异常解决 | IllegalMonitorStateException

package ConcurrentProgramme.OneProduceToOneClient;

public class P {
    private String lock;
    public P(String lock) {
        this.lock = lock;
    }

    public void setValue() {
        try {
            synchronized (lock) {
                if (!ValueObject.value.equals("")) {
                    lock.wait();
                }
                String value = System.currentTimeMillis() + "_" + System.nanoTime();
                System.out.println("设置的值是：" + value);
                ValueObject.value = value;
                lock.notify();
            }
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
    }
}

Exception in thread "Thread-0" java.lang.IllegalMonitorStateException
	at java.base/java.lang.Object.notify(Native Method)
	at ConcurrentProgramme.OneProduceToOneClient.P.setValue(P.java:18)
	at ConcurrentProgramme.OneProduceToOneClient.ThreadP.run(ThreadP.java:12)

在线线程中调用wait方法的时候 要用synchronized锁住对象，确保代码段不会被多个线程调用