C:\w>javap -verbose test
Compiled from "test.java"
public class test extends java.lang.Object
  SourceFile: "test.java"
  minor version: 0
  major version: 49
  Constant pool:        //常量池部分最看不懂,望详细些.
const #1 = Method       #5.#14; //  java/lang/Object."<init>":()V
const #2 = Field        #15.#16;        //  java/lang/System.out:Ljava/io/PrintS
tream;
const #3 = Method       #17.#18;        //  java/io/PrintStream.println:(I)V
const #4 = class        #19;    //  test
const #5 = class        #20;    //  java/lang/Object
const #6 = Asciz        <init>;
const #7 = Asciz        ()V;
const #8 = Asciz        Code;
const #9 = Asciz        LineNumberTable;
const #10 = Asciz       main;
const #11 = Asciz       ([Ljava/lang/String;)V;
const #12 = Asciz       SourceFile;
const #13 = Asciz       test.java;
const #14 = NameAndType #6:#7;//  "<init>":()V
const #15 = class       #21;    //  java/lang/System
const #16 = NameAndType #22:#23;//  out:Ljava/io/PrintStream;
const #17 = class       #24;    //  java/io/PrintStream
const #18 = NameAndType #25:#26;//  println:(I)V
const #19 = Asciz       test;
const #20 = Asciz       java/lang/Object;
const #21 = Asciz       java/lang/System;
const #22 = Asciz       out;
const #23 = Asciz       Ljava/io/PrintStream;;
const #24 = Asciz       java/io/PrintStream;
const #25 = Asciz       println;
const #26 = Asciz       (I)V;

{
public test();
  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 static void main(java.lang.String[]);
  Code:
   Stack=2, Locals=3, Args_size=1
   0:   bipush  10
   2:   istore_1
   3:   bipush  20
   5:   istore_2
   6:   iload_1
   7:   iload_2
   8:   iadd
   9:   istore_1
   10:  getstatic       #2; //Field java/lang/System.out:Ljava/io/PrintStream;
   13:  iload_1
   14:  invokevirtual   #3; //Method java/io/PrintStream.println:(I)V
   17:  return
  LineNumberTable:
   line 4: 0
   line 5: 3
   line 6: 6
   line 7: 10
   line 9: 17

}

public class test{
public static void main(String[] args){
int i,j;
i=10;
j=20;
i+=j;
System.out.println(i);

}

}