设计模式--单例模式

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   package com.model.danli;
   
   import java.util.ArrayList;
   
   /**
    * @Description:测试类
    * @Author: 张紫韩
    * @Crete 2021/7/2 16:40
    * 单例模式：饿汉式，懒汉式
    */
   public class DanLiMoShiDemo01 {
       public static void main(String[] args) {
           GirlFriend girlFriend = GirlFriend.getGirlFriend();
           GirlFriend girlFriend1 = GirlFriend.getGirlFriend();
           System.out.println(girlFriend1 == girlFriend);
   
           GirlFriend02 girlFriend02 = GirlFriend02.getGirlFriend02();
           GirlFriend02 girlFriend03 = GirlFriend02.getGirlFriend02();
           System.out.println(girlFriend03==girlFriend02);
   
   
   
   
   
       }
   }
   //饿汉式
   class GirlFriend{
       private String name;
       private int age;
   
       /**
        * 1.构造器私有化
        * 2.在类的内部直接创建对象
        * 3.提供一个公共的static的方法，返回类的对象
        *  在类加载的时候创建单例模式对象
        * */
       private static GirlFriend girlFriend=new GirlFriend();
       private GirlFriend() { }
   
       public String getName() {
           return name;
       }
   
       public void setName(String name) {
           this.name = name;
       }
   
       public int getAge() {
           return age;
       }
   
       public void setAge(int age) {
           this.age = age;
       }
   
       public static GirlFriend getGirlFriend() {
           return girlFriend;
       }
   
       @Override
       public String toString() {
           return "GirlFriend{" +
                   "name='" + name + '\'' +
                   ", age=" + age +
                   '}';
       }
   }
   class GirlFriend02{
       /**
        * 1.构造器私有化
        * 2.定义一个static修斯的类对象
        * 3.提供一个static修饰的public方法，返回这个类对象
        * 4.提供的public方法，判断是否已经创建过对象，如果创建过就返回上次创建的类对象，从而保证单例模式
        * */
       private String name;
       private int age;
       private static volatile GirlFriend02 girlFriend02;
   
       private GirlFriend02(){ }
       public static GirlFriend02 getGirlFriend02(){
           if (girlFriend02==null){
               synchronized (GirlFriend02.class){
                   if (girlFriend02==null){
                       girlFriend02=new GirlFriend02();
                   }
               }
           }
           return girlFriend02;
       }
   //    单例线程模式下可以，多线程时无法保证单例
   //    public static GirlFriend02 getGirlFriend02(){
   //                if (girlFriend02==null){
   //                    girlFriend02=new GirlFriend02();
   //                }
   //        return girlFriend02;
   //        }
   
   
       public String getName() {
           return name;
       }
   
       public void setName(String name) {
           this.name = name;
       }
   
       public int getAge() {
           return age;
       }
   
       public void setAge(int age) {
           this.age = age;
       }
   
       @Override
       public String toString() {
           return "GirlFriend02{" +
                   "name='" + name + '\'' +
                   ", age=" + age +
                   '}';
       }
   }