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