一张图讲解对象锁和关键字synchronized修饰方法(代码块)

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目录(?)[+]

每个对象在出生的时候就有一把钥匙（监视器Monitor），那么被synchronized 修饰的方法相当于给方法加了一个锁，这个方法就可以进行同步，在多线程的时候，不会出现线程安全问题。

注：Monitor是 Java中用以实现线程之间的互斥与协作的主要手段，它可以看成是对象或者 Class的锁。每一个对象都有，也仅有一个 Monitor。

下面通过一张图片进行讲解：

1.一张图片

图片看不清，请点击这里：高清大图

这里写图片描述

2.图片对应的代码

import java.util.Date;/** * 测试的object类 * * @author:dufy * @version:1.0.0 * @date 2017/9/29 * @email 742981086@qq.com */public class ObjectTest {    public synchronized  void methodA(){        try {            System.out.println("This is methodA ...." + Thread.currentThread().getName() + ": " + new Date());            Thread.sleep(1000);        } catch (InterruptedException e) {            e.printStackTrace();        }    }    public void methodB(){        System.out.println("This is methodB ...." + Thread.currentThread().getName() + ": " + new Date());    }    public synchronized void methodC(){        try {            System.out.println("This is methodC ...." + Thread.currentThread().getName() + ": " + new Date());            Thread.sleep(3000);        } catch (InterruptedException e) {            e.printStackTrace();        }    }}1
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package com.dufy.concurrentcode;/** * 测试线程类 * * @author:dufy * @version:1.0.0 * @date 2017/9/29 * @email 742981086@qq.com */public class ThreadTest extends Thread{    public static void main(String[] args) {        ObjectTest ot = new ObjectTest();        Thread1 t1 = new Thread1(ot,"thread1");        Thread2 t2 = new Thread2(ot,"thread2");        Thread3 t3 = new Thread3(ot,"thread3");        Thread4 t4 = new Thread4(ot,"thread4");        t1.start();        t2.start();        t3.start();        t4.start();    }    static class Thread1 extends Thread{        private ObjectTest objectTest;        public Thread1(ObjectTest objectTest,String name){            setName(name);            this.objectTest = objectTest;        }        @Override        public void run() {            super.run();            objectTest.methodA();        }    }    static class Thread2 extends Thread{        private ObjectTest objectTest;        public Thread2(ObjectTest objectTest,String name){            setName(name);            this.objectTest = objectTest;        }        @Override        public void run() {            super.run();            objectTest.methodB();        }    }    static class Thread3 extends Thread{        private ObjectTest objectTest;        public Thread3(ObjectTest objectTest,String name){            setName(name);            this.objectTest = objectTest;        }        @Override        public void run() {            super.run();            objectTest.methodA();        }    }    static class Thread4 extends Thread{        private ObjectTest objectTest;        public Thread4(ObjectTest objectTest,String name){            setName(name);            this.objectTest = objectTest;        }        @Override        public void run() {            super.run();            objectTest.methodC();        }    }}1
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运行结果：

This is methodB ....thread2: Fri Sep 29 23:21:17 CST 2017This is methodA ....thread1: Fri Sep 29 23:21:17 CST 2017This is methodC ....thread4: Fri Sep 29 23:21:18 CST 2017This is methodA ....thread3: Fri Sep 29 23:21:21 CST 2017

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