java多线程一个问题，就是为什么执行后，控制台为什么只打印了a为1然后就进入死循环，多线程刚学习的

public class Main implements Runnable {
    public Integer a = 1;
    public Integer b = 2;

    public static void main(String[] args) throws ExecutionException, InterruptedException {
        Main m = new Main();
        ExecutorService ser = Executors.newFixedThreadPool(3);
        ser.submit(m);
//        ser.submit(m);
        ser.shutdown();
    }

    @Override
    public void run() {
        while (true) {
            if (a <= 0) {
                break;
            }
            System.out.println(a);
            synchronized (a) {
                try {
                    a.wait();
                } catch (InterruptedException e) {
                    throw new RuntimeException(e);
                }
                a--;
            }
            b++;
            System.out.println(b);
            if (b >= 10) {
                synchronized (a) {
                    a.notify();
                }
            }
        }
    }
}

对象调用wait方法之后就会处于阻塞状态。将不会再向下执行，即输出1之后就不会执行了