synchronized 锁住了什么

来源：互联网发布：易途java培训编辑：程序博客网时间：2024/04/28 01:00

先上结论：

　　类方法中，synchronized锁住的是对象this,只有调用同一个对象的方法才需要获取锁。同时，同一个对象中所有加了synchronize的方法只能一次调用一个

　　静态方法中，synchronized锁的是整个类对象，类似于(X.class)，该类中所有加了synchronized的静态方法，一次只能调用一个

class Sync {    public synchronized void test() {        System.out.println("test开始..");        try {            Thread.sleep(1000);        } catch (InterruptedException e) {            e.printStackTrace();        }        System.out.println("test结束..");    }    public synchronized void test2() {        System.out.println("test2开始..");        try {            Thread.sleep(800);        } catch (InterruptedException e) {            e.printStackTrace();        }        System.out.println("test2结束..");    }}class MyThread extends Thread {    private Sync sync;    public MyThread(Sync sync) {        this.sync = sync;    }    public void run() {        sync.test();    }}class MyThread2 extends Thread {    private Sync sync;    public MyThread2(Sync sync) {        this.sync = sync;    }    public void run() {        sync.test2();    }}public class Main {    public static void main(String[] args) {        Sync sync = new Sync();        Thread thread = new MyThread(sync);        Thread thread2 = new MyThread2(sync);        thread.start();        thread2.start();    }}

运行结果:

test开始..
test结束..
test2开始..
test2结束..

方案是按顺序执行的，说明了锁住的是同一个对象:

main方法换成以下写法:

public static void main(String[] args) {        Thread thread = new MyThread(new Sync());        Thread thread2 = new MyThread2(new Sync());        thread.start();        thread2.start();}

结果:

test开始..
test2开始..
test2结束..
test结束..

synchronized没有起到同步作用，说明不是同一个锁

静态方法:

class Sync {    public static synchronized void test() {        System.out.println("test开始..");        try {            Thread.sleep(1000);        } catch (InterruptedException e) {            e.printStackTrace();        }        System.out.println("test结束..");    }    public static synchronized void test2() {        System.out.println("test2开始..");        try {            Thread.sleep(800);        } catch (InterruptedException e) {            e.printStackTrace();        }        System.out.println("test2结束..");    }}class MyThread extends Thread {    public void run() {        Sync.test();    }}class MyThread2 extends Thread {    public void run() {        Sync.test2();    }}public class Main {    public static void main(String[] args) {        Thread thread = new MyThread();        Thread thread2 = new MyThread2();        thread.start();        thread2.start();    }}

运行结果:

test开始..
test结束..
test2开始..
test2结束..

本文参考了叉叉哥的博客:Java线程同步：synchronized锁住的是代码还是对象

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