單例模式160905

 1 /**
 2  * 單例模式:保證只有一個實例 private Singleton(){};
 3  * 餓漢式:先建立 private static final Singleton INSTANCE = new Singleton(); 用的時候調用 public static Singleton getInstance(){return INSTANCE;}
 4  * 懶漢式:用的時候建立實例。
 5  *         synchronized在方法內,則主要double-check;
 6  *         同步在方法上 public static synchronized Singleton getInstance(){ if(instanceLazy==null) instanceLazy=new Singleton();return instanceLazy;}
 7  * 靜態代碼塊:
 8  *         static{ instanceStaticBlock = new Singleton();}
 9  * 靜態內部類:
10  *         private static class SingletonHolder{ public static final INSTANCE_STATIC_CLASS=new Singleton();}
11  * 枚舉:
12  *         public enum SingletonEnum{INSTANCE;}
13  */
14 public class Singleton implements Serializable{
15     private Singleton(){};  // 私有化構造方法,外部沒法建立本類 
16     // 餓漢式
17     private static final Singleton INSTANCE = new Singleton();
18     public static Singleton getInstanceEager(){ return INSTANCE; }
19     // 懶漢式
20     private static volatile Singleton instanceLazy = null;
21     public static Singleton getInstanceLazy1(){
22         if(instanceLazy == null){
23             synchronized(Singleton.class){
24                 if(instanceLazy == null){
25                     instanceLazy = new Singleton();
26                 }
27             }
28         }
29         return instanceLazy;
30     }
31     public static synchronized Singleton getInstanceLazy2(){
32         if(instanceLazy == null){
33             instanceLazy = new Singleton();
34         }
35         return instanceLazy;
36     }
37     // 靜態代碼塊
38     private static Singleton instanceStaticBlock = null;
39     static{
40         instanceStaticBlock = new Singleton();
41     }
42     public static Singleton getInstanceStaticBlock(){ return instanceStaticBlock; }
43     // 靜態內部類
44     private static class SingletonHolder{ public static final Singleton INSTANCE = new Singleton(); }
45     public static Singleton getInstanceStaticClass(){ return SingletonHolder.INSTANCE; }
46     
47     // 磚家建議:功能完善,性能更佳,不存在序列化等問題的單例 就是 靜態內部類 + 以下的代碼
48     private static final long serialVersionUID = 1L;
49     protected Object readResolve(){ return getInstanceStaticClass(); }
50 }
51 //枚舉
52 enum SingletonEnum{
53     INSTANCE;
54 }