生成字节码文件并查看

查看字节码文件的方式：javac 文件名.java 即可生成.class文件,但是这种方式不方便

java：是运行字节码文件；由java虚拟机对字节码进行解释和运行。
javac：是编译命令，将java源文件编译成.class字节码文件。
javap是 Java class文件分解器，可以反编译，也可以查看java编译器生成的字节码。

package demo;

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

生成字节码文件：javap -v -l -c HelloWorld.class

D:\Java\WorkSpace\Idea\s01\src\demo>javap-v-l-c HelloWorld.

class
Classfile /D:/Java/WorkSpace/Idea/s01/src/demo/HelloWorld.

class
Last modified 2021-7-23;size 413bytes
        MD5 checksum b247ab468b1e57da5311382960716000
        Compiled from"HelloWorld.java"

public class demo.HelloWorld
        minor version:0
        major version:52
        flags:ACC_PUBLIC,ACC_SUPER
        Constant pool:
        #1=Methodref          #5.#14         // java/lang/Object."<init>":()V
        #2=Fieldref           #15.#16        // java/lang/System.out:Ljava/io/PrintStream;
        #3=Class              #17            // demo/HelloWorld
        #4=Methodref          #18.#19        // java/io/PrintStream.println:(Ljava/lang/Object;)V
        #5=Class              #20            // java/lang/Object
        #6=Utf8<init>
   #7=Utf8()V
           #8=Utf8 Code
           #9=Utf8 LineNumberTable
           #10=Utf8 main
           #11=Utf8([Ljava/lang/String;)V
           #12=Utf8 SourceFile
           #13=Utf8 HelloWorld.java
           #14=NameAndType        #6:#7          // "<init>":()V
           #15=Class              #21            // java/lang/System
           #16=NameAndType        #22:#23        // out:Ljava/io/PrintStream;
           #17=Utf8 demo/HelloWorld
           #18=Class              #24            // java/io/PrintStream
           #19=NameAndType        #25:#26        // println:(Ljava/lang/Object;)V
           #20=Utf8 java/lang/Object
           #21=Utf8 java/lang/System
           #22=Utf8 out
           #23=Utf8 Ljava/io/PrintStream;
           #24=Utf8 java/io/PrintStream
           #25=Utf8 println
           #26=Utf8(Ljava/lang/Object;)V
           {
public demo.HelloWorld();
        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

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                  // class demo/HelloWorld
        5:invokevirtual #4                  // Method java/io/PrintStream.println:(Ljava/lang/Object;)V
        8:return
        LineNumberTable:
        line 5:0
        line 6:8
        }
        SourceFile:"HelloWorld.java"

idea字节码插件JClassLibJ——阅读JVM字节码

在idea中可以安装JClassLib插件，使字节码文件更具有可读性

view-> showByteCodewith JClassLib

public class Sample {
    private final String name;
    private final int age;
    private final double number = 0.0;
    public Sample(String name , int age){
        this.name = name;
        this.age = age;
    }

    public void output(String call){
        System.out.println(call + "姓名:" + name);
        System.out.println(call + "年龄:" + age);
    }

    public String output1(String call){
        System.out.println(call + "姓名:" + name);
        System.out.println(call + "年龄:" + age);
        return "SUCCESS";
    }

    public static void main(String[] args) {
        new Sample("小明" , 36).output("你好");
        new Sample("小红" , 36).output1("Hello");
    }
}