在Java中同步两个线程

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我的java程序中有两个线程,一个是主线程,另一个是在主线程中生成的线程A.现在,我希望主线程启动线程A并等待,直到线程A在run方法中执行了部分代码,线程A应该挂起它自己.然后,主线程应该开始运行,运行几行代码,然后线程A应该再次从停止的地方开始,反之亦然.这应该发生n次.
我正在尝试如下：

线程A类：

public class ThreadA implements Runnable {
    boolean suspended = false;
    boolean stopped = false;
    synchronized void stop() {
        stopped = true;
        suspended = false;
        notify();
    }
    synchronized void suspend() {
        suspended = true;
    }
    synchronized void resume() {
        suspended = false;
        notify();
    }
    void job() throws InterruptedException {
        for (int i = 0; i < 5; i++)
            synchronized (this) {
                System.out.println("performing job.");
                suspend();
                while (suspended) {
                    notify();
                    suspended = false;
                }
            }
    }
    @Override
    public void run() {
        try {
            job();
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
    }
}

主线程：

public class MainThread {
    public static void main(String[] args) throws InterruptedException {
        ThreadA a1=new ThreadA();
        Thread t1=new Thread(a1);
        synchronized (t1) {
            t1.start();
            for (int i = 0; i < 5; i++) {
                t1.wait();
                System.out.println("perform some action");
                a1.resume();
            }

        }
    }
}

预期产量：

performing job.
perform some action
performing job.
perform some action
performing job.
perform some action
performing job.
perform some action
performing job.
perform some action

实际输出：

performing job.
performing job.
performing job.
performing job.
performing job.
perform some action

我不知道为什么即使我在job方法中发出了notify()信号,整个for循环仍在线程A中执行.

解决方法:

这是更简化的方式

public class TwoThread {

    public static void main(String[] args) throws InterruptedException {
        ThreadA a1 = new ThreadA();
        Thread t1 = new Thread(a1);

        synchronized (a1) {
            t1.start();
            for (int i = 0; i < 5; i++) {
                a1.wait();
                System.out.println("perform some action " + i);
                a1.notify();
            }

        }
    }
}

public class ThreadA implements Runnable {
    boolean suspended = false;
    boolean stopped = false;

    void job() throws InterruptedException {
        for (int i = 0; i < 5; i++)
            synchronized (this) {
                System.out.println("performing job. " + i);
                notify();
                wait();
            }
    }

    public void run() {
        try {
            job();
        } catch (InterruptedException e) {
            e.printStackTrace();
        }

    }

}

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