java单例模式小结

1. 双检索实现的单例，是线程安全的。

public class Singleleton {   
   private Singleleton() {}   
   private static Singleleton instance = null;   
   public static Singleleton getInstance() {   
      if(instance == null){    
         synchronize(Singleleton.class){   
            if(instance == null){   
               instance = new Singleton();   
            }   
         }   
      }   
      return instance;   
   }   
}  

2. 枚举类型实现的单例，目前比较推荐