Super keyword in Kotlin

In this article we will learn about the use of super keywords.

Super keyword

Super keywords can be used to invoke the members of the parent class in the child class. In the example below, the child class invokes drive() and noOfSeats properties using the super keyword.

open class Vehicle(name: String, modelNumber: String, color: String) {
    val numberOfSeat = 3

    open fun drive() {
        println("Let's drive a vehicle")
    }
}

class Car(val name: String, val modelNumber: String, val color: String) : Vehicle(name, modelNumber, color) {

    override fun drive() {
        super.drive()
    }

    fun visitPlaces() {
        println("Let's visit places in our new car. We have ${super.numberOfSeat} seats")
    }
}

Super keyword can also be used to invoke the constructor of the parent class from the secondary constructors of the child class.

open class Vehicle(name: String, modelNumber: String, color: String) {
    val numberOfSeat = 3

    open fun drive() {
        println("Let's drive a vehicle")
    }
}

class Car : Vehicle {

    constructor(name: String, modelNumber: String, color: String) : super(name, modelNumber, color)

    override fun drive() {
        super.drive()
    }

    fun visitPlaces() {
        println("Let's visit places in our new car. We have ${super.numberOfSeat} seats")
    }
}

It can also be used to resolve the overriding conflicts. When we inherit from the two parent classes, which consist of methods with the same name, then we must specify which superclass’s implementation that we want to use using the super keyword.

open class Vehicle(name: String, modelNumber: String, color: String) {

    open val numberOfSeat = 4
    open fun drive() {
        println("Let's drive a vehicle")
    }
}

interface Instrument {
    fun drive()
}

class Car(val name: String, val modelNumber: String, val color: String) : Vehicle(name, modelNumber, color),
    Instrument {

    override fun drive() {
        super<Vehicle>.drive()
        println("Let's drive $name $modelNumber car of $color color")
    }

    fun visitPlaces() {
        println("Let's visit places in our new car. We have ${super.numberOfSeat} seats")
    }
}

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