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iOS Object-Oriented Swift 2.0 Class Inheritance Overriding Properties

Berry Loeffen
Berry Loeffen
4,303 Points
Posted by Berry Loeffen
Berry Loeffen
4,303 Points

What if there is no initial value for numberOfSeats?

Hi there,

Been trying to do some practice with initializing subclasses. What if the numberofseats constant did not have a value already when writing the property? How would i Have to write the code? property self.numberOfSeats not initialized at super.init call is the error i get. I have to initialize numberOfSeats, i get that, but whatever I try Xcode keeps coming up with an error

class Vehicle {
    var numberOfDoors: Int
    var numberOfWheels: Int

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

class Car: Vehicle {
    let numberOfSeats: Int

    override init(withDoors doors: Int, andWheels wheels: Int) {
        super.init(withDoors: doors, andWheels: wheels)
    }
}

2 Answers

jcorum
jcorum
71,830 Points

Close. You need the initializer to accept a formal parameter for the number of seats. Here I've called it seats. Because this init is now not overriding the super class's init, you can't say override. When you call this init you need to call it with 3 values. Then, with the seats value you initialize the sub class's member variable, and with the other two you initialize the inherited member variables by calling super.init(), as you were doing.

class Car: Vehicle {
    let numberOfSeats: Int

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

If you wanted to be able to create Cars without specifying a number of seats you could add a second init, one which does override the superclass's init:

    override init(withDoors doors: Int, andWheels wheels: Int) {
        numberOfSeats = 1
        super.init(withDoors: doors, andWheels: wheels)
    }

Then you would create your Cars in two different ways:

let c1 = Car(withDoors: 4, andWheels: 4)
let c2 = Car(withDoors: 2, andWheels: 4, seats: 2)
Berry Loeffen
Berry Loeffen
4,303 Points
Berry Loeffen
Berry Loeffen
4,303 Points

Correct me if i'm wrong, so we only override the init method if the superclass's and subclass's init are the same? Or offcourse if there is a new stored property that already has a value. If not we create a new init.

Thanks for the help!

jcorum
jcorum
71,830 Points
jcorum
jcorum
71,830 Points

One method overrides another if it has the same name, same method signature (number and type of parameters) and is in a different (sub) class. I think of the double r in override as "replacing or revising" the inherited method.

Since it's easy to confuse override and overload, I think of the l in overload as layering: layering on methods with the same name, different method signatures, all in the same class.