Question

I am kind of new to object oriented programming and I am learning the concepts. Right now I only need help on just logically organizing the classes. The parts about the methods, attributes, and constructors I can figure out. I was assigned this following problem.

Holiday Travel Vehicles sells new recreational vehicles and travel
trailers. When new vehicles arrive at Holiday Travel Vehicles, a new
vehicle record is created. Included in the new vehicle record are a
vehicle serial number, name, model, year, manufacturer, and base cost.
When a customer arrives at Holiday Travel Vehicles, he or she works
with a salesperson to negotiate a vehicle purchase. When a purchase
has been agreed upon, a sales invoice is completed by the salesperson.
The invoice summarizes the purchase, including full customer
information, information on the trade-­‐in vehicle (if any), the
trade-­‐in allowance, and information on the purchased vehicle. If the
customer requests dealer-­‐installed options, they are listed on the
invoice as well. The invoice also summarizes the negotiated price,
plus any applicable taxes and license fees. The transaction concludes
with a customer signature on the sales invoice.

So far what I have thought of doing is making an invoice superclass with a customer and vehicle subclass since vehicle information and customer information is on the invoice. However since vehicles get records upon arrival to the dealership, I also thought about making vehicle it’s own class with the subclass travel trailer and RV since one involves an engine and one does not. However if I am doing vehicle records and vehicle information in an invoice I can’t make vehicle both it’s own class and a subclass of invoice.(If everything I am saying does not make sense, I am sorry I am just really confused.) So how should I arrange those classes? I am really lost.

Answer 1

Making vehicle and customer a sub-class of invoice doesn’t make a whole lot of sense. What I think you want is to make a vehicle class and a customer class, then within your invoice class you can hold an instance of the vehicle object and the customer object it dictates.

public class Invoice {
    private Vehicle MyVehicle;
    private Customer MyCustomer;
    //...etc
}

public class Customer {
    private String FirstName;
    //...etc
}

public class Vehicle{
    private String Model;
    //...etc
}

For travel trailer and RV class it makes more sense to sub-class vehicle since they are in essence a vehicle so will share many common variables with vehicles. The question you need to ask yourself is whether something is something else (an RV is a vehicle), or it points to something (an invoice has a reference to a vehicle). I hope that is clear, it is definitely something I remember struggling with as I first learned it.