Open classes and methods in Kotlin - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to make the class extendable.

Kotlin

open class Vehicle {
    fun drive() {
        println("Driving")
    }
}

class Car : [1] Vehicle() {}

Drag options to blanks, or click blank then click option'

Aabstract

Bopen

Cfinal

Dsealed

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'final' which prevents inheritance.

Forgetting to mark the class as 'open'.

In Kotlin, to allow a class to be inherited, it must be declared as open.

2fill in blank

medium

Complete the code to allow the method to be overridden.

Kotlin

open class Animal {
    [1] fun sound() {
        println("Some sound")
    }
}

Drag options to blanks, or click blank then click option'

Aopen

Bfinal

Coverride

Dabstract

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'final' which prevents overriding.

Using 'override' keyword in the base class.

Methods must be marked open to be overridden in subclasses.

3fill in blank

hard

Fix the error in the subclass method overriding.

Kotlin

open class Bird {
    open fun fly() {
        println("Flying")
    }
}

class Eagle : Bird() {
    override fun [1]() {
        println("Eagle flying")
    }
}

Drag options to blanks, or click blank then click option'

Aswim

Brun

Cfly

Djump

Attempts:

3 left

💡 Hint

Common Mistakes

Using a different method name in the override.

Forgetting to mark the base method as open.

The method name in the subclass must match the open method in the superclass to override it.

4fill in blank

hard

Fill both blanks to create an open class with an open method.

Kotlin

[1] class Shape {
    [2] fun draw() {
        println("Drawing shape")
    }
}

Drag options to blanks, or click blank then click option'

Aopen

Bfinal

Dabstract

Attempts:

3 left

💡 Hint

Common Mistakes

Marking class as open but method as final.

Forgetting to mark either class or method as open.

Both the class and the method must be marked open to allow inheritance and overriding.

5fill in blank

hard

Fill all three blanks to override an open method in a subclass.

Kotlin

open class Printer {
    open fun [1]() {
        println("Printing document")
    }
}

class ColorPrinter : Printer() {
    override fun [2]() {
        println([3])
    }
}

Drag options to blanks, or click blank then click option'

Aprint

C"Printing in color"

D"Printing in black and white"

Attempts:

3 left

💡 Hint

Common Mistakes

Using different method names in override.

Printing wrong message in subclass.

The method name must match in both classes, and the subclass method can provide a different implementation.