单例模式

 1 package cn.sice;
 2 
 3 public class SingleDemo
 4 {
 5 
 6     public static void main(String[] args)
 7     {
 8         Single s = Single.getInstance();
 9     }
10 
11 }
12 
13 class Single
14 {
15     private static Single sin = null;
16 
17     private Single()
18     {
19 
20     }
21 
22     public static Single getInstance()
23     {
24         if (sin == null)
25         {
26             synchronized (Single.class)
27             {
28                 if (sin == null)
29                 {
30                     sin = new Single();
31                 }
32             }
33 
34         }
35         return sin;
36     }
37 }