单例

问题描述

https://www.lintcode.com/problem/singleton/description?_from=ladder&&fromId=6

public class Singleton{
    //volatile保证了其他线程拿到的也是最新的实例
    private volatile static Singleton instance;
    //将默认的构造函数私有化，防止其他类手动new
    private Singleton(){};
    public static Singleton getInstance(){
        if(instance==null){
            synchronized(Singleton.class){
                if(instance==null){
                    instance=new Singleton();
                }
            }
        }
        return instance;
    }
}