设计模式（一）：单例模式

 1 package com.cllover.lazy;
 2 
 3 public class LazySingleton {
 4     public static void main(String[] args) {
 5 
 6             lazyinstance instance = lazyinstance.getInstance();
 7             System.out.println(instance+"\n");
 8             lazyinstance instance1 = lazyinstance.getInstance();
 9             System.out.println(instance1+"\n");
10 
11 
12     }
13 }
14 
15 
16 class lazyinstance{
17 
18     private static lazyinstance instance;
19 
20     private lazyinstance(){
21     }
22 
23     public  static lazyinstance getInstance() {
24         if (instance == null){
25           instance = new lazyinstance();
26         }
27         return instance;
28     }
29 }

 1 package com.cllover.lazy;
 2 
 3 public class LazySingleton {
 4 
 5     public static void main(String[] args) {
 6         //线程一
 7         new Thread(()->{
 8             lazyinstance instance  = lazyinstance.getInstance();
 9             System.out.println(instance+"\n");
10         }).start();
11         //线程二
12         new Thread(()->{
13             lazyinstance instance1  = lazyinstance.getInstance();
14             System.out.println(instance1+"\n");
15         }).start();
16     }
17 }
18 class lazyinstance{
19 
20     private static lazyinstance instance;
21 
22     private lazyinstance(){
23     }
24 
25     public  static lazyinstance getInstance() {
26 
27         if (instance == null){
28           instance = new lazyinstance();
29         }
30         return instance;
31     }
32 }

 1 package com.cllover.lazy;
 2 
 3 public class LazySingleton {
 4 
 5     public static void main(String[] args) {
 6         //线程一
 7         new Thread(()->{
 8             lazyinstance instance  = lazyinstance.getInstance();
 9             System.out.println(instance+"\n");
10         }).start();
11         //线程二
12         new Thread(()->{
13             lazyinstance instance1  = lazyinstance.getInstance();
14             System.out.println(instance1+"\n");
15         }).start();
16         //线程三
17         new Thread(()->{
18             lazyinstance instance2  = lazyinstance.getInstance();
19             System.out.println(instance2+"\n");
20         }).start();
21     }
22 }
23 class lazyinstance{
24 
25     private static lazyinstance instance;
26 
27     private lazyinstance(){
28     }
29 
30     public  static lazyinstance getInstance() {
31 
32         if (instance == null){
33             //同步堵塞
34             synchronized (lazyinstance.class){
35                 //是否进行过实例化
36                 if (instance == null){
37                     instance = new lazyinstance();
38                 }
39             }
40         }
41         return instance;
42     }
43 }