JVM字节码

public class Test1 {
public static void main(String[] args) {
int a = 2;
int b = 5;
int c = b - a;
System.out.println(c);
}
}

javap -v Test1.class > Test1.txt 
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　　

Classfile /root/study/workspace/Test1.class
Last modified Aug 6, 2019; size 579 bytes
MD5 checksum a96ef22100a65dc41cf1fda3e995d015
Compiled from "Test1.java"
public class com.lailai.jvm.Test1
minor version: 0
major version: 52
flags: ACC_PUBLIC, ACC_SUPER
Constant pool:
#1 = Methodref #5.#23 // java/lang/Object."<init>":()V
#2 = Fieldref #24.#25 // java/lang/System.out:Ljava/io/PrintStream;
#3 = Methodref #26.#27 // java/io/PrintStream.println:(I)V
#4 = Class #28 // com/lailai/jvm/Test1
#5 = Class #29 // java/lang/Object
#6 = Utf8 <init>
#7 = Utf8 ()V
#8 = Utf8 Code
#9 = Utf8 LineNumberTable
#10 = Utf8 LocalVariableTable
#11 = Utf8 this
#12 = Utf8 Lcom/lailai/jvm/Test1;
#13 = Utf8 main
#14 = Utf8 ([Ljava/lang/String;)V
#15 = Utf8 args
#16 = Utf8 [Ljava/lang/String;
#17 = Utf8 a
#18 = Utf8 I
#19 = Utf8 b
#20 = Utf8 c
#21 = Utf8 SourceFile
#22 = Utf8 Test1.java
#23 = NameAndType #6:#7 // "<init>":()V
#24 = Class #30 // java/lang/System
#25 = NameAndType #31:#32 // out:Ljava/io/PrintStream;
#26 = Class #33 // java/io/PrintStream
#27 = NameAndType #34:#35 // println:(I)V
#28 = Utf8 com/lailai/jvm/Test1
#29 = Utf8 java/lang/Object
#30 = Utf8 java/lang/System
#31 = Utf8 out
#32 = Utf8 Ljava/io/PrintStream;
#33 = Utf8 java/io/PrintStream
#34 = Utf8 println
#35 = Utf8 (I)V
{
public com.lailai.jvm.Test1();
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/lailai/jvm/Test1;

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: iconst_2
1: istore_1
2: iconst_5
3: istore_2
4: iload_2
5: iload_1
6: isub
7: istore_3
8: getstatic #2 // Field java/lang/System.out:Ljava/io/PrintStream;
11: iload_3
12: invokevirtual #3 // Method java/io/PrintStream.println:(I)V
15: return
LineNumberTable:
line 6: 0
line 7: 2
line 8: 4
line 9: 8
line 10: 15
LocalVariableTable:
Start Length Slot Name Signature
0 16 0 args [Ljava/lang/String;
2 14 1 a I
4 12 2 b I
8 8 3 c I
}
SourceFile: "Test1.java"

Object m(int i, double d, Thread t) {...}

(IDLjava/lang/Thread;)Ljava/lang/Object

public static void main(java.lang.String[]);
descriptor: ([Ljava/lang/String;)V    //方法描述，V表示该方法的返回值为void
flags: ACC_PUBLIC, ACC_STATIC    //方法修饰符，public、static的
Code:
stack=2, locals=4, args_size=1    //stack=2，操作栈大小为2、locals=4，本地变量大小，args_size=1，参数的个数
0: iconst_2    //将数字2压入操作栈，位于栈的最上面
1: istore_1    //从操作栈中弹出一个元素（数字2），放入本地变量表中，位于下标为1的位置（下标为0的是this）
2: iconst_5    //将数字5压入操作栈，位于栈的最上面
3: istore_2    //从操作栈中弹出一个元素（数字5），放入本地变量表中，位于下标为2的位置
4: iload_2    //将本地变量表中下标为2的位置的元素压入操作栈（5）
5: iload_1    //将本地变量表中下标为1的位置的元素压入操作栈（2）
6: isub    //操作栈中的2歌数字相减
7: istore_3    //将相减的结果压入到本地变量表中，位于下标为3的位置
//通过#2号在Constant pool中找到对应的常量，即可找到对应的引用
8: getstatic #2 // Field java/lang/System.out:Ljava/io/PrintStream;
11: iload_3    //将本地变量表中下标为3的位置的元素压入操作栈（3）
//通过#3号在Constant pool中找到对应的常量，即可找到对应的引用，进行方法调用
12: invokevirtual #3 // Method java/io/PrintStream.println:(I)V
15: return    //返回
LineNumberTable:    //行号的列表
line 6: 0
line 7: 2
line 8: 4
line 9: 8
line 10: 15
LocalVariableTable:    //本地变量表
Start Length Slot Name Signature
0 16 0 args [Ljava/lang/String;
2 14 1 a I
4 12 2 b I
8 8 3 c I
}
SourceFile: "Test1.java"