Producer/Consumer - Calculate average time

Question

I have 4 class - Producer, Consumer, Shop, Main.

Trying to calculate average waiting time which customers are in the queue for waiting to enter the store.

My run method in Producer -

public void run() {
  for (int i = 1; i < size; i++) {

     shop.put(i);
     System.out.println("Customer number "  + i + " has entered the store\n");
     enterStore = System.currentTimeMillis();
     try {
        Thread.sleep((int) (Math.random() * 1000));

     } catch (InterruptedException e) { }
  }
}

Part of my put method in Shop -

System.out.println("The store is full! Customer " + value + " is waiting in the queue.....\n");
        queueStart = System.currentTimeMillis();
        System.out.println("Customer joined queue at time : " + queueStart);

        wait();

And part of my Main -

double averageTime = (Shop.queueStart - Producer.enterStore)/20;
  System.out.println("Average time customer queued outside store = " + averageTime);

Everything else in my code is working fine - but the average prints a minus number so I've obviously gone wrong somewhere. I'm really new to java and just looking for some help!

Thanks!

Answer 1

The later the time, the higher the double value, therefore you need to switch the subtraction operands, so that you get

Producer.enterStore - Shop.queueStart