015-JVM-使用javap查看class文件内容

处理使用上面的工具还可以使用 javap 查看 class 文件的格式

Microsoft Windows [版本 10.0.19041.685]
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D:\MCA\JVM\out\production\JVM\com\yuhl>javap -v Helloword.class
Classfile /D:/MCA/JVM/out/production/JVM/com/yuhl/Helloword.class
  Last modified 2020-12-19; size 547 bytes
  MD5 checksum 0d5b91ddd1f20c608a7cabc0eb01efec
  Compiled from "Helloword.java"
public class com.yuhl.Helloword
  minor version: 0
  major version: 52
  flags: ACC_PUBLIC, ACC_SUPER
Constant pool:
   #1 = Methodref          #6.#20         // java/lang/Object."<init>":()V
   #2 = Fieldref           #21.#22        // java/lang/System.out:Ljava/io/PrintStream;
   #3 = String             #23            // Helloword!
   #4 = Methodref          #24.#25        // java/io/PrintStream.println:(Ljava/lang/String;)V
   #5 = Class              #26            // com/yuhl/Helloword
   #6 = Class              #27            // java/lang/Object
   #7 = Utf8               <init>
   #8 = Utf8               ()V
   #9 = Utf8               Code
  #10 = Utf8               LineNumberTable
  #11 = Utf8               LocalVariableTable
  #12 = Utf8               this
  #13 = Utf8               Lcom/yuhl/Helloword;
  #14 = Utf8               main
  #15 = Utf8               ([Ljava/lang/String;)V
  #16 = Utf8               args
  #17 = Utf8               [Ljava/lang/String;
  #18 = Utf8               SourceFile
  #19 = Utf8               Helloword.java
  #20 = NameAndType        #7:#8          // "<init>":()V
  #21 = Class              #28            // java/lang/System
  #22 = NameAndType        #29:#30        // out:Ljava/io/PrintStream;
  #23 = Utf8               Helloword!
  #24 = Class              #31            // java/io/PrintStream
  #25 = NameAndType        #32:#33        // println:(Ljava/lang/String;)V
  #26 = Utf8               com/yuhl/Helloword
  #27 = Utf8               java/lang/Object
  #28 = Utf8               java/lang/System
  #29 = Utf8               out
  #30 = Utf8               Ljava/io/PrintStream;
  #31 = Utf8               java/io/PrintStream
  #32 = Utf8               println
  #33 = Utf8               (Ljava/lang/String;)V
{
  public com.yuhl.Helloword();
    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 9: 0
      LocalVariableTable:
        Start  Length  Slot  Name   Signature
            0       5     0  this   Lcom/yuhl/Helloword;

  public static void main(java.lang.String[]);
    descriptor: ([Ljava/lang/String;)V
    flags: ACC_PUBLIC, ACC_STATIC
    Code:
      stack=2, locals=1, args_size=1
         0: getstatic     #2                  // Field java/lang/System.out:Ljava/io/PrintStream;
         3: ldc           #3                  // String Helloword!
         5: invokevirtual #4                  // Method java/io/PrintStream.println:(Ljava/lang/String;)V
         8: return
      LineNumberTable:
        line 11: 0
        line 12: 8
      LocalVariableTable:
        Start  Length  Slot  Name   Signature
            0       9     0  args   [Ljava/lang/String;
}
SourceFile: "Helloword.java"

D:\MCA\JVM\out\production\JVM\com\yuhl>

简单说明：

1. Classfile：类文件
2. Constant pool: 常量池
3. SourceFile: 源文件

因为这 java 类写的比较简单，所以很多信息是没有的，但是遇到问题就参考前面的字典就可以解读了
014-JVM-Class 文件结构概况 https://blog.csdn.net/fsjwin/article/details/111422262

2.1 效果

external tools 添加很简单，自行解决之：

看到的效果和使用命令一样的

自律的艰辛总甜过懊悔的苦果！
专注于 java 后端技术及解决方案，善于总结，分享！
自律的艰辛总甜过懊悔的苦果！
专注于 java 后端技术及解决方案，善于总结，分享！
自律的艰辛总甜过懊悔的苦果！
专注于 java 后端技术及解决方案，善于总结，分享！