public class MyService {    private String lock = "123";    public void testMethod() {        synchronized (lock) {            System.out.println(ThreadB.currentThread().getName() + "begin " + System.currentTimeMillis());            lock="456";            try {                ThreadB.sleep(2000);                System.out.println(ThreadB.currentThread().getName() + "end " + System.currentTimeMillis());                            } catch (InterruptedException e) {                // TODO Auto-generated catch block                e.printStackTrace();            }        }    }    }

锁lock从“123” 改为“456”

ThreadA和ThreadB

public class ThreadA extends Thread {    private MyService myService;    public ThreadA(MyService myService) {        this.myService = myService;    }    public void run() {        myService.testMethod();    }}public class ThreadB extends Thread {    private MyService myService;    public ThreadB(MyService myService) {        this.myService = myService;    }    public void run() {        myService.testMethod();    }}

Run

public class Run {    public static void main(String[] args) throws InterruptedException {        MyService myService = new MyService();                ThreadA threadA= new ThreadA(myService);        threadA.start();        Thread.sleep(50);        ThreadA threadB= new ThreadA(myService);        threadB.start();            }        }

如果将Thread.sleep(50) 注释掉，A和B获取的锁都是“123”，虽然将锁改为“456”，结果还是同步的。