public class Customer extends Thread {
    BarberShop barberShop;

    Customer(BarberShop barberShop) {
        this.barberShop = barberShop;
    }

    @Override
    public void run() {
        try {
            Thread.sleep(Math.round((Math.random() * 1000)));
            barberShop.enterShop();
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
    }

    // this is called by the barber thread to continue execution after
    // this object was waiting in the queue
    void sitInBarbersChair() throws InterruptedException {
        barberShop.getHaircut(this);
    }
}