初学单例模式，写的是这种，最简单的懒汉模式
public class Singleton { private static Singleton instance; private Singleton (){} public static Singleton getInstance() { if (instance == null) { instance = new Singleton(); } return instance; } }
后来面试，觉得一直加一种
public class Singleton { private static Singleton instance; private Singleton (){} public static synchronized Singleton getInstance() { if (instance == null) { instance = new Singleton(); } return instance; } } 觉得自己写的老牛逼了。
其实深入来说只有双重校验才能真正的单例模式
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; } }
