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iOS Object-Oriented Swift 2.0 Class Inheritance Creating a Subclass

Instance for subclass?

Not sure about this ...

Challenge Task 1 of 1

In the editor, I have provided a class named Vehicle.

Your task is to create a subclass of Vehicle, named Car, that adds an additional stored property numberOfSeats of type Int with a default value of 4.

Once you've implemented the Car class, create an instance and assign it to a constant named someCar.

/Users/mattconway/Desktop/Screen Shot 2016-01-26 at 2.42.16 PM.png

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

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

// Enter your code below
class Car: Vehicle {
  var numberOfSeats: Int
  init(numberOfSeats: Int) {
    self.numberOfSeats = 4
  }
}

let someCars = Cars(numberOfSeats: 4)

Oops, I added an "s" to "someCar" and "Car" in the let statement. Still doesn't work in Playground and Challenge without the "s".

4 Answers

Hello:

You are doing great, the only thing is that you do not have to provide it with an init method, since it's already inheriting one from the super class. Just give the store property a default value of 4. And when creating the instance of it, then you will use the init from the base class.

class Vehicle {
    var numberOfDoors: Int
    var numberOfWheels: Int

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

// Enter your code below
class Car: Vehicle {
    var numberOfSeats: Int = 4

}

let someCar = Car(withDoors: 2, andWheels: 4)

Hope that helps.

I removed the init from Car class, but kept self.numberOfSeats and it still doesn't work. Made it worse, more errors now. Not sure???

Look at the answer again... Compare your code with the answer.

self.numberOfSeats should be removed. You only should add the store property and give it initial values or otherwise known as hardcoded values to it.

var numberOfSeats: Int = 4 

Good luck

Got the got that part. Trying to create an instance, "let someCar = Car()", it doesn't work. Neither does someCar.Car(). Actually I'm not really sure about the difference between the two.

You have to give values to the store properties through the init method.

Your Car class is inheriting from Vehicle class.. Vehicle class has an init method already implemented, therefore when you try to create an instance of "Car", you will be able to use the init it's inheriting from "Vehicle"

let someCar = Car(withDoors: 2, andWheels: 4)

See how (withDoors: Int, andWheels: Int) is implemented in the "Vehicle" class, but yet we are using it in the "Car" instance? That's because it's inheriting from it.

On my first answer, I gave you the whole code to the challenge, you can look at it, and compare it to yours and see what you are doing wrong.

Ok, got it all now. Thanks for clear explanations.

Daniel Aunspach
Daniel Aunspach
942 Points

Jhoan and Matt, thanks for posting the question and answer. I ran into trouble, as well along the same lines in that I also tried initializing the subclass (as it seemed to me the instructor advised in the lesson on overriding properties). Perhaps this code challenge should have been placed between the Inheritance and Overriding Properties videos?