第六章+类文件结构+javap

使用javap打印常量表和计算字节码指令

javap 介绍

javap是 JDK自带的一个工具，可以将 class文件反编译成字节码，它并没有将class文件反编译成 java文件，但是依然反编译成程序员能读的格式。

1，编译源程序

源程序（我使用的是myeclipse）：

package t;

public class TestClass{
	private int m;
	
	public int inc(){
		return m+1;
	}
}

在myeclipse中，编译源程序：

必须确保你的myeclipse中菜单-->project(项目)--> build automatically (自动构建)这一项被选中打勾这样你写代码的时候,按下ctrl+S(保存) ,系统就会自动帮你编译,就是生成了TestClass.class字节码文件，才能使用javap

查看TestClass.class的文件位置

2，cmd 进入class目录， javap -verbose classname

书中代码清单6-2和6-4

Microsoft Windows [版本 10.0.17763.316]
(c) 2018 Microsoft Corporation。保留所有权利。

C:\Users\ee>
C:\Users\ee>cd Workspaces/MyEclipse 10/TEST/bin/t/

C:\Users\ee\Workspaces\MyEclipse 10\TEST\bin\t>javap -verbose TestClass
警告: 二进制文件TestClass包含t.TestClass
Classfile /C:/Users/ee/Workspaces/MyEclipse 10/TEST/bin/t/TestClass.class
  Last modified 2019-3-7; size 357 bytes
  MD5 checksum 63be3f690d4eb235eaf51ab7529a6462
  Compiled from "TestClass.java"
public class t.TestClass
  SourceFile: "TestClass.java"
  minor version: 0
  major version: 51
  flags: ACC_PUBLIC, ACC_SUPER
Constant pool:
   #1 = Class              #2             //  t/TestClass
   #2 = Utf8               t/TestClass
   #3 = Class              #4             //  java/lang/Object
   #4 = Utf8               java/lang/Object
   #5 = Utf8               m
   #6 = Utf8               I
   #7 = Utf8               <init>
   #8 = Utf8               ()V
   #9 = Utf8               Code
  #10 = Methodref          #3.#11         //  java/lang/Object."<init>":()V
  #11 = NameAndType        #7:#8          //  "<init>":()V
  #12 = Utf8               LineNumberTable
  #13 = Utf8               LocalVariableTable
  #14 = Utf8               this
  #15 = Utf8               Lt/TestClass;
  #16 = Utf8               inc
  #17 = Utf8               ()I
  #18 = Fieldref           #1.#19         //  t/TestClass.m:I
  #19 = NameAndType        #5:#6          //  m:I
  #20 = Utf8               SourceFile
  #21 = Utf8               TestClass.java
{
  public t.TestClass();
    flags: ACC_PUBLIC
    Code:
      stack=1, locals=1, args_size=1
         0: aload_0
         1: invokespecial #10                 // Method java/lang/Object."<init>":()V
         4: return
      LineNumberTable:
        line 3: 0
      LocalVariableTable:
        Start  Length  Slot  Name   Signature
               0       5     0  this   Lt/TestClass;

  public int inc();
    flags: ACC_PUBLIC
    Code:
      stack=2, locals=1, args_size=1
         0: aload_0
         1: getfield      #18                 // Field m:I
         4: iconst_1
         5: iadd
         6: ireturn
      LineNumberTable:
        line 7: 0
      LocalVariableTable:
        Start  Length  Slot  Name   Signature
               0       7     0  this   Lt/TestClass;
}

C:\Users\ee\Workspaces\MyEclipse 10\TEST\bin\t>

还有一些javac的东西，没遇到，懒得写，附上别人博客