单例模式

 1 package com.singlePattern.obj;
 2 
 3 /**
 4  * @program: designPattern
 5  * @description: 单例对象
 6  * @author: Mr.Yang
 7  * @create: 2018-11-24 21:00
 8  **/
 9 public class Singleton {
10     private static Singleton singleton;
11 
12     private Singleton(){}
13 
14     public static synchronized Singleton getInstance(){
15         if(singleton==null){
16             singleton=new Singleton();
17         }
18         return singleton;
19     }
20 }

 1 package com.singlePattern.obj;
 2 
 3 /**
 4  * @program: designPattern
 5  * @description: 单例对象
 6  * @author: Mr.Yang
 7  * @create: 2018-11-24 21:00
 8  **/
 9 public class Singleton {
10     private static Singleton singleton = new Singleton();
11 
12     private Singleton(){}
13 
14     public static  Singleton getInstance(){
15         return singleton;
16     }
17 }

 1 package com.singlePattern.obj;
 2 
 3 /**
 4  * @program: designPattern
 5  * @description: 单例对象
 6  * @author: Mr.Yang
 7  * @create: 2018-11-24 21:00
 8  **/
 9 public class Singleton {
10    /* private static Singleton singleton = new Singleton();
11 
12     private Singleton(){}
13 
14     public static  Singleton getInstance(){
15         return singleton;
16     }*/
17 
18     //volatile关键词保证，当singleton变量被初始化成对象实例时，多个线程正确的处理该变量
19     private volatile static Singleton singleton;
20 
21     private Singleton() {
22     }
23 
24     /**
25      * 这种方式保证只有第一次创建实例的时候，才能彻底走完这个方法
26      * 双重检查加锁在1.4或者更早的jdva版本中，jvm对于volatile关键字的实现会导致双重检查加锁
27      * 的实现。建议这个版本中的不要使用这个设计模式。
28      *
29      * @return
30      */
31     public static Singleton getInstance() {
32         if (singleton == null) {
33             synchronized (Singleton.class) {
34                 if (singleton == null) {
35                     singleton = new Singleton();
36                 }
37             }
38         }
39         return singleton;
40     }
41 }