Thread Communication Using Wait and Notify in Java

package com.concretepage;
import java.util.ArrayList;
import java.util.List;
public class WaitNotifyTest {
    private static Object lock = new Object();
    private static List<String> list = new ArrayList<String>();
    public static void main(String[] args) {
        new Producer().start();
        new Consumer().start();
    }
    static class Producer extends Thread {
        @Override
        public void run() {
            while (true){
            	synchronized (lock) {
            		if(list.size()==0){
            			System.out.println("Producer added A");
            			list.add("A");
            			try {
				    lock.wait();
				} catch (InterruptedException e) {
							e.printStackTrace();
				}
            		}
            		lock.notify();
            	}	
            }
        }
    }
    static class Consumer extends Thread{
        @Override
        public void run() {
           while (true){
        	   synchronized (lock) {
        		   if(list.size()==1){
        			   System.out.println("Consumer consumes A");
        			   list.remove(0);
        			   lock.notify();
        			   try {
					 lock.wait();
				   } catch (InterruptedException e) {
						e.printStackTrace();
				   }
        		   }
	                   try {
	                     Thread.sleep(1000);
	                   } catch (InterruptedException e) { e.printStackTrace(); }
	               
        	   }
           }   
        }
   }
} 

Producer added A
Consumer consumes A
Producer added A
Consumer consumes A
Producer added A
Consumer consumes A
Producer added A
Consumer consumes A
Producer added A
----------------
----------------