Singleton

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.

In Java:

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

a should equal to b.

Challenge

If we call getInstance concurrently, can you make sure your code could run correctly?

 

class Solution {
    /**
     * @return: The same instance of this class every time
     /*Singleton类定义一个GetInstance()操作，允许客户访问它的唯一实例。GetInstance()是一个静态方法，主要负责创建自己的唯一实例。*/  */
    private static Solution singleton;
    //构造方法让其private，这就堵死了外界利用new创建此类实例的可能//  
    private Solution(){};

     /*此方法是获得本类实例的唯一全局访问点。*/  
    public static Solution getInstance() {
        // /*若实例不存在，则new一个新实例，否则返回已有实例*/  
        if(singleton==null) 
        {
            singleton=new Solution();
        }
        
        return singleton;
    }
};