生成一个class文件

出处：从一个class文件深入理解Java字节码结构
通过文章自己实践的
java源代码：

package hello;

public class Demo {
	private int num=1;
	
	public int add() {
		num=num+2;
		return num;
	}
	
}

class文件存在了：F:\java\workspace\hello\src\hello
之所以要进到src进行编译，是考虑到后面反编译时生成class类型对象方便

F:\>cd java

F:\java>cd workspace

F:\java\workspace>cd hello

F:\java\workspace\hello>cd src

F:\java\workspace\hello\src>javac hello/Demo.java

F:\java\workspace\hello\src>javap -verbose Demo.class
错误: 找不到类: Demo.class

F:\java\workspace\hello\src>cd hello

F:\java\workspace\hello\src\hello>javap -verbose Demo.class
Classfile /F:/java/workspace/hello/src/hello/Demo.class
  Last modified 2020-3-9; size 294 bytes
  MD5 checksum fde1585395e8356cc4fa817516b91ec8
  Compiled from "Demo.java"
public class hello.Demo
  minor version: 0
  major version: 52
  flags: ACC_PUBLIC, ACC_SUPER
Constant pool:
   #1 = Methodref          #4.#15         // java/lang/Object."<init>":()V
   #2 = Fieldref           #3.#16         // hello/Demo.num:I
   #3 = Class              #17            // hello/Demo
   #4 = Class              #18            // java/lang/Object
   #5 = Utf8               num
   #6 = Utf8               I
   #7 = Utf8               <init>
   #8 = Utf8               ()V
   #9 = Utf8               Code
  #10 = Utf8               LineNumberTable
  #11 = Utf8               add
  #12 = Utf8               ()I
  #13 = Utf8               SourceFile
  #14 = Utf8               Demo.java
  #15 = NameAndType        #7:#8          // "<init>":()V
  #16 = NameAndType        #5:#6          // num:I
  #17 = Utf8               hello/Demo
  #18 = Utf8               java/lang/Object
{
  public hello.Demo();
    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: iconst_1
         6: putfield      #2                  // Field num:I
         9: return
      LineNumberTable:
        line 3: 0
        line 4: 4

  public int add();
    descriptor: ()I
    flags: ACC_PUBLIC
    Code:
      stack=3, locals=1, args_size=1
         0: aload_0
         1: aload_0
         2: getfield      #2                  // Field num:I
         5: iconst_2
         6: iadd
         7: putfield      #2                  // Field num:I
        10: aload_0
        11: getfield      #2                  // Field num:I
        14: ireturn
      LineNumberTable:
        line 7: 0
        line 8: 10
}
SourceFile: "Demo.java"

F:\java\workspace\hello\src\hello>