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iOS Object-Oriented Swift Class Inheritance Creating a Subclass

Posted by Alexander Mittendorfer
Alexander Mittendorfer
3,346 Points

These code challenges are getting way to complicated!! Please help, considering unsubscribing!!

Help pls.

objects.swift 
class Vehicle {
    var numberOfDoors: Int
    var numberOfWheels: Int

    init(withDoors doors: Int, andWheels wheels: Int) {
        self.numberOfDoors = doors
        self.numberOfWheels = wheels
    }
}

class Car: Vehicle {

    var numberOfSeats: Int

    override init(withDoors doors: Int, andWheels wheels: Int) {
        super.init(withDoors doors: Int, andWheels wheels: Int)
        self.numberOfSeats = 4
    }

}

let someCar = Car.init(withDoors: 5, andWheels: 5)

1 Answer

Steve Hunter
Steve Hunter
57,712 Points

Hi Alexander.

In this challenge we're using the super class/sub class relationship.

We have a super class called Vehicle. It has a few stored properties that can be set, which the init method takes care of. We want to be more specific and create a class of Car which is a type of Vehicle. It has one additional stored property that we're going to hard-code, i.e. set a default value.

To create a class we use the class keyword followed by the new class's name. If this new class is going to inherit the stuff in a super class, we use a colon, then the super class's name. For us, that would look like:

class Car: Vehicle

Next, the contents of the new class are contained within curly braces. Here, we just have a new stored property. That's called numberOfSeats. It is an Int and it is set to 4. Every sub class will call the super class's init method by default. We know that to create an instance of a class, every stored property must contain a value. Our new property has a value assigned to it in the sub class itself. The super class's init method requires the other stored properties passing in as parameters. Those are doors and wheels and they have the convenient labels added to make it read better, like withDoors:, andWheels.

So the new subclass just needs to inherit Vehicle; we've covered that. Then it needs to declare an Int called numberOfSeats and set it to 4. That looks like:

class Car: Vehicle {
  var numberOfSeats: Int = 4  
}

We then need to create a constant (use let) called someCar and create an instance of the new Car class. We know that this just needs the properties of Vehicle sending in. We've done the numberOfSeats inside the class itself and the init method from inside Vehicle will get called automatically. Try

let someCar = Car(withDoors: 4, andWheels: 4)

That does what's required.

Let me know how you get on. And don't unsubscribe; keep asking questions. There's lots of us around to help.

Keep me posted!

Steve.

Alexander Mittendorfer
Alexander Mittendorfer
3,346 Points

Thanks!

Steve Hunter
Steve Hunter
57,712 Points

Hey, no problem! :+1: :smile: