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iOS Object-Oriented Swift Class Inheritance Overriding Methods

Kanish Chhabra
Kanish Chhabra
2,151 Points
Posted by Kanish Chhabra
Kanish Chhabra
2,151 Points

How to initialize additional values of the subclass within subclass

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

    }
}

How do I initialize "numberOfSeats" within subclass "Car"

[MOD: edited code block - srh]

5 Answers

Steve Hunter
Steve Hunter
57,712 Points

Also, as the init method here is identical to the superclass, does it need to be there? The call to super init is implied, I think. So, does the new subclass just need to look like:

class Car : Vehicle {
  var numberOfSeats: Int = 4
  // omit the rest?
  // override init (withDoors doors: Int, andWheels wheels: Int) {
  //   super.init(withDoors: doors, andWheels: wheels)
  // }
}

Just thinking aloud but it's worth a try!

(I'll try it in the challenge ... )

[EDIT]

Yep - this worked in the challenge - I've not tried it in Xcode:

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

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

[EDIT2]

Yes, this also works in Xcode so the additional init method isn't required as it adds nothing to the super init method that is already defined. There's no override as the parameters being passed in are identical. Creating a subclass automatically calls the superclass init method. The new member variable, numberOfSeats is set within the Car class as a default value so doesn't need to be set by the subclass init method.

Make sense?

Steve.

Kanish Chhabra
Kanish Chhabra
2,151 Points
Kanish Chhabra
Kanish Chhabra
2,151 Points

Yeah I got it, but what if I wanted to initialize numberOfSeats using init method within the subclass?

Steve Hunter
Steve Hunter
57,712 Points

Hiya,

I'm out at the moment but I'll fire up Xcode when I get home and get an answer over to you ASAP.

I don't think you were too far off with your first suggestion.

Steve.

Steve Hunter
Steve Hunter
57,712 Points
Steve Hunter
Steve Hunter
57,712 Points

HI there,

You've done it already! But take the mention of numberOfSeats out of the init method. Just declare the numberOfSeats variable, call it an Int and assign the value 4 to it at the top of the class; just like you have done. And then, that's it!

class Car : Vehicle {
  var numberOfSeats: Int = 4
  override init (withDoors doors: Int, andWheels wheels: Int) {
    super.init(withDoors: doors, andWheels: wheels)
  }
}

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

I hope that helps.

Steve.

Steve Hunter
Steve Hunter
57,712 Points
Steve Hunter
Steve Hunter
57,712 Points

Hi Kanish,

This works:

class Car : Vehicle {
    var numberOfSeats: Int
    init(withDoors doors: Int, andWheels wheels: Int, andSeats seats: Int){
      self.numberOfSeats = seats
      super.init(withDoors: doors, andWheels: wheels)
    }
}

let someCar = Car(withDoors: 4, andWheels: 4, andSeats: 7)

Let me know if you want me to walk you through that code - I think you'll get it just fine.

Steve.

Kanish Chhabra
Kanish Chhabra
2,151 Points
Kanish Chhabra
Kanish Chhabra
2,151 Points

Sure. I did it your way, omitted the unnecessary 'override initializer' and I added the normal initializer for initialising value to 'numberOfSeats'. It worked but I wasn't able to initialize the value to 'numberOfDoors' and 'numberOfWheels'

Emin Grbo
Emin Grbo
13,092 Points
Emin Grbo
Emin Grbo
13,092 Points

You rock Steve !! :)) This totally makes sense. I was a bit confused why are we re-writing init method if it is already there. Now it is much clearer :))

Sometimes exercises get a bit confusing and make me thing something HAS TO BE DONE in that way. But i see it is better to experiment a bit and just make something that works ;)

Steve Hunter
Steve Hunter
57,712 Points

Hey, no problem! Glad to help. :+1: :smile: