Threads: Producer-Consumer Problem

Producer-Consumer problem is a very common question related to threads. Following is a simple solution to the problem. QueueClass represents the queue which both the Producer and Consumer has to access. The critical methods in the QueueClass - add() and remove() are synchronized in order to maintain the status quo between the Producer and Consumer threads.

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

public class ProducerConsumerTest {

 /**
  * @param args
  */
 public static void main(String[] args) {
  QueueClass q = new QueueClass();
  Producer p = new Producer(q, 10);
  Consumer c = new Consumer(q, 10);
  
  Thread t1 = new Thread(p);
  Thread t2 = new Thread(c);
  c.setpThread(t1);
  t1.start();
  t2.start();
 }

}

class Producer implements Runnable {
 QueueClass q;
 int size;
 
 Producer(QueueClass q, int size) {
  this.q = q;
  this.size = size;
 }

 public void run() {
  int index = -1;
  while(true) {
   q.add(new String("" + ++index));
   try {
    Thread.sleep(1000);
   }
   catch(InterruptedException e) {
    e.printStackTrace();
   }
  }
 }
}

class Consumer implements Runnable {
 QueueClass q;
 int size;
 Thread pThread;
 
 public void setpThread(Thread pThread) {
  this.pThread = pThread;
 }

 Consumer(QueueClass q, int size) {
  this.q = q;
  this.size = size;
 }

 public void run() {
  while(true) {
   q.remove();
   try {
    Thread.sleep(1000);
   }
   catch(InterruptedException e) {
    e.printStackTrace();
   }
  }
 }
}

class QueueClass {
 List queue = new ArrayList();
 int size = 10;
 
 public synchronized void add(String s) {
  if(getSize() < size) queue.add(s);
  System.out.println("Added: " + queue);
  try {
   if(getSize() >= size) {
    notifyAll();
    wait();
   }
  }
  catch(InterruptedException e) {
   e.printStackTrace();
  }
 }
 
 public synchronized void remove() {
  if(getSize() > 0) queue.remove(queue.size()-1);
  System.out.println("Removed: " + queue);
  try {
   if(getSize() <= 0) {
    notifyAll();
    wait();
   }
  }
  catch(InterruptedException e) {
   e.printStackTrace();
  }
 }
 
 public synchronized int getSize() {
  return queue.size();
 }
}