Interface declaration and implementation in Kotlin - Mini Project: Build & Apply

Interface declaration and implementation

📖 Scenario: You are creating a simple program to represent different types of vehicles. Each vehicle can start and stop. You will use an interface to define these actions and then create classes that implement this interface.

🎯 Goal: Build a Kotlin program that declares an interface called Vehicle with two functions: start() and stop(). Then create two classes, Car and Bike, that implement the Vehicle interface. Finally, create objects of these classes and call their start() and stop() functions.

📋 What You'll Learn

Declare an interface called Vehicle with two functions: start() and stop()

Create a class called Car that implements the Vehicle interface

Create a class called Bike that implements the Vehicle interface

In both classes, provide simple print statements inside start() and stop() functions

Create objects of Car and Bike and call their start() and stop() functions

💡 Why This Matters

🌍 Real World

Interfaces are used in real-world apps to define common behaviors for different objects, like vehicles, users, or devices, so they can be handled in a uniform way.

💼 Career

Understanding interfaces is important for Kotlin developers to write clean, modular, and maintainable code, especially in Android app development and backend services.

1

Declare the Vehicle interface

Declare an interface called Vehicle with two functions: start() and stop(). Both functions should have no parameters and no return value.

Kotlin

// Declare interface Vehicle with start() and stop() functions
// Your code here

Need a hint?

Use the interface keyword to declare an interface. Inside, declare two functions start() and stop() without bodies.

2

Create the Car class implementing Vehicle

Create a class called Car that implements the Vehicle interface. Override the start() function to print "Car started" and the stop() function to print "Car stopped".

Kotlin

interface Vehicle {
    fun start()
    fun stop()
}

// Create class Car implementing Vehicle
// Your code here

Need a hint?

Use class Car : Vehicle to implement the interface. Use override keyword for the functions and add println statements inside.

3

Create the Bike class implementing Vehicle

Create a class called Bike that implements the Vehicle interface. Override the start() function to print "Bike started" and the stop() function to print "Bike stopped".

Kotlin

interface Vehicle {
    fun start()
    fun stop()
}

class Car : Vehicle {
    override fun start() {
        println("Car started")
    }

    override fun stop() {
        println("Car stopped")
    }
}

// Create class Bike implementing Vehicle
// Your code here

Need a hint?

Similar to Car, create Bike class implementing Vehicle and override the functions with print statements.

4

Create objects and call functions

Create an object called myCar of type Car and an object called myBike of type Bike. Call start() and stop() on both objects.

Kotlin

interface Vehicle {
    fun start()
    fun stop()
}

class Car : Vehicle {
    override fun start() {
        println("Car started")
    }

    override fun stop() {
        println("Car stopped")
    }
}

class Bike : Vehicle {
    override fun start() {
        println("Bike started")
    }

    override fun stop() {
        println("Bike stopped")
    }
}

// Create objects myCar and myBike
// Call start() and stop() on both
// Your code here

Need a hint?

Create objects using val myCar = Car() and val myBike = Bike(). Then call start() and stop() on each object. Put this code inside a main() function.