1.懒汉、线程不安全
public class Singleton { private static Singleton instance; private Singleton (){} public static Singleton getInstance() { if (instance == null) { instance = new Singleton(); } return instance; } }
2.懒汉、线程安全
public class Singleton { private static Singleton instance; private Singleton (){} public static synchronized Singleton getInstance() { if (instance == null) { instance = new Singleton(); } return instance; } }
3.饿汉
public class Singleton { private static Singleton instance = new Singleton(); private Singleton (){} public static Singleton getInstance() { return instance; } }
4.双重校验
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; } }