Inheritance in Kotlin: Exploring Properties and Methods

Welcome back! In this part of our Kotlin Class Basics Revision, we dive into inheritance, a fundamental concept in object-oriented programming (OOP) with Kotlin. Inheritance allows us to share code across classes, enhancing code organization and efficiency.

In this lesson, we'll explore attribute and method inheritance in Kotlin through practical examples. Our lesson's blueprint includes defining inheritance, examining attribute inheritance, exploring method inheritance, and understanding how to use the super keyword in Kotlin. Let’s dive in!

Inheritance involves creating a child class that inherits properties and functions from a parent class. In Kotlin, whenever classes share common properties or functions, inheritance becomes a relevant tool.

Here's an example featuring a parent class named Vehicle and a child class named Car:

// Define the parent class 'Vehicle'
open class Vehicle(val color: String, val brand: String)

// Define the child class 'Car', inheriting from 'Vehicle'
class Car(color: String, brand: String, val doors: Int) : Vehicle(color, brand)

Kotlin supports inheritance through classes, and single inheritance is our focus here, where one parent class serves one child class.

Attribute inheritance allows a child class to inherit the properties of a parent class.

Consider this example featuring a parent class named Artist, and a child class named Musician:

open class Artist(var name: String) // Parent class with an attribute

class Musician(name: String, var instrument: String) : Artist(name) // Child inherits parent's attribute

fun main() {
    val john = Musician("John Lennon", "Guitar")  // Creating a Musician instance
    println(john.name)   // Output: John Lennon
    println(john.instrument)   // Output: Guitar
}

The Musician class inherits the name property from the Artist class while having its own unique property, instrument.

Similar to properties, method inheritance allows a child class to inherit the functions of a parent class.

In the example below, the Car class can invoke the start function from the Vehicle class:

open class Vehicle(val brand: String) {
    open fun start() {
        println("The $brand is starting.")
    }
}

class Car(brand: String) : Vehicle(brand)

fun main() {
    val myCar = Car("BMW")
    myCar.start()   // Output: The BMW is starting.    
}