设计模式——“signleton”

那天别人问了我一个问题，关于单例模式的，由于之前了解的都是蜻蜓点水，所以重新复习了一次重新总结。

单例模式的写法总的来说有5种：懒汉，恶汉，枚举，双重校验锁，静态内部类

懒汉

public class Signleton{     
        private static Signleton instance;     
        private Signleton(){}      
        public static synchronized Sginleton getInstance(){      
             if( instance == null ){     
                instance = new Signleton();      
             }      
             return instance;      
        }    
}

恶汉:

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

双重校验锁：

public class Singleton {     
            private volatile static Singleton singleton;     
            private Singleton (){}      
            public static Singleton getSingleton() {     
                if (singleton == null) {     
                      synchronized (Singleton.class) {     
                          if (singleton == null) {     
                              singleton = new Singleton();     
                          }    
                      } 
                }            
                return singleton;            
            }    
    }  

枚举：

public enum Singleton {     
        INSTANCE;            
        public void whateverMethod() {}     
    }

静态内部类：

public class Singleton {          
        private static class SingletonHolder {        
           private static final Singleton INSTANCE = new Singleton();          
        }             
        private Singleton (){}           
        public static final Singleton getInstance() {                 
            return SingletonHolder.INSTANCE;             
        }         
}  

有兴趣的可以看这篇文章: http://stackoverflow.com/questions/70689/what-is-an-efficient-way-to-implement-a-singleton-pattern-in-java
the best way to do it is to use：
Since java5 ： enum: 
Pre    java5 ：other