异常捕获问题

class StopThread implements Runnable

{

	private boolean flag =true;

	public  void run()

	{

		while(flag)

		{

			

		try{

				wait();

			}

			catch(InterruptedException e)

			{

		System.out.println(Thread.currentThread().getName()+"....Exception");

		flag=false;

			}

			System.out.println(Thread.currentThread().getName()+"....run");

		}

	}

	public void changeFlag()

	{

		flag = false;

	}

}









class  StopThreadDemo

{

	public static void main(String[] args) 

	{

		StopThread st = new StopThread();

		

		Thread t1 = new Thread(st);

		Thread t2 = new Thread(st);

		t1.start();

		t2.start();



		int num = 0;



		while(true)

		{

			if(num++ == 60)

			{

				//st.changeFlag();

				t1.interrupt();

				//t2.interrupt();

				break;

			}

			System.out.println(Thread.currentThread().getName()+"......."+num);

		}

		System.out.println("over");

	}

}

运行时提示错误 ，
main....58
main....59
main....60
Exception in thread "Thread-1" java.lang.IllegalMonitorStateException
at java.lang.Object.wait(Native Method)
at java.lang.Object.wait(Object.java:503)
at my.operate.demo.StopThreadDemo.run(StopThread.java:33)
at java.lang.Thread.run(Unknown Source)
Exception in thread "Thread-0" java.lang.IllegalMonitorStateException
at java.lang.Object.wait(Native Method)
at java.lang.Object.wait(Object.java:503)
at my.operate.demo.StopThreadDemo.run(StopThread.java:33)
at java.lang.Thread.run(Unknown Source)
就是wait捕获异常不对？自己也没有写错啊，求高手啊
------解决方案--------------------

        synchronized (this) {

        	wait();

        }