javap——查看class文件的方法

有时候为了研究Javac的原理，要去看看class文件的内容是如何组织的，这时候很有必要查看class文件。方法有很多种，这里推荐使用JDK自带的javap工具。 首先建立如下源码：

public class HelloWorld{     public static void main(String[] args){         System.out.println("hello world!");     } }

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使用javac编译器把源文件编译好，再接着使用javap工具查看class文件，命令如下 javap -verbose HelloWorld

这是DOS窗口的运行结果复制出来如下图：

F:\>javac HelloWorld.java

F:\>javap -verbose HelloWorld Classfile /F:/HelloWorld.class   Last modified 2017-12-24; size 426 bytes   MD5 checksum 4efac412ef483c8a3fe7489c87d15c8c   Compiled from "HelloWorld.java" public class HelloWorld   minor version: 0   major version: 52   flags: ACC_PUBLIC, ACC_SUPER Constant pool:    #1 = Methodref          #6.#15         // java/lang/Object."<init>":()V    #2 = Fieldref           #16.#17        // java/lang/System.out:Ljava/io/Print Stream;    #3 = String             #18            // hello world!    #4 = Methodref          #19.#20        // java/io/PrintStream.println:(Ljava/ lang/String;)V    #5 = Class              #21            // HelloWorld    #6 = Class              #22            // java/lang/Object    #7 = Utf8               <init>    #8 = Utf8               ()V    #9 = Utf8               Code   #10 = Utf8               LineNumberTable   #11 = Utf8               main   #12 = Utf8               ([Ljava/lang/String;)V   #13 = Utf8               SourceFile   #14 = Utf8               HelloWorld.java   #15 = NameAndType        #7:#8          // "<init>":()V   #16 = Class              #23            // java/lang/System   #17 = NameAndType        #24:#25        // out:Ljava/io/PrintStream;   #18 = Utf8               hello world!   #19 = Class              #26            // java/io/PrintStream   #20 = NameAndType        #27:#28        // println:(Ljava/lang/String;)V   #21 = Utf8               HelloWorld   #22 = Utf8               java/lang/Object   #23 = Utf8               java/lang/System   #24 = Utf8               out   #25 = Utf8               Ljava/io/PrintStream;   #26 = Utf8               java/io/PrintStream   #27 = Utf8               println   #28 = Utf8               (Ljava/lang/String;)V {   public HelloWorld();     descriptor: ()V     flags: ACC_PUBLIC     Code:       stack=1, locals=1, args_size=1          0: aload_0          1: invokespecial #1                  // Method java/lang/Object."<init> ":()V          4: return       LineNumberTable:         line 1: 0

  public static void main(java.lang.String[]);     descriptor: ([Ljava/lang/String;)V     flags: ACC_PUBLIC, ACC_STATIC     Code:       stack=2, locals=1, args_size=1          0: getstatic     #2                  // Field java/lang/System.out:Ljav a/io/PrintStream;          3: ldc           #3                  // String hello world!          5: invokevirtual #4                  // Method java/io/PrintStream.prin tln:(Ljava/lang/String;)V          8: return       LineNumberTable:         line 3: 0         line 4: 8 } SourceFile: "HelloWorld.java"

这样就是JVM规范的class文件了。结合这个对比源码可以深刻的认识到Javac的作用所在。 --------------------- 作者：tbc123tbc 来源： 原文：https://blog.csdn.net/tbc123tbc/article/details/78883213 版权声明：本文为博主原创文章，转载请附上博文链接！