http://blog.dengqinghua.net

-XX:+DisableExplicitGC
-XX:+PrintGCDetails
-XX:+PrintGCApplicationStoppedTime
-XX:+PrintGCApplicationConcurrentTime
-XX:+PrintGCDateStamps
-Xloggc:gclog.log
-XX:+UseGCLogFileRotation
-XX:NumberOfGCLogFiles=5
-XX:GCLogFileSize=2000k

git clone https://github.com/dengqinghua/my_examples.git
cd my_examples/java
mvn compile
javap -v target/classes/com/dengqinghua/calculate/Salary.class

package com.dengqinghua.calculate;

public class Salary {
    private int monthSalary;
    private int bonus;

    /**
     * 计算一年的总的薪水
     *
     * @return 返回总薪水值
     */
    public long calculateYearSalary() {
        return this.monthSalary * 12 + bonus;
    }

    public Salary(int monthSalary, int bonus) {
        this.monthSalary = monthSalary;
        this.bonus = bonus;
    }
}

Classfile my_examples/java/target/classes/com/dengqinghua/calculate/Salary.class
  Last modified Apr 25, 2018; size 505 bytes
  MD5 checksum 57ea37e27fa44146cdcf54c9c532799d
  Compiled from "Salary.java"
public class com.dengqinghua.calculate.Salary
  minor version: 0
  major version: 52
  flags: ACC_PUBLIC, ACC_SUPER
Constant pool:
   #1 = Fieldref           #4.#20         // com/dengqinghua/calculate/Salary.monthSalary:I
   #2 = Fieldref           #4.#21         // com/dengqinghua/calculate/Salary.bonus:I
   #3 = Methodref          #5.#22         // java/lang/Object."<init>":()V
   #4 = Class              #23            // com/dengqinghua/calculate/Salary
   #5 = Class              #24            // java/lang/Object
   #6 = Utf8               monthSalary
   #7 = Utf8               I
   #8 = Utf8               bonus
   #9 = Utf8               calculateYearSalary
  #10 = Utf8               ()J
  #11 = Utf8               Code
  #12 = Utf8               LineNumberTable
  #13 = Utf8               LocalVariableTable
  #14 = Utf8               this
  #15 = Utf8               Lcom/dengqinghua/calculate/Salary;
  #16 = Utf8               <init>
  #17 = Utf8               (II)V
  #18 = Utf8               SourceFile
  #19 = Utf8               Salary.java
  #20 = NameAndType        #6:#7          // monthSalary:I
  #21 = NameAndType        #8:#7          // bonus:I
  #22 = NameAndType        #16:#25        // "<init>":()V
  #23 = Utf8               com/dengqinghua/calculate/Salary
  #24 = Utf8               java/lang/Object
  #25 = Utf8               ()V
{
  public long calculateYearSalary();
    descriptor: ()J
    flags: ACC_PUBLIC
    Code:
      stack=2, locals=1, args_size=1
         0: aload_0
         1: getfield      #1                  // Field monthSalary:I
         4: bipush        12
         6: imul
         7: aload_0
         8: getfield      #2                  // Field bonus:I
        11: iadd
        12: i2l
        13: lreturn
      LineNumberTable:
        line 13: 0
      LocalVariableTable:
        Start  Length  Slot  Name   Signature
            0      14     0  this   Lcom/dengqinghua/calculate/Salary;

  public com.dengqinghua.calculate.Salary(int, int);
    descriptor: (II)V
    flags: ACC_PUBLIC
    Code:
      stack=2, locals=3, args_size=3
         0: aload_0
         1: invokespecial #3                  // Method java/lang/Object."<init>":()V
         4: aload_0
         5: iload_1
         6: putfield      #1                  // Field monthSalary:I
         9: aload_0
        10: iload_2
        11: putfield      #2                  // Field bonus:I
        14: return
      LineNumberTable:
        line 16: 0
        line 17: 4
        line 18: 9
        line 19: 14
      LocalVariableTable:
        Start  Length  Slot  Name   Signature
            0      15     0  this   Lcom/dengqinghua/calculate/Salary;
            0      15     1 monthSalary   I
            0      15     2 bonus   I
}
SourceFile: "Salary.java"

private int monthSalary;

Constant pool:
   #1 = Fieldref           #4.#20         // com/dengqinghua/calculate/Salary.monthSalary:I

#4  = Class              #23            // com/dengqinghua/calculate/Salary
#20 = NameAndType        #6:#7          // monthSalary:I

// u1, u2 分别代表 1个字节, 2个字节

// 字段
CONSTANT_Fieldref_info {
    u1 tag;                 // 标识她的身份属性
    u2 class_index;         // 对应的 CONSTANT_Class 的索引
    u2 name_and_type_index; // 对应的 CONSTANT_NameAndType 的索引
}

// class 或者 interface
CONSTANT_Class_info {
  u1 tag;
  u2 name_index; // 对应的 字符串 CONSTANT_Utf8 的索引
}

// 字符串的表示
CONSTANT_Utf8_info {
  u1 tag;
  u2 length;
  u1 bytes[length];
}

// 标示一个字段或者一个方法
CONSTANT_NameAndType_info {
  u1 tag;
  u2 name_index; // 对应的 字符串 CONSTANT_Utf8 的索引
  u2 descriptor_index; // 对应的描述符标示, 对应的 字符串 CONSTANT_Utf8 的索引, 如 int 用 I 表示
}

field_info {
  u2 access_flags; // 可申明多个flags, 如 public static int oneField;
  u2 name_index;
  u2 descriptor_index;
  u2 attributes_count; // attributes 的数目

  // 如果是常量, 如 final, 会存储在 attribute_info 中
  // 注意, 可变的初始化变量是不会存储在这儿的
  attribute_info attributes[attributes_count];
}

ConstantValue_attribute {
  u2 attribute_name_index;
  u4 attribute_length;
  u2 constantvalue_index;
}