Class类文件结构解读——常量池

首先写一个Java文件

public class HelloWorld{
    private int m;
    public int intc(){
        return m + 1;
    }
}

使用javac编译为class文件

C:\Users\xiaoqiu\Desktop>javac HelloWorld.java

使用十六进制编辑器winHex打开class文件

 

上面我们人工读class文件实在是一个比较繁琐并且吃力的活，下面我们采用javap -verbose 来读取

C:\Users\xiaoqiu\Desktop>javap -verbose HelloWorld.class
Classfile /C:/Users/xiaoqiu/Desktop/HelloWorld.class
  Last modified 2019-1-26; size 278 bytes
  MD5 checksum 0a90643d0d7ef2078965014eca999f28
  Compiled from "HelloWorld.java"
public class HelloWorld
  minor version: 0
  major version: 52#主版本号
  flags: ACC_PUBLIC, ACC_SUPER
Constant pool:#常量池 可以看出和我们读的结果是一样的
   #1 = Methodref          #4.#15         // java/lang/Object."<init>":()V
   #2 = Fieldref           #3.#16         // HelloWorld.m:I
   #3 = Class              #17            // HelloWorld
   #4 = Class              #18            // java/lang/Object
   #5 = Utf8               m
   #6 = Utf8               I
   #7 = Utf8               <init>
   #8 = Utf8               ()V
   #9 = Utf8               Code
  #10 = Utf8               LineNumberTable
  #11 = Utf8               intc
  #12 = Utf8               ()I
  #13 = Utf8               SourceFile
  #14 = Utf8               HelloWorld.java
  #15 = NameAndType        #7:#8          // "<init>":()V
  #16 = NameAndType        #5:#6          // m:I
  #17 = Utf8               HelloWorld
  #18 = Utf8               java/lang/Object
{
  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 int intc();
    descriptor: ()I
    flags: ACC_PUBLIC
    Code:
      stack=2, locals=1, args_size=1
         0: aload_0
         1: getfield      #2                  // Field m:I
         4: iconst_1
         5: iadd
         6: ireturn
      LineNumberTable:
        line 4: 0
}
SourceFile: "HelloWorld.java"

下面附上常量池的项目类型

 以及每种常量类型的结构