#FF6600; line-height:25px">-target &lt;版本&gt; 生成特定 VM 版本的类文件</span></span> <div style="line-height:25px"><span style="color:#993300; line-height:25px"><span style="line-height:21px; font-family:verdana,sans-serif">source才是真正的指明代码的兼容性，</span><span style="line-height:21px; font-family:verdana,sans-serif">target则是指定了生成class的格式的版本号，即</span><span style="line-height:21px; font-family:verdana,sans-serif">生成特定 VM 版本的类文件。</span></span></div> </wbr>