what's wrong with my java(producer-consumer) code?

Question

I wrote this java code with synchronized and busy waiting but I don't know why it doesn't work right! for example I get this output

produced:6
produced:7
consumed:0
consumed:0

how 6 and 7 are produced but 0 is consumed ??? I don't know what's wrong with it,please help me ,here is my code:

package conper;
import java.util.*;
import java.util.concurrent.TimeUnit;

class Queue<Integer> {

    int items=0;
    int q=0;
    public int[] array= new int[10];

    Queue(int i) {

    }
    public boolean isEmpty(){
        if (this.q > 0)
        {
            return false ;
        }else{

            return true ;}
    }
    public boolean isFull(){
        if (this.q > 10)
        {

            return true ;
        }else{

            return false ;
        }
    }
    public int size(){
        return items;
    }


   public synchronized void add(int x){
         if(!isFull()){
            array[++q]=x;


         }
    }
    public synchronized void remove(int x){
        if(!isEmpty()){
            array[--q]=x;

        }
    }
}
class Producer implements Runnable {

    private Random random = new Random();

    private Queue<Integer> queue;
    private boolean working = true;


    public Producer(Queue<Integer> q) {
        queue = q;

    }

    public void run() {
        int product=0;
        int loop = random.nextInt(10) + 20;
        for (int i = 0; i < loop; i++) {
            double h = Math.pow(2, Math.E * i);

        }

        while(working){
            product = produce();
            if(!queue.isFull() ){
                break;

            }

        }
        queue.add(product);
        System.out.println("produced:"+product);

    }
     public void stop() {
        working = false;
    }
       private int produce() {
        int result = 0;
        int loop = random.nextInt(10) + 20;
        for (int i = 0; i < loop; i++) {
            double h = Math.pow(2, Math.E * i);

        }
        result = random.nextInt(10);
        return result;
    }

    }
class Consumer implements Runnable {

    private Random rnd = new Random();

    private Queue<Integer> queue;
    private boolean working = true;


    public Consumer(Queue<Integer> q) {
        queue = q;

    }

    public void run() {

        int product = 0;
        while(working){

            if(!queue.isEmpty())
                break;

        }
        queue.remove(product);

        System.out.println("consumed:"+product);


        consume(product);
    }
     public void stop() {
        working = false;
    }
     public void consume(int product) {
        int loop = rnd.nextInt(10000) + 2000;
        for (int i = 0; i < loop; i++) {
            double h = Math.pow(2, Math.E * i);
        }

    }
}
public class Main {
    public static void main(String[] args) {

        Queue<Integer> queue = new Queue<Integer>(5);

        Producer p1 = new Producer(queue);
        Producer p2 = new Producer(queue);

        Consumer c1 = new Consumer(queue);
        Consumer c2 = new Consumer(queue);



        Thread pt1 = new Thread(p1);
        Thread pt2 = new Thread(p2);

        Thread ct1 = new Thread(c1);
        Thread ct2 = new Thread(c2);


        pt1.start();
        pt2.start();

        ct1.start();
        ct2.start();

        try {
            TimeUnit.MILLISECONDS.sleep(200);

            p1.stop();
            p2.stop();

            c1.stop();
            c2.stop();
        }

        catch (Exception e) {
            return;
        }

    }


    }

any suggestion?

Answer 1

Your consumer code reads

int product = 0;
// code which doesn't change "product"
System.out.println("consumed:"+product);

I suggest you need a remove() method which returns the value from the queue instead of being passed a value.

I also suggest you get the code to work in one thread before attempting to use in multiple threads.