How deep do you take the Has-a when it comes to Object Oriented Design?

Question

If I say a car has a certain number of tires, a tire size, a tire brand, then I am guessing I could make a class like this:

public class Car
{
    public int TireCount {get;set;}
    public float TireSize {get;set;}
    public string TireBrand {get;set;}
}

On the other hand, I could make Tire a class and then make that a property of the class Car like so:

public class Tire
{
   public int Count {get;set;}
   public float Size {get;set;}
   public string Brand {get;set;}
}

public class Car
{
    public Tire tire {get;set;}
}

What is the better way? How deep do I take the relationship? Is it possible to over Object if that there is such as saying?

Answer 1

Personally, I would have "Size" and "Brand" be members of Tire, since they're specific to a specific type of Tire.

Car, on the other hand, should probably have a collection of Tires, since you could (theoretically) have multiple tires, of differing types.

I would do it more like:

public class Tire
{
    public float Size {get;set;}
    public string Brand {get;set;}
}

public class Car
{
    public IList<Tire> Tires {get; private set;}
}

Answer 2

As deep as it makes sense to go for your application.

In your example, your Car class would have multiple properties related to tires...so a Tire class (or collection of Tires) makes sense. Probably something like:

public class Tire
{
    public float Size {get; set;}
    public string Brand {get; set;}
}

public class Car
{
    public List<Tire> Tires {get; private set;}
}

Then you could do:

Car myCar = new Car();

// Some initialization here

int tireCount = myCar.Tires.Count();

To get the count of tires.

Answer 3

I would go until I'm sure I wont have to duplicate the information

in that case I might need an instance of the tire only