当我们想实例化一个类，并可以一直使用这个类，可以使用单例模式：

方式一：

1 package com.kunhong.design.test; 2  3 public class Singleton { 4     private static Singleton instance = new Singleton(); 5      6     private Singleton() { 7  8     } 9 10     public static Singleton getInstance() {11         return instance;12     }13 }

方法二：

1 package com.kunhong.design.test; 2  3 public class Singleton { 4     private static Singleton instance = null; 5      6     private Singleton() { 7  8     } 9     public synchronized static Singleton getInstance(){10         if(instance == null){11             instance = new Singleton();12         }13         return instance;14     }15 }