项目中经常会用到单例模式，这里总结一下
1饿汉式
public class Singleton { //饿汉式 private Singleton(){ } private static Singleton singleton = new Singleton(); public static Singleton getInstance(){ return singleton; } }
2懒汉式 线程安全的
public class Singleton { //懒汉式 private Singleton(){ } private static Singleton singleton = null; public static synchronized Singleton getInstance(){ if(singleton==null){ return new Singleton(); } return singleton; } }
3双中校验 线程安全的
public class Singleton { //双重校验 private Singleton(){ } private static volatile Singleton singleton = null; public static Singleton getInstance(){ if(singleton==null){ synchronized(Singleton.class){ if (singleton==null) { return new Singleton(); } } } return singleton; } }
4静态内部类也就是嵌套类 线程安全的
public class Singleton { private Singleton(){} private static class InstanceHolder{ private static Singleton singleton = new Singleton(); } public static Singleton getInstance(){ return InstanceHolder.singleton; } }
synchronized会影响服务性能，为什么会影响，不太清楚，以后懂了在补充。静态内部类（嵌套类）相比之下会好些
原文：http://www.cnblogs.com/chenzhibo/p/5131578.html