單例

單例分為懶漢式和餓漢式

 1 public class Singleton {
 2     
 3     
 4     //餓漢加載
 5     //應用時才加載，節省內存
 6     private static Singleton instance;   
 7     private Singleton() {  
 8     }  
 9     public static Singleton getInstance(){  
10         if (instance == null) {  
11             synchronized
 
 (Singleton.class) {  
12                 if (instance == null) {  
13                     instance = new Singleton();  
14                 }  
15             }  
16         }  
17         return instance;  
18     } 
19     
20     
21     //餓漢加載 
22     //浪費內存
23 //    private static Singleton singleton=new Singleton();
 
24 //    public static Singleton getInstance(){
25 //        return singleton;
26 //    }
27     
28     public void run(){
29         System.out.println("hellowolrd");
30     }
31 }

工廠模式：

單例、工廠、適配器、裝飾器