概述

.java 文件被编译器编译为 .class 文件，.class 文件具有特定的数据结构，如下表所示：ClassFile文件结构.png
每个 .class 文件都是以上表进行排序。

解析一个 .class 文件

使用 javap -verbose 命令可以查看 .class 文件的字节码：

  1. Classfile /E:/01_Code/Clarence_Code/Algorithm/output/zuo/Jvm.class
  2.   Last modified 2021-7-12; size 587 bytes
  3.   MD5 checksum 23bdf14592c29c18f8829d63ea6a70fb
  4.   Compiled from "Jvm.java"
  5. public class zuo.Jvm
  6.   minor version: 0
  7.   major version: 52
  8.   flags: ACC_PUBLIC, ACC_SUPER
  9. Constant pool:
  10.    #1 = Methodref          #6.#23         // java/lang/Object."<init>":()V
  11.    #2 = Fieldref           #24.#25        // java/lang/System.out:Ljava/io/PrintStream;
  12.    #3 = Class              #26            // zuo/Jvm
  13.    #4 = String             #27            // Hello World
  14.    #5 = Methodref          #28.#29        // java/io/PrintStream.println:(Ljava/lang/String;)V
  15.    #6 = Class              #30            // java/lang/Object
  16.    #7 = Utf8               HELLO_WORLD
  17.    #8 = Utf8               Ljava/lang/String;
  18.    #9 = Utf8               ConstantValue
  19.   #10 = Utf8               <init>
  20.   #11 = Utf8               ()V
  21.   #12 = Utf8               Code
  22.   #13 = Utf8               LineNumberTable
  23.   #14 = Utf8               LocalVariableTable
  24.   #15 = Utf8               this
  25.   #16 = Utf8               Lzuo/Jvm;
  26.   #17 = Utf8               main
  27.   #18 = Utf8               ([Ljava/lang/String;)V
  28.   #19 = Utf8               args
  29.   #20 = Utf8               [Ljava/lang/String;
  30.   #21 = Utf8               SourceFile
  31.   #22 = Utf8               Jvm.java
  32.   #23 = NameAndType        #10:#11        // "<init>":()V
  33.   #24 = Class              #31            // java/lang/System
  34.   #25 = NameAndType        #32:#33        // out:Ljava/io/PrintStream;
  35.   #26 = Utf8               zuo/Jvm
  36.   #27 = Utf8               Hello World
  37.   #28 = Class              #34            // java/io/PrintStream
  38.   #29 = NameAndType        #35:#36        // println:(Ljava/lang/String;)V
  39.   #30 = Utf8               java/lang/Object
  40.   #31 = Utf8               java/lang/System
  41.   #32 = Utf8               out
  42.   #33 = Utf8               Ljava/io/PrintStream;
  43.   #34 = Utf8               java/io/PrintStream
  44.   #35 = Utf8               println
  45.   #36 = Utf8               (Ljava/lang/String;)V
  46. {
  47.   public zuo.Jvm();
  48.     descriptor: ()V
  49.     flags: ACC_PUBLIC
  50.     Code:
  51.       stack=1, locals=1, args_size=1
  52.          0: aload_0
  53.          1: invokespecial #1                  // Method java/lang/Object."<init>":()V
  54.          4: return
  55.       LineNumberTable:
  56.         line 3: 0
  57.       LocalVariableTable:
  58.         Start  Length  Slot  Name   Signature
  59.             0       5     0  this   Lzuo/Jvm;
  61.   public static void main(java.lang.String[]);
  62.     descriptor: ([Ljava/lang/String;)V
  63.     flags: ACC_PUBLIC, ACC_STATIC
  64.     Code:
  65.       stack=2, locals=1, args_size=1
  66.          0: getstatic     #2                  // Field java/lang/System.out:Ljava/io/PrintStream;
  67.          3: ldc           #4                  // String Hello World
  68.          5: invokevirtual #5                  // Method java/io/PrintStream.println:(Ljava/lang/String;)V
  69.          8: return
  70.       LineNumberTable:
  71.         line 7: 0
  72.         line 8: 8
  73.       LocalVariableTable:
  74.         Start  Length  Slot  Name   Signature
  75.             0       9     0  args   [Ljava/lang/String;
  76. }
  77. SourceFile: "Jvm.java"