package com.yanwu.www.demo;/** 测试单例模式* * 饿汉模式* * @author harvey* */public class SingletonDemo1 {//类初始化时立即加载对象(没有延迟加载的优势)，天然的线程安全private static SingletonDemo1 instance=new SingletonDemo1(); //构造器私有化private  SingletonDemo1(){}//方法没有同步，调用效率高public static SingletonDemo1 getInstance(){return instance;}}

package com.yanwu.www.demo;/**测试单例模式**懒汉模式**@author harvey* */public class SingletonDemo2 {//类初始化时，不初始化这个对象(延时加载，真正用的时候再创建)private static SingletonDemo2 instance;//构造器私有化private SingletonDemo2(){}//方法同步，调用效率低public static synchronized SingletonDemo2 getInstance(){if(instance==null){instance=new SingletonDemo2();}return instance;}}

package com.yanwu.www.demo;/** 单例模式* * 双重检测锁式* * 由于JVM底层内部模型原型，偶尔会出现问题，不建议使用* * @author harvey*/public class SingletonDemo5 {private volatile static SingletonDemo5 SingletonDemo5;private SingletonDemo5() {}public static SingletonDemo5 newInstance() {if (SingletonDemo5 == null) {synchronized (SingletonDemo5.class) {if (SingletonDemo5 == null) {SingletonDemo5 = new SingletonDemo5();}}}return SingletonDemo5;}}

package com.yanwu.www.demo;/** 单例模式* * 静态内部类的实现* * 1.外部类没有static 属性，不会像饿汉一样立即加载对象* * 2.只有真正调用getInstance()才会加载静态内部类，加载时是线程安全的* * 3.兼并延时调用和并发高效调用* * @author harvey* */public class SingletonDemo3 {private static class SingletonClassInstance{private static final SingletonDemo3 instance=new SingletonDemo3();}private SingletonDemo3(){}public static SingletonDemo3 getInstance(){return SingletonClassInstance.instance;}}

package com.yanwu.www.demo;/** 单例模式* * 枚举式实现* * 1.避免了反射和反序列化的漏洞* * 2.没有延时加载的效果* * @author harvey*/public enum SingletonDemo4 {//枚举元素本身就是单例INSTANCE;//添加自己需要的操作public void singletonOperation(){}}