1. 靜態內部類(static nested class) 優先考慮
3. public class LazySingleton{
4. private LazySingleton(){}
6. private static class Nested{
7. private static final LazySingleton single = new LazySingleton();
8. }
10. public static LazySingleton getInstance(){
11. return Nested.single;
12. }
13. }

雙重檢查鎖定(DCL)

1. public class LazySingleton{
2. private LazySingleton(){}
4. private static volatile LazySingleton single = null;
6. public static LazySingleton getInstance(){
7. if(single == null){
8. synchronized (LazySingleton.class){
9. if(single == null){
10. single = new LazySingleton(); //① 非原子操作
11. }
12. }
13. }
14. return single;
15. }
16. }

單例模式實現