Singleton,了解一下

最新推荐文章于 2021-06-23 16:50:32 发布

原创最新推荐文章于 2021-06-23 16:50:32 发布 · 160 阅读

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本文介绍了一种使用四种不同同步机制实现单例模式的方法。通过静态内部类的方式，在Java中创建线程安全且懒加载的单例对象。这些方法包括基本的同步块、显式锁、synchronized关键字以及利用ReentrantLock。

package suanfa;

import java.util.concurrent.locks.ReentrantLock;

public class MySingleton {
    static class S1 {
        private static S1 instance;
        private S1() {
        }


        public static S1 getInstance() {
            if (instance == null) {
                instance = new S1();
            }
            return instance;
        }
    }

    static class S2 {
        private static S2 instance;
        public S2() {
        }
        public static synchronized S2 getInstance() {
            if (instance == null) {
                instance = new S2();

            }
            return instance;
        }
    }


    static class S3 {
        private static S3 instance;
        private static byte[] lock  = new byte[0];
        private S3() {
        }

        public static S3 getInstance() {
            if (instance == null) {
                synchronized (lock) {
                    if (instance == null) {
                        instance = new S3();
                    }

                }
            }
            return instance;
        }
    }


    static class S4 {
        private static S4 instance; 
        private static ReentrantLock lock = new ReentrantLock();
        private S4() {
        }

        public static S4 getInstance() {
            if (instance == null) {
                lock.lock();
                if (instance==null) {
                    instance = new S4();
                }
                lock.unlock();
            }
            return instance;
        }
    }


}