MessageQueue.java

package com.codecafe.concurrency.threadsignalling;

import java.util.ArrayList;
import java.util.List;

class MessageQueue {

  List<String> messages;
  int limit;

  // buffer is bounded
  public MessageQueue(int limit) {
    messages = new ArrayList<>();
    this.limit = limit;
  }

  public boolean isFull() {
    return messages.size() == limit;
  }

  public boolean isEmpty() {
    return messages.size() == 0;
  }

  public synchronized void enqueue(String message) throws InterruptedException {

    // releases the lock on the queue object and waits for the notification
    while (isFull()) {
      this.wait();
    }

    messages.add(message);

    // once producer sends the message, notify the consumer to consume the message
    this.notify();

    // and sleep
    Thread.sleep(100);
  }

  public synchronized String dequeue() throws InterruptedException {

    while (isEmpty()) {
      // wait till producer sends a message
      this.wait();
    }

    String message = messages.remove(0);

    // after consuming the message, signal the producer to send more messages
    this.notify();

    // and sleep
    Thread.sleep(1000);

    return message;
  }

}