Open classes and methods in Kotlin - Mini Project: Build & Apply

Open Classes and Methods in Kotlin

📖 Scenario: You are creating a simple app that manages vehicles. You want to allow future changes by letting other developers add new types of vehicles or change how existing ones behave.

🎯 Goal: Learn how to make a class and its method open for extension in Kotlin. You will create an open class, then override its method in a subclass, and finally print the results.

📋 What You'll Learn

Create an open class named Vehicle with an open method drive() that returns a string.

Create a subclass named Car that inherits from Vehicle and overrides the drive() method.

Print the output of calling drive() on both Vehicle and Car objects.

💡 Why This Matters

🌍 Real World

Open classes and methods let developers design flexible software that can grow and change without rewriting existing code.

💼 Career

Understanding open classes is important for Kotlin developers working on apps that require customization and extension, such as Android apps or libraries.

1

Create an open class with an open method

Create an open class called Vehicle with an open method named drive() that returns the string "Driving a vehicle".

Kotlin

# Your code here

Need a hint?

Use the open keyword before the class and the method to allow them to be extended and overridden.

2

Create a subclass that overrides the method

Create a class called Car that inherits from Vehicle and overrides the drive() method to return the string "Driving a car".

Kotlin

open class Vehicle {
    open fun drive(): String {
        return "Driving a vehicle"
    }
}

# Your code here

Need a hint?

Use class Car : Vehicle() to inherit and override fun drive() to change the method.

3

Create objects and call the methods

Create a variable vehicle as an instance of Vehicle and a variable car as an instance of Car. Call the drive() method on both and store the results in variables vehicleDrive and carDrive.

Kotlin

open class Vehicle {
    open fun drive(): String {
        return "Driving a vehicle"
    }
}

class Car : Vehicle() {
    override fun drive(): String {
        return "Driving a car"
    }
}

# Your code here

Need a hint?

Create instances using val variableName = ClassName() and call methods with variable.method().

4

Print the results

Print the variables vehicleDrive and carDrive each on a new line.

Kotlin

open class Vehicle {
    open fun drive(): String {
        return "Driving a vehicle"
    }
}

class Car : Vehicle() {
    override fun drive(): String {
        return "Driving a car"
    }
}

val vehicle = Vehicle()
val car = Car()
val vehicleDrive = vehicle.drive()
val carDrive = car.drive()

# Your code here

Need a hint?

Use println() to show the text on the screen.