Sleeping Barber, null.point.exception

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Java

Hello,

I have a problem with my Sleeping Barber problem code, and have looked at it for almost 12 hours now, and can't see whats wrong (maybe just a small mistake, that I could't see).

I will appreciate if anyone will look at it, and give me a hint about whats wrong :)

When i run the program, it says:

java.lang.NullPointerException
at BarberShop.barber(BarberShop.java:20) - the wait() method
at BarberShop.run(BarberShop.java:64) -
at BarberShop.main(BarberShop.java:55)

The code can be seen here on this link:

public class BarberShop
{
    private Barber barber;
    private Customer customer;
    private int waiting;
    private int chairs;
    private boolean isAvailable;
 
    public BarberShop()
    {
        waiting = 0;
        chairs = 5;
    }
 
    public void barber()
    {
        synchronized(this) {
            while(true) {
                try {
                    customer.wait();
                }
                catch (InterruptedException exception) {
                }
 
                waiting--;
                this.notify();
                barber.cutHair();
            }
        }
    }
 
    public void customer()
    {
        synchronized(this) {
            if(waiting < chairs) {
                waiting++;
                this.notify();
 
                try {
                    barber.wait();
                }
                catch (InterruptedException exception) {
                }
                customer.getHairCut();
            }
            else {
                //shop is full
            }
        }
    }
   
    public static void main(String args[])
    {
        BarberShop barberShop = new BarberShop();
        barberShop.run();
    }
 
    public void run()
    {
        final int barbers = 1;
 
        for(int i = 0 ; i < barbers ; i++) {
            barber = new Barber();
            barber();
        }
 
        int customerID = 1;
 
        while(true) {
            customer = new Customer(customerID++);
            customer();
 
            //             try {
            //                 //sleep();
            //             }
            //             catch (InterruptedException exception) {
            //             }
        }
 
    }
}

- Dennis