JVM 真香系列：轻松理解 class 文件到虚拟机（上）

public class HelloWorld {    public static void main(String[] args) {        System.out.println("Hello world");    }}

javac HelloWorld.java

package com.tian.demo.test;public class User {    private int age = 22;    private String name = "tian";    public int addAge() {        return age = age + 1;    }    public static void main(String[] args) {    }}

javap -v User.class >log.txt

Classfile /D:/workspace/new/demo/src/main/java/com/tian/demo/test/User.class  Last modified 2020-11-5; size 441 bytes  MD5 checksum 2fa72d3f53bd9f138e0bfae82aba67e3  Compiled from "User.java"public class com.tian.demo.test.User  minor version: 0  major version: 52  flags: ACC_PUBLIC, ACC_SUPERConstant pool:   #1 = Methodref          #6.#21         // java/lang/Object."<init>":()V   #2 = Fieldref           #5.#22         // com/tian/demo/test/User.age:I   #3 = String             #23            // tian   #4 = Fieldref           #5.#24         // com/tian/demo/test/User.name:Ljava/lang/String;   #5 = Class              #25            // com/tian/demo/test/User   #6 = Class              #26            // java/lang/Object   #7 = Utf8               age   #8 = Utf8               I   #9 = Utf8               name  #10 = Utf8               Ljava/lang/String;  #11 = Utf8               <init>  #12 = Utf8               ()V  #13 = Utf8               Code  #14 = Utf8               LineNumberTable  #15 = Utf8               addAge  #16 = Utf8               ()I  #17 = Utf8               main  #18 = Utf8               ([Ljava/lang/String;)V  #19 = Utf8               SourceFile  #20 = Utf8               User.java  #21 = NameAndType        #11:#12        // "<init>":()V  #22 = NameAndType        #7:#8          // age:I  #23 = Utf8               tian  #24 = NameAndType        #9:#10         // name:Ljava/lang/String;  #25 = Utf8               com/tian/demo/test/User  #26 = Utf8               java/lang/Object{  public com.tian.demo.test.User();    descriptor: ()V    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: bipush        22         7: putfield      #2                  // Field age:I        10: aload_0        11: ldc           #3                  // String tian        13: putfield      #4                  // Field name:Ljava/lang/String;        16: return      LineNumberTable:        line 3: 0        line 4: 4        line 5: 10  public int addAge();    descriptor: ()I    flags: ACC_PUBLIC    Code:      stack=3, locals=1, args_size=1         0: aload_0         1: aload_0         2: getfield      #2                  // Field age:I         5: iconst_1         6: iadd         7: dup_x1         8: putfield      #2                  // Field age:I        11: ireturn      LineNumberTable:        line 8: 0  public static void main(java.lang.String[]);    descriptor: ([Ljava/lang/String;)V    flags: ACC_PUBLIC, ACC_STATIC    Code:      stack=0, locals=1, args_size=1         0: return      LineNumberTable:        line 13: 0}SourceFile: "User.java"