懒汉式实现单例模式

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package thread;/** * 懒汉式实现单例模式 * 1、创建一个静态变量 * 2、构造方法私有化 * 3、创建一个静态方法获取实例对象，如果对象为空则创建对象 * @author Administrator * */public class Singleton {private static Singleton singleton = null;private Singleton(){}//线程安全且高效public static Singleton getInstance(){if(singleton == null){synchronized (Singleton.class) {if(singleton == null){singleton = new Singleton();}}}return singleton;}//线程安全，不高效public static Singleton getInstance3(){synchronized (Singleton.class) {if(singleton == null){singleton = new Singleton();}return singleton;}}//线程安全，不高效public static synchronized Singleton getInstance2(){if(singleton == null){singleton = new Singleton();}return singleton;}//线程不安全public static Singleton getInstance1(){if(singleton == null){singleton = new Singleton();}return singleton;}}

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