javap 反编译工具-查看java编译器生成的字节码

用法: javap <options> <classes>
其中, 可能的选项包括:
  -help  --help  -?        输出此用法消息
  -version                 版本信息
  -v  -verbose             输出附加信息
  -l                       输出行号和本地变量表
  -public                  仅显示公共类和成员
  -protected               显示受保护的/公共类和成员
  -package                 显示程序包/受保护的/公共类
                           和成员 (默认)
  -p  -private             显示所有类和成员
  -c                       对代码进行反汇编
  -s                       输出内部类型签名
  -sysinfo                 显示正在处理的类的
                           系统信息 (路径, 大小, 日期, MD5 散列)
  -constants               显示最终常量
  -classpath <path>        指定查找用户类文件的位置
  -cp <path>               指定查找用户类文件的位置
  -bootclasspath <path>    覆盖引导类文件的位置

 有如下类：

public class Test2 {
    public static void main(String[] args) {
        int i = 10;
        int j = 20;
        int k = i + j;
    }
}

执行javap -v Test2.class

PS D:\04_web_dev2\tt\server\target\classes\com\tso> javap -v .\Test2.class
Classfile /D:/04_web_dev2/tt/server/target/classes/com/tso/Test2.class
  Last modified 2022-10-8; size 472 bytes
  MD5 checksum d1352a4eebc98ac8507a1e7ee3ecb5d7
  Compiled from "Test2.java"
public class com.tso.Test2
  minor version: 0
  major version: 52
  flags: ACC_PUBLIC, ACC_SUPER
Constant pool:
   #1 = Methodref          #3.#22         // java/lang/Object."<init>":()V
   #2 = Class              #23            // com/tso/Test2
   #3 = Class              #24            // java/lang/Object
   #4 = Utf8               <init>
   #5 = Utf8               ()V
   #6 = Utf8               Code
   #7 = Utf8               LineNumberTable
   #8 = Utf8               LocalVariableTable
   #9 = Utf8               this
  #10 = Utf8               Lcom/tso/Test2;
  #11 = Utf8               main
  #12 = Utf8               ([Ljava/lang/String;)V
  #13 = Utf8               args
  #14 = Utf8               [Ljava/lang/String;
  #15 = Utf8               i
  #16 = Utf8               I
  #17 = Utf8               j
  #18 = Utf8               k
  #19 = Utf8               MethodParameters
  #20 = Utf8               SourceFile
  #21 = Utf8               Test2.java
  #22 = NameAndType        #4:#5          // "<init>":()V
  #23 = Utf8               com/tso/Test2
  #24 = Utf8               java/lang/Object
{
  public com.tso.Test2();
    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 3: 0
      LocalVariableTable:
        Start  Length  Slot  Name   Signature
            0       5     0  this   Lcom/tso/Test2;

  public static void main(java.lang.String[]);
    descriptor: ([Ljava/lang/String;)V
    flags: ACC_PUBLIC, ACC_STATIC
    Code:
      stack=2, locals=4, 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_3
        10: return
      LineNumberTable:
        line 5: 0
        line 6: 3
        line 7: 6
        line 8: 10
      LocalVariableTable:
        Start  Length  Slot  Name   Signature
            0      11     0  args   [Ljava/lang/String;
            3       8     1     i   I
            6       5     2     j   I
           10       1     3     k   I
    MethodParameters:
      Name                           Flags
      args
}
SourceFile: "Test2.java"

重点查看main方法的字节码：

 public static void main(java.lang.String[]);
    descriptor: ([Ljava/lang/String;)V
    flags: ACC_PUBLIC, ACC_STATIC
    Code:
      stack=2, locals=4, 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_3
        10: return