my own blocking queue for producer consumer

Question

I'm trying to implement my own blocking queue using wait-notify for producer-consumer pattern. The producer will produce a random string, and the consumer will consume the string and count it if the number of vowels is greater than 30%.

Queue:

public class Queue {
    private LinkedList<String> queue;
    private int size;
    private Object notEmpty = new Object();
    private Object notFull = new Object();

    public Queue(int size) {
        this.queue = new LinkedList<>();
        this.size = size;
    }

    public synchronized void insert(String str) throws InterruptedException {
        while (queue.size() == size) {
            notFull.wait();
        }
        queue.add(str);
        notEmpty.notifyAll();
    }

    public synchronized String remove() throws InterruptedException {
        while (queue.isEmpty()) {
            notEmpty.wait();
        }
        String str = queue.remove();
        notFull.notifyAll();
        return str;
    }
}

Producer:

public class Producer implements Runnable{

private Queue queue;

public Producer(Queue queue) {
    this.queue = queue;
}

@Override
public void run() {
    try {
        queue.insert(StringUtils.generateRandomString((100000)));
    } catch (InterruptedException e) {
        Thread.currentThread().interrupt();
    }
}

}

Consumer:

public class Consumer implements Runnable {

    private Queue queue;
    public static int count;

    public Consumer(Queue queue) {
        this.queue = queue;
    }

    @Override
    public void run() {
        try {
            String str = queue.remove();
            if ((double) StringUtils.countVowels(str) / str.length() >= 0.3) {
                count++;
            }
        } catch (InterruptedException e) {
            Thread.currentThread().interrupt();
        }
    }
}

Error:

java.lang.IllegalMonitorStateException
    at java.lang.Object.notifyAll(Native Method)
    at com.mambu.assignment3.Queue.insert
    at com.mambu.assignment3.Producer.run

Q: I don't understand why am I getting this error.