java单例模式

1.懒汉式（单线程不安全）

class singleton{ private static singleton st; private void singleton() { } public static singleton getSingleton(){ if(st==null){ st=new singleton(); } return st; }

2多线程保证线程安全

class singleton{ private static singleton st; private void singleton() { } public static synchronized singleton getSingleton(){ if(st==null){ st=new singleton(); } return st; } }

3.饿汉式

public class Singleton { private static Singleton instance=new Singleton(); private Singleton(){ } public static Singleton getInstance(){ return instance; } }

4静态内部类

public class Singleton { private Singleton(){ } private static class SingletonHolder{ private final static Singleton instance=new Singleton(); } public static Singleton getInstance(){ return SingletonHolder.instance; } }

5同步锁

public class Singleton { private static Singleton instance=null; private Singleton(){ } public static Singleton getInstance(){ if(instance==null){ synchronized(Singleton.class){ if(instance==null){ instance=new Singleton(); } } } return instance; } }