单例模式

最新推荐文章于 2025-05-23 19:33:43 发布

weixin_30823683

最新推荐文章于 2025-05-23 19:33:43 发布

阅读量64

点赞数

CC 4.0 BY-SA版权

原文链接：http://www.cnblogs.com/bobi1234/p/7631657.html

本文详细介绍了单例模式的两种主要实现方式：饿汉式和懒汉式，并针对懒汉式存在的线程安全问题提供了三种解决方案。

单例模式分类

/**
 * Author：Mr.X
 * Date：2017/9/20 11:44
 * Description：
 *
 * @1、单例模式的目的：始终保持只有一个对象
 * @2、单例模式分为：饿汉式、懒汉式、登记式(可忽略)
 */
public class SingletonTest implements Runnable {

    @Override
    public void run() {

        try {
            Thread.sleep(2000);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        System.out.println(Thread.currentThread().getName() + "---->" + Singleton1.getInstance());
        System.out.println(Thread.currentThread().getName() + "---->" + Singleton2.getInstance());
    }

    public static void main(String[] args) {
        for (int i = 0; i < 10; i++) {
            new Thread(new SingletonTest()).start();
        }
    }
}

/**
 * @饿汉式单例：线程安全
 */
class Singleton1 {

    private Singleton1() {
    }

    private static final Singleton1 singleton1 = new Singleton1();

    public static Singleton1 getInstance() {
        return singleton1;
    }
}

/**
 * @懒汉式单例：线程不安全
 */
class Singleton2 {

    private Singleton2() {
    }

    public static Singleton2 singleton2 = null;

    public static Singleton2 getInstance() {
        if (singleton2 == null) {
            singleton2 = new Singleton2();
        }
        return singleton2;
    }
}

让单例模式线程安全的3种方法

/**
 * Author：Mr.X
 * Date：2017/9/20 14:13
 * Description：
 * @、本例中：专门解决懒汉式的线程安全问题，分别有3中解决方案！
 */
public class SingletonTest implements Runnable {

    @Override
    public void run() {
        try {
            Thread.sleep(2000);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        //System.out.println(Thread.currentThread().getName() + "-->" + Singleton1.getInstance());
        //System.out.println(Thread.currentThread().getName() + "-->" + Singleton2.getInstance());
        System.out.println(Thread.currentThread().getName() + "-->" + Singleton3.getInstance());
    }

    public static void main(String[] args) {
        for (int i = 0; i < 10; i++) {
            new Thread(new SingletonTest()).start();
        }
    }
}

class Singleton1 {

    private Singleton1() {
    }

    public static Singleton1 singleton = null;

    public static synchronized Singleton1 getInstance() {
        if (singleton != null) {
            singleton = new Singleton1();
        }
        return singleton;
    }
}

class Singleton2 {

    private Singleton2() {
    }

    public static Singleton2 singleton = null;

    public static Singleton2 getInstance() {
        if (singleton == null) {
            synchronized (Singleton2.class) {
                if (singleton != null) {
                    singleton = new Singleton2();
                }
            }
        }
        return singleton;
    }
}

class Singleton3 {

    private Singleton3() {
    }

    private static class LazyHolder {
        private static final Singleton3 INSTANCE = new Singleton3();
    }

    public static final Singleton3 getInstance() {
        return LazyHolder.INSTANCE;
    }
}

转载于:https://www.cnblogs.com/bobi1234/p/7631657.html