设计模式 -- 单例模式

来源：互联网发布：s函数可以用c语言写吗编辑：程序博客网时间：2024/05/29 14:05

参考：http://www.runoob.com/design-pattern/singleton-pattern.html
这里写图片描述
源码下载：https://github.com/gpqhl0071/pattern.git
1. 对象在整个工程的运行周期内，值创建一个对象

代码

/**Copyright (c) 2016, gp.inc and/or its affiliates. All rights reserved.*/package com.pattern.single;public class SingleObject {    // 创建 SingleObject 的一个对象    private static SingleObject instance = new SingleObject();    // 让构造函数为 private，这样该类就不会被实例化    private SingleObject() {    }    // 获取唯一可用的对象    public static SingleObject getInstance() {        return instance;    }    public void showMessage() {        System.out.println("Hello World!");    }}

/**Copyright (c) 2016, gp.inc and/or its affiliates. All rights reserved.*/package com.pattern.single.test;import com.pattern.single.SingleObject;public class SingletonPatternDemo {    public static void main(String[] args) {        // 不合法的构造函数        // 编译时错误：构造函数 SingleObject() 是不可见的        // SingleObject object = new SingleObject();        // 获取唯一可用的对象        SingleObject object = SingleObject.getInstance();        // 显示消息        object.showMessage();    }}

结果：

Hello World!

6中单例的实现，代码如下：

/**Copyright (c) 2016, gp.inc and/or its affiliates. All rights reserved.*/package com.pattern.single;/** * 懒汉式，线程不安全 * @author: gao peng * @date:   2016年3月3日 上午11:33:16    * */public class Singleton1 {    private static Singleton1 instance;    private Singleton1() {    }    public static Singleton1 getInstance() {        if (instance == null) {            instance = new Singleton1();        }        return instance;    }}

/**Copyright (c) 2016, gp.inc and/or its affiliates. All rights reserved.*/package com.pattern.single;/** * 懒汉式，线程安全 * @author: gao peng * @date:   2016年3月3日 上午11:34:11    * */public class Singleton2 {    private static Singleton2 instance;    private Singleton2 (){}    public static synchronized Singleton2 getInstance() {        if (instance == null) {            instance = new Singleton2();        }        return instance;    }}

/**Copyright (c) 2016, gp.inc and/or its affiliates. All rights reserved.*/package com.pattern.single;/** * 饿汉式 * @author: gao peng * @date:   2016年3月3日 上午11:34:39    * */public class Singleton3 {    private static Singleton3 instance = new Singleton3();    private Singleton3() {    }    public static Singleton3 getInstance() {        return instance;    }}

/**Copyright (c) 2016, gp.inc and/or its affiliates. All rights reserved.*/package com.pattern.single;/** * 双检锁/双重校验锁（DCL，即 double-checked locking） * @author: gao peng * @date:   2016年3月3日 上午11:35:21    * */public class Singleton4 {    private volatile static Singleton4 Singleton4;    private Singleton4() {    }    public static Singleton4 getSingleton4() {        if (Singleton4 == null) {            synchronized (Singleton4.class) {                if (Singleton4 == null) {                    Singleton4 = new Singleton4();                }            }        }        return Singleton4;    }}

/**Copyright (c) 2016, gp.inc and/or its affiliates. All rights reserved.*/package com.pattern.single;/** * 登记式/静态内部类 * @author: gao peng * @date:   2016年3月3日 上午11:36:20    * */public class Singleton5 {    private static class Singleton5Holder {        private static final Singleton5 INSTANCE = new Singleton5();    }    private Singleton5() {    }    public static final Singleton5 getInstance() {        return Singleton5Holder.INSTANCE;    }}

/**Copyright (c) 2016, gp.inc and/or its affiliates. All rights reserved.*/package com.pattern.single;/** * 枚举 * @author: gao peng * @date:   2016年3月3日 上午11:37:07    * */public enum Singleton6 {    INSTANCE;      public void whateverMethod() {      } }

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