java – 在notify上获取非法监视器状态异常

public class oddeven {
    static volatile Integer t = 0;

    public static void main(String as[]) {
        oddrunnable or = new oddrunnable(t);
        evenrunnable er = new evenrunnable(t);

        Thread t1 = new Thread(or,"odd");
        Thread t2 = new Thread(er,"even");

        t1.start();
        t2.start();

    }

}

class oddrunnable implements Runnable {
    Integer t;

    public oddrunnable(Integer t) {
        this.t = t;
    }

    @Override
    public void run() {
        // TODO Auto-generated method stub

        synchronized (t) {
            while (true) {

                if (t % 2 == 0) {
                    try {
                        t.wait();
                    } catch (InterruptedException e) {
                        // TODO Auto-generated catch block
                        e.printStackTrace();
                    }
                }
                System.out.println("Current thread id " + Thread.currentThread().getName());
                t++;
                t.notify();
            }
        }
    }

}

class evenrunnable implements Runnable {
    Integer t;

    public evenrunnable(Integer t) {
        this.t = t;
    }

    @Override
    public void run() {
        // TODO Auto-generated method stub

        // TODO Auto-generated method stub

        synchronized (t) {
            while (true) {

                if (t % 2 != 0) {
                    try {
                        t.wait();
                    } catch (InterruptedException e) {
                        // TODO Auto-generated catch block
                        e.printStackTrace();
                    }
                }
                System.out.println("Current thread id " + Thread.currentThread().getName());
                t++;
                t.notify(); // <-------------------exception on this line
            }
        }

    }

}

在同步对象本身上调用notify方法.不知道为什么会这样：

Current thread id even
Exception in thread "even" java.lang.IllegalMonitorStateException
    at java.lang.Object.notify(Native Method)
    at evenrunnable.run(oddeven.java:86)
    at java.lang.Thread.run(Thread.java:619)