@Override
    public final Customer findCustomer(String custNo){
        Customer custFound = null;
        for(int i = 0; i < customers.length; i++){
            if (custNo.equals(customers[i].getCustNo())){
                custFound = customers[i];
                break;
            }
        }
        if(custFound == null) {
            throw new IllegalArgumentException();
        }
        return custFound;
    }