javap 反汇编

àì夳堔傛蜴生んèń 2023-10-08 13:02 34阅读 0赞

#### 文章目录 ####

*  1、把一个java类反汇编
 *   *  1.1、写一个类Hello.java
     *  1.2、javac 编译
     *  1.3、javap 反汇编
 *  2、分析汇编代码

## 1、把一个java类反汇编 ##

### 1.1、写一个类Hello.java ###

Hello.java

public class Hello {
        
        private Integer num1 = 0;
        private Integer num2;
    
        public Integer getNum(Integer num){
        
            this.num1 += num;
            this.num2 = num * 100;
            return num2 + num1;
        }
    
        public static void main(String[] args) {
        
            Hello h = new Hello();
            System.out.println(h.getNum(20));
        }
    }

### 1.2、javac 编译 ###

输入指令：javac Hello.java  
得到Hello.class

public class Hello {
        
        private Integer num1 = 0;
        private Integer num2;
    
        public Hello() {
        
        }
    
        public Integer getNum(Integer var1) {
        
            this.num1 = this.num1 + var1;
            this.num2 = var1 * 100;
            return this.num2 + this.num1;
        }
    
        public static void main(String[] var0) {
        
            Hello var1 = new Hello();
            System.out.println(var1.getNum(20));
        }
    }

### 1.3、javap 反汇编 ###

输入指令：javap -c Hello  
得到反汇编内容

警告: 二进制文件Hello包含Hello
    Compiled from "Hello.java"
    public class Hello {
        
      public Hello();
        Code:
           0: aload_0
           1: invokespecial #1                  // Method java/lang/Object."<init>":()V
           4: aload_0
           5: iconst_0
           6: invokestatic  #2                  // Method java/lang/Integer.valueOf:(I)Ljava/lang/Integer;
           9: putfield      #3                  // Field num1:Ljava/lang/Integer;
          12: return
    
      public java.lang.Integer getNum(java.lang.Integer);
        Code:
           0: aload_0
           1: astore_2
           2: aload_2
           3: aload_2
           4: getfield      #3                  // Field num1:Ljava/lang/Integer;
           7: invokevirtual #4                  // Method java/lang/Integer.intValue:()I
          10: aload_1
          11: invokevirtual #4                  // Method java/lang/Integer.intValue:()I
          14: iadd
          15: invokestatic  #2                  // Method java/lang/Integer.valueOf:(I)Ljava/lang/Integer;
          18: dup_x1
          19: putfield      #3                  // Field num1:Ljava/lang/Integer;
          22: pop
          23: aload_0
          24: aload_1
          25: invokevirtual #4                  // Method java/lang/Integer.intValue:()I
          28: bipush        100
          30: imul
          31: invokestatic  #2                  // Method java/lang/Integer.valueOf:(I)Ljava/lang/Integer;
          34: putfield      #5                  // Field num2:Ljava/lang/Integer;
          37: aload_0
          38: getfield      #5                  // Field num2:Ljava/lang/Integer;
          41: invokevirtual #4                  // Method java/lang/Integer.intValue:()I
          44: aload_0
          45: getfield      #3                  // Field num1:Ljava/lang/Integer;
          48: invokevirtual #4                  // Method java/lang/Integer.intValue:()I
          51: iadd
          52: invokestatic  #2                  // Method java/lang/Integer.valueOf:(I)Ljava/lang/Integer;
          55: areturn
    
      public static void main(java.lang.String[]);
        Code:
           0: new           #6                  // class Hello
           3: dup
           4: invokespecial #7                  // Method "<init>":()V
           7: astore_1
           8: getstatic     #8                  // Field java/lang/System.out:Ljava/io/PrintStream;
          11: aload_1
          12: bipush        20
          14: invokestatic  #2                  // Method java/lang/Integer.valueOf:(I)Ljava/lang/Integer;
          17: invokevirtual #9                  // Method getNum:(Ljava/lang/Integer;)Ljava/lang/Integer;
          20: invokevirtual #10                 // Method java/io/PrintStream.println:(Ljava/lang/Object;)V
          23: return
    }

## 2、分析汇编代码 ##

先看看里面方法大概有哪些

public class Hello {
        
      public Hello();                                           // 构造方法
        Code:
    ......
    
      public java.lang.Integer getNum(java.lang.Integer);
        Code:
    ......
    
      public static void main(java.lang.String[]);              // 主方法
        Code:
    ......
    }

看看构造方法的代码内容

public Hello();
        Code:
           0: aload_0                // 加载索引为0的变量的值
           1: invokespecial #1       
           4: aload_0
           5: iconst_0               //将常量0，压入到操作数栈
           6: invokestatic  #2      
           9: putfield      #3       
          12: return