204. Singleton

Description

Singleton is a most widely used design pattern. If a class has and only has one instance at every moment, we call this design as singleton. For example, for class Mouse (not a animal mouse), we should design it in singleton.

You job is to implement a getInstance method for given class, return the same instance of this class every time you call this method.

Example

In Java:

A a = A.getInstance();
A b = A.getInstance();

a should equal to b.

解题：单例模式是最常用的设计模式，如何实现这样的功能，每次调用getInstance函数，返回同一个引用。既然所有的对象调用时，返回同一个引用，那么就把它定义为Static，为所有对象共享，也只有定义为static才可以放进static函数里。代码如下：

 class Solution {
     /**
      * @return: The same instance of this class every time
      */
     private static Solution instance = null;
     public static Solution getInstance() {
         // write your code here
         if(instance == null)
              instance = new Solution();
         return instance;
     }
 }