1 class Singleton {
2
3 private Singleton() {
4 }
5
6 private static Singleton instance;
7
8 // v0.1
9 // public static Singleton getInstance(){
10 // if(instance==null) instance=new Singleton();
11 // return instance;
12 // }
13
14 // v0.2
15 // //Double-check singleton
16 // public static Singleton getInstance() {
17 // if(instance==null) {
18 // synchronized (Singleton.class) {
19 // if(instance==null) instance = new Singleton();
20 // }
21 // }
22 // return instance;
23 // }
24
25 // v0.3
26 private static class SingletonHolder{
27 static final Singleton INSTANCE=new Singleton();
28 }
29
30 public static Singleton getInstance(){
31 return SingletonHolder.INSTANCE;
32 }
33
34 }
