单例几种常见的模式

单例几种常见的形式

原文地址：http://forestqqqq.iteye.com/blog/1896723

一，饿汉式单例

1. //饿汉式单例1??
2. public?class?Singleton1?{??
3. ????private?static?final?Singleton1?instance?=?new?Singleton1();??
4. ????private?Singleton1(){}??
5. ????public?static?Singleton1?getInstance(){??
6. ????????return?instance;??
7. ????}??
8. }??
9. ??
10. //饿汉式单例2??
11. class?Singleton{??
12. ????private?static?class?Single{??
13. ????????static?final?Singleton?instance?=?new?Singleton();??
14. ????}??
15. ????private?Singleton(){}??
16. ????public?static?Singleton?getInstance(){??
17. ????????return?Single.instance;??
18. ????}??
19. }??

?

二，懒汉式单例

1. //懒汉式单例??
2. public?class?Singleton2?{??
3. ????private?static?Singleton2?instance?=?null;??
4. ????private?Singleton2(){}??
5. ????public?static?synchronized?Singleton2?getInstance(){??
6. ????????if(instance?==?null){??
7. ????????????instance?=?new?Singleton2();??
8. ????????}??
9. ????????return?instance;??
10. ????}??
11. }??

?

三，DCL双重锁检测式单例

1. //DCL双重锁检测式单例??
2. public?class?Singleton3?{??
3. ????private?volatile?static?Singleton3?instance?=?null;??
4. ????private?Singleton3(){}??
5. ????public?static?Singleton3?getInstance(){??
6. ????????if(instance?==?null){??
7. ????????????synchronized(Singleton3.class){??
8. ????????????????if(instance?==?null){??
9. ????????????????????instance?=?new?Singleton3();??
10. ????????????????}??
11. ????????????}??
12. ????????}??
13. ????????return?instance;??
14. ????}??
15. //参考文章：http://www.ibm.com/developerworks/cn/java/j-dcl.html??
16. }??

?

?

四，登记式单例

1. import?java.lang.reflect.Constructor;??
2. import?java.util.HashMap;??
3. import?java.util.Map;??
4. ??
5. //登记式单例??
6. public?class?Singleton4?{??
7. ????private??static?final?Map<String,Singleton4>?instances?=??
8. ????????????new?HashMap<String,Singleton4>();??
9. ????static{??
10. ????????Singleton4?instance?=?new?Singleton4();??
11. ????????instances.put(instance.getClass().getName(),?instance);??
12. ????}??
13. ????protected?Singleton4(){}??
14. ????public?static?synchronized?Singleton4?getInstance(String?name){??
15. ????????if(name?==?null){??
16. ????????????name?=?Singleton4.class.getName();??
17. ????????}??
18. ????????if(instances.get(name)?==?null){??
19. ????????????try?{??
20. ????????????????Constructor?con?=?Class.forName(name).getDeclaredConstructor();??
21. ????????????????con.setAccessible(true);??
22. ????????????????instances.put(name,?(Singleton4)con.newInstance());??
23. ????????????}?catch?(Exception?e)?{??
24. ????????????????e.printStackTrace();??
25. ????????????}??
26. ????????}??
27. ????????return?instances.get(name);??
28. ????}??
29. //参考文章：http://www.cnblogs.com/whgw/archive/2011/10/05/2199535.html??
30. }??