单例，懒汉模式

姜敞 7-3 11:28:42
public class Singleton {  
    private static volatile Singleton sSingleton;  
      
    private Singleton(){  
          
    }  
      
    public Singleton getInstance(){  
        if(sSingleton == null){  
            synchronized (Singleton.class) {  
                if(sSingleton == null){  
                    sSingleton = new Singleton();  
                }  
            }  
        }  
        return sSingleton;  
    }  
}  


private static volatile Singleton sSingleton 就是这个成员变量用的时候才初始化