JVM 字节码的结构

Posted 2022-02-05 linlf03

编译的.class文件，可以用javap进行反编译

javap Test.class

javap -c Test.class

javap -verbose Test.class

 

1、创建MyTest1.java

public class MyTest1 
    private int a = 1;

    public MyTest1() 
    

    public int getA() 
        return this.a;
    

    public void setA(int a) 
        this.a = a;
    

使用D:\\workspace\\study\\ jvm_demo\\build\\classes\\java\\main\\com\\example\\jvm\\bytecode>javap -verbose  MyTest1.class

Classfile /D:/workspace/study/ jvm_demo/build/classes/java/main/com/example/jvm/bytecode/MyTest1.class
  Last modified 2019-6-23; size 495 bytes
  MD5 checksum 54c0850cfabb7f115919c93e556e3630
  Compiled from "MyTest1.java"
public class com.example.jvm.bytecode.MyTest1
  SourceFile: "MyTest1.java"
  minor version: 0
  major version: 51
  flags: ACC_PUBLIC, ACC_SUPER
Constant pool:
   #1 = Methodref          #4.#20         //  java/lang/Object."<init>":()V
   #2 = Fieldref           #3.#21         //  com/example/jvm/bytecode/MyTest1.a:I
   #3 = Class              #22            //  com/example/jvm/bytecode/MyTest1
   #4 = Class              #23            //  java/lang/Object
   #5 = Utf8               a
   #6 = Utf8               I
   #7 = Utf8               <init>
   #8 = Utf8               ()V
   #9 = Utf8               Code
  #10 = Utf8               LineNumberTable
  #11 = Utf8               LocalVariableTable
  #12 = Utf8               this
  #13 = Utf8               Lcom/example/jvm/bytecode/MyTest1;
  #14 = Utf8               getA
  #15 = Utf8               ()I
  #16 = Utf8               setA
  #17 = Utf8               (I)V
  #18 = Utf8               SourceFile
  #19 = Utf8               MyTest1.java
  #20 = NameAndType        #7:#8          //  "<init>":()V
  #21 = NameAndType        #5:#6          //  a:I
  #22 = Utf8               com/example/jvm/bytecode/MyTest1
  #23 = Utf8               java/lang/Object

  public com.example.jvm.bytecode.MyTest1();
    flags: ACC_PUBLIC
    Code:
      stack=2, locals=1, args_size=1
         0: aload_0
         1: invokespecial #1                  // Method java/lang/Object."<init>":()V
         4: aload_0
         5: iconst_1
         6: putfield      #2                  // Field a:I
         9: return
      LineNumberTable:
        line 6: 0
        line 8: 4
      LocalVariableTable:
        Start  Length  Slot  Name   Signature
               0      10     0  this   Lcom/example/jvm/bytecode/MyTest1;

  public int getA();
    flags: ACC_PUBLIC
    Code:
      stack=1, locals=1, args_size=1
         0: aload_0
         1: getfield      #2                  // Field a:I
         4: ireturn
      LineNumberTable:
        line 12: 0
      LocalVariableTable:
        Start  Length  Slot  Name   Signature
               0       5     0  this   Lcom/example/jvm/bytecode/MyTest1;

  public void setA(int);
    flags: ACC_PUBLIC
    Code:
      stack=2, locals=2, args_size=2
         0: aload_0
         1: iload_1
         2: putfield      #2                  // Field a:I
         5: return
      LineNumberTable:
        line 16: 0
        line 17: 5
      LocalVariableTable:
        Start  Length  Slot  Name   Signature
               0       6     0  this   Lcom/example/jvm/bytecode/MyTest1;
               0       6     1     a   I

　　

2、使用WinHex打开MyTest1.class文件

 

1、使用javap -verbose命令分析一个字节码文件时，将会分析该字节码文件的魔数、版本号、常量池、类的构造方法、类中的方法信息、类变量与成员变量等信息。
2、魔数： 所有的.class字节码文件的前4个字节都是魔数，魔数值为固定值： 0xCAFEBABE.
3、

 

 

 

3、Class文件结构中常量池中11种数据类型的结构总表