鎖物件的改變

理論

在將任何資料型別作為同步鎖時，需注意的是，是否有多個執行緒同時持有鎖物件，如果同時持有相同的鎖物件，則這些執行緒之間就是同步的；

如果分別獲得鎖物件，這些執行緒之間就是非同步的。

示例

自定義共享變數類

package com.chapter02.thread2_2_16;
public class MyService {
    private String lock = "123";
    public void testMethod() {
        try {
            synchronized (lock) {
                System.
 
out.println(Thread.currentThread().getName() + " , BEGIN TIME = " + System.currentTimeMillis());
                lock = "456";
                Thread.sleep(2000);
                System.out.println(Thread.currentThread().getName() + " , END TIME = " + System.currentTimeMillis());
            }
        }
 
 catch (Exception ex) {
            ex.printStackTrace();
        }
    }
}

自定義執行緒1

package com.chapter02.thread2_2_16;
public class ThreadA extends Thread {
    private MyService service;

    public ThreadA(MyService service) {
        this.service = service;
    }

    @Override
    public void run
 
() {
        super.run();
        service.testMethod();
    }
}

自定義執行緒2

package com.chapter02.thread2_2_16;
public class ThreadB extends Thread {
    private MyService service;

    public ThreadB(MyService service) {
        this.service = service;
    }

    @Override
    public void run() {
        super.run();
        service.testMethod();
    }
}

啟動類

package com.chapter02.thread2_2_16;
public class Main1 {
    public static void main(String[] args) throws InterruptedException {
        MyService myService = new MyService();

        ThreadA a = new ThreadA(myService);
        a.setName("A");
        ThreadB b = new ThreadB(myService);
        b.setName("B");

        a.start();
        Thread.sleep(50);
        b.start();
    }
}

執行結果及結論

A , BEGIN TIME = 1541735926703
B , BEGIN TIME = 1541735926753
A , END TIME = 1541735928703
B , END TIME = 1541735928753

50毫秒過後執行緒B取得的鎖是"456"

注：只要物件不變，即使物件的屬性改變，執行結果還是同步。