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iOS Object-Oriented Swift 2.0 Class Inheritance Creating a Subclass

William Hartvedt Skogstad
William Hartvedt Skogstad
5,857 Points
Posted by William Hartvedt Skogstad
William Hartvedt Skogstad
5,857 Points

I can´t get the initializer method right..

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.

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 = 4

    init(numberOfSeats: numberOfSeats) {

    }
}

let someCare = Car(numberOfDoors: 4, numberOfWheels: 4, numberOfSeats: 4)

2 Answers

Nathan Tallack
Nathan Tallack
22,160 Points
Nathan Tallack
Nathan Tallack
22,160 Points

Ok. There are two ways of going about this, and there are a few typo's you had that were probably making it difficult to work out.

The first (easy) way is this.

class Car: Vehicle {
    var numberOfSeats: Int = 4

}

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

We are not using an init method with your sublcass here because all of the properties you declare are either optional or have a default value (in your case the numberOfSeats has a default value). So what happens here when we declare your someCar we are using the initializer from the parent class (which is used if you dont define one in the subclass) to set the values up there in the parent class. Note that we are using the external parameter names when passing those values in. In this option we cannot declare your someCar with a different vlaue for numberOfSeats and can only initialize the object with that default value. We can change it later if we like.

The second (harder) way is this.

class Car: Vehicle {
    var numberOfSeats: Int = 4

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

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

Here we are declaring an initializer in our subclass. We are taking in a new parameter and in the initializer we are setting that with self.numberOfSeats. In this way we can (and must) pass in the numberOfSeats when we declare our someCar but in this case we are just passing in 4 so that it is the same as the default. Note also that we are calling the parent class initializer with the super.init function (which you do after you set all your own subclass properties) and we are passing into it the parameters that our initializer took when the object is being created. Again, we are taking care to use the external parameter names here as declared in the parent initializer (which are the same as what I am using in the subclass initializer) to make things easier.

I hope this helps. Watch those typo's, and keep up the great work! :)

Rich Braymiller
Rich Braymiller
7,119 Points
Rich Braymiller
Rich Braymiller
7,119 Points

Don't you LOVE how the teacher leaves out much of this stuff? SMH