设计模式之单例模式

1. 2种实现方法，推荐使用简单的一种。 

public class SingletonTest {/** * @param args */public static void main(String[] args) {Singleton1 singletonA = Singleton1.getSingleton1();Singleton1 singletonB = Singleton1.getSingleton1();System.out.println(singletonA == singletonB);//Singleton2 singletonC = Singleton2.getSingleton2();//Singleton2 singletonD = Singleton2.getSingleton2();//System.out.println(singletonC == singletonD);Singleton2 singletonE = Singleton2.getSingleton();Singleton2 singletonF = Singleton2.getSingleton();System.out.println(singletonE == singletonF);}}//单例模式的第一种实现class Singleton1{//静态成员变量，类加载时候new出来了。private static Singleton1 singleton = new Singleton1();//必须new出来，不能设置为空，不然多线程时候出问题。//私有构造函数private Singleton1(){}public static Singleton1 getSingleton1(){return singleton;}}//第二种实现class Singleton2{private static Singleton2 singleton;private Singleton2(){}public static Singleton2 getSingleton2(){//必须判断，加锁if(singleton == null){synchronized (Singleton2.class) {if(singleton == null){singleton = new Singleton2();}}}return singleton;}//另一种同步方式public static  synchronized Singleton2 getSingleton(){if(singleton == null){singleton = new Singleton2();}return singleton;}}