併發程式設計--單例模式(飢餓模式-懶漢模式)

1. 單例模式：

- 最常見的單例模式：飢餓模式-懶漢模式；

• 1. 飢餓模式：直接例項化物件；
• 2. 懶漢模式：呼叫方法時進行例項化物件。

- 還有一種經典做法：在多執行緒模式中，一般選擇如下幾種單例模式：

• 1. dubble check instance:
• 2. static inner class:

示例：Singletion.java --> static inner class:

 1 public class Singletion {
 2 
 3     private static
 
 class InnerSingletion {
 4       private static Singletion single = new Singletion();
 5     }
 6 
 7     public static Singletion getInstance(){
 8       return InnerSingletion.single;
 9     }
10 }

示例：  dubble check instance:

 1 public class DubbleSingleton {
 2 
 3 private static DubbleSingleton ds;
 
 4 
 5     public  static DubbleSingleton getDs(){
 6       if(ds == null){
 7         try {
 8           //模擬初始化物件的準備時間...
 9           Thread.sleep(3000);
10         } catch (InterruptedException e) {
11           e.printStackTrace();
12         }
13         synchronized (DubbleSingleton.class) {
14           if
 
(ds == null){
15             ds = new DubbleSingleton();
16           }
17         }
18       }
19       return ds;
20     }
21 
22     public static void main(String[] args) {
23       Thread t1 = new Thread(new Runnable() {
24         @Override
25         public void run() {
26           System.out.println(DubbleSingleton.getDs().hashCode());
27         }
28       },"t1");
29       Thread t2 = new Thread(new Runnable() {
30         @Override
31         public void run() {
32           System.out.println(DubbleSingleton.getDs().hashCode());
33         }
34       },"t2");
35       Thread t3 = new Thread(new Runnable() {
36         @Override
37         public void run() {
38           System.out.println(DubbleSingleton.getDs().hashCode());
39         }
40       },"t3");
41 
42       t1.start();
43       t2.start();
44       t3.start();
45     }
46 }