public class WorkQueue {
    private final int nThreads;
    private final PoolWorker[] threads;
    private final LinkedList queue;


    public WorkQueue(int nThreads)
    {
        this.nThreads = nThreads;
        queue = new LinkedList();
        threads = new PoolWorker[nThreads];
  }


    public void start() {
        for (int i=0; i<nThreads; i++) {
            threads[i] = new PoolWorker();
            threads[i].start();
        }
    }

    public void execute(Runnable r) {
        synchronized(queue) {
            queue.addLast(r);
            queue.notify();
        }

    }

    private class PoolWorker extends Thread {
        public void run() {
            Runnable r;

            while (true) {

                synchronized(queue) {
                    System.out.println(queue.size());
                    while (queue.isEmpty()) {
                        try
                        {
                            queue.wait();
                        }
                        catch (InterruptedException ignored)
                        {

                        }
                    }

                    r = (Runnable) queue.removeFirst();
                }


                try {
                    r.run();
                }
                catch (RuntimeException e) {
                    throw new RuntimeException("Exception for method run()", e);
                }
            }
        }
    }
}

public class Main {


        public static void main(String[] args) throws InterruptedException {
            WorkQueue pool = new WorkQueue(2);
            pool.start();

            for (int i = 1; i < 10; i++) {
                final int finalI = i;
                pool.execute(new Factorial(finalI));
               
            }


            Thread.sleep(5_000);
            System.out.println("Done");

        }

}

public class Factorial implements Runnable {
    private final int fact;

    public Factorial(int fact) {
        this.fact = fact;
    }

    @Override
    public void run() {
        int result = 1;
        for (int j = 1; j < fact + 1; j++) {
            result += result * j;
            try {
                Thread.sleep(500);
            } catch (InterruptedException ignore) {
            }
        }
        System.out.println(Thread.currentThread()+" Result " + fact + " = " + result);
    }
}