Why open keyword is required for inheritance in Kotlin - Test Your Understanding

Practice - 5 Tasks

1fill in blank

easy

Complete the code to declare a class that can be inherited.

Kotlin

open class Animal {
    fun sound() {
        println("Animal sound")
    }
}

class Dog : [1]() {
}

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

Afun

Bopen

Cclass

DAnimal

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'open' instead of the class name after the colon.

Forgetting to specify the parent class name.

The class Dog inherits from Animal. The open keyword on Animal allows inheritance.

2fill in blank

medium

Complete the code to allow the function to be overridden in a subclass.

Kotlin

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

class Car : Vehicle() {
    override fun [1]() {
        println("Driving car")
    }
}

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

AVehicle

Bopen

Cdrive

Doverride

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'open' or 'override' as the function name.

Changing the function name in the subclass.

The function drive is overridden in the subclass Car. The open keyword on the base function allows this.

3fill in blank

hard

Fix the error by adding the required keyword to allow inheritance.

Kotlin

class Person {
    fun greet() {
        println("Hello")
    }
}

class Student : [1]() {
}

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

APerson

Bopen Person

Copen

DPerson open

Attempts:

3 left

💡 Hint

Common Mistakes

Trying to inherit from a class not marked as open.

Adding 'open' in the wrong place.

The class Person must be marked open to allow inheritance. Since it is not, inheritance causes an error.

4fill in blank

hard

Fill both blanks to create an open class and override its function.

Kotlin

class [1] {
    fun greet() {
        println("Hi")
    }
}

class Friend : [2]() {
    override fun greet() {
        println("Hello friend")
    }
}

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

Aopen Friend

BFriend

Copen Person

DPerson

Attempts:

3 left

💡 Hint

Common Mistakes

Not marking the base class as open.

Trying to override a function without the base function being open.

The base class Person must be declared open to allow inheritance and function overriding. The subclass Friend inherits from Person.

5fill in blank

hard

Fill all three blanks to define an open class, an open function, and override it in a subclass.

Kotlin

class [1] {
    [2] fun speak() {
        println("Speaking")
    }
}

class Teacher : [3]() {
    override fun speak() {
        println("Teaching")
    }
}

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

Aopen Person

Bopen

CPerson

DTeacher

Attempts:

3 left

💡 Hint

Common Mistakes

Not marking the function as open.

Not marking the base class as open.

The base class Person is declared normally. The function speak is marked open to allow overriding. The subclass Teacher inherits from Person which must be marked open to allow inheritance.