标签：四种 volatile log hold style div 线程 new ret
第一种（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; } }
第二种（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; } }
第三种（饿汉）：
public class Singleton { private static Singleton instance = new Singleton(); private Singleton (){} public static Singleton getInstance() { return instance; } }
第四种（饿汉，变种）：
private static Singleton instance = null; static { instance = new Singleton(); } private Singleton (){} public static Singleton getInstance() { return instance; } }
第五种（静态内部类）：
public class Singleton { private static class SingletonHolder { private static final Singleton INSTANCE = new Singleton(); } private Singleton (){} public static final Singleton getInstance() { return SingletonHolder.INSTANCE; } }
第六种（枚举）：
public enum Singleton { INSTANCE; public void whateverMethod() { } }
第七种（双重校验锁）：
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; } }
标签：四种 volatile log hold style div 线程 new ret
原文地址：http://www.cnblogs.com/greatfish/p/6021516.html
