单例、工厂、适配器、装饰器

 1 public class Singleton {
 2     
 3     
 4     //饿汉加载
 5     //应用时才加载，节省内存
 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     //饿汉加载 
22     //浪费内存
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 }