Producer consumer problem using wait and notify

We have a shared Queue and two threads called Producer and Consumer. Producer thread puts number into shared queue and Consumer thread consumes numbers from shared bucket. Condition is that once an item is produced, consumer thread has to be notified and similarly after consumption producer thread needs to be notified. This inter thread communication is achieved using wait and notify method. Remember wait and notify method is defined in object class, and they are must be called inside synchronized block.

package concurrency;

import java.util.LinkedList;

import java.util.Queue;

import org.apache.log4j.Logger;

public class InterThreadCommunicationExample {

    public static void main(String args[]) {

        final Queue sharedQ = new LinkedList();

        Thread producer = new Producer(sharedQ);

        Thread consumer = new Consumer(sharedQ);

        producer.start();

        consumer.start();

    }

}

public class Producer extends Thread {

    private static final Logger logger = Logger.getLogger(Producer.class);

    private final Queue sharedQ;

    public Producer(Queue sharedQ) {

        super("Producer");

        this.sharedQ = sharedQ;

    }

    @Override

    public void run() {

        for (int i = 0; i < 4; i++) {

            synchronized (sharedQ) {

                //waiting condition - wait until Queue is not empty

                while (sharedQ.size() >= 1) {

                    try {

                        logger.debug("Queue is full, waiting");

                        sharedQ.wait();

                    } catch (InterruptedException ex) {

                        ex.printStackTrace();

                    }

                }

                logger.debug("producing : " + i);

                sharedQ.add(i);

                sharedQ.notify();

            }

        }

    }

}

public class Consumer extends Thread {

    private static final Logger logger = Logger.getLogger(Consumer.class);

    private final Queue sharedQ;

    public Consumer(Queue sharedQ) {

        super("Consumer");

        this.sharedQ = sharedQ;

    }

    @Override

    public void run() {

        while(true) {

            synchronized (sharedQ) {

                //waiting condition - wait until Queue is not empty

                while (sharedQ.size() == 0) {

                    try {

                        logger.debug("Queue is empty, waiting");

                        sharedQ.wait();

                    } catch (InterruptedException ex) {

                        ex.printStackTrace();

                    }

                }

                int number = sharedQ.poll();

                logger.debug("consuming : " + number );

                sharedQ.notify();

              

                //termination condition

                if(number == 3){break; }

            }

        }

    }

}