21 interview questions on Kotlin for developers (2025)

Hard

9 votes754 runs0 comment

How to flatten a list of lists in Kotlin

Mobile developer

list

map

Anonymous authorat Jan 18, 2022

Medium

5 votes681 runs0 comment

Kotlin: Compile the following code and see the error.

Mobile developer

kotlin

null

Anonymous authorat Jan 18, 2022

Easy

5 votes680 runs1 comment

Write a function that returns the maximum of two integers in Kotlin

Mobile developer

functions

kotlin

Anonymous authorat Jan 18, 2022

Medium

3 votes591 runs

1 comment

Write a Kotlin program that evaluates an arithmetic expression.

Mobile developer

kotlin

data class

sealed class

Anonymous authorat Jan 18, 2022

Easy

2 votes566 runs0 comment

Print the value of a nullable string in Kotlin

Mobile developer

kotlin

null-safety

Anonymous authorat Jan 18, 2022

Easy

2 votes564 runs1 comment

Concatenate two strings in Kotlin

Mobile developer

string

concatenation

Vincent Cotroat Jan 18, 2022

Hard

2 votes560 runs1 comment

How to add a new element to a list of Kotlin data class

Mobile developer

kotlin

data class

inheritance

Anonymous authorat Jan 18, 2022

Expert

1 vote722 runs0 comment

In Kotlin, adding an element to a list does not change the list.

Mobile developer

list

immutable

Anonymous authorat Jan 18, 2022

Medium

1 vote619 runs

1 comment

In Kotlin, the infix function `add` can be used with two integers, but not with a float and an integer.

Mobile developer

infix

operators

Anonymous authorat Jan 18, 2022

Hard

1 vote606 runs0 comment

Use destructuring to extract the name and age of a User object

Mobile developer

data class

destructuring

Anonymous authorat Jan 18, 2022

Hard

1 vote576 runs0 comment

Write a function that takes a list of strings and returns a list of the same length, where each element is the length of the corresponding element in the input list.

Mobile developer

functions

lambdas

Anonymous authorat Jan 18, 2022

Medium

1 vote569 runs0 comment

Write a Kotlin code that prints 7 to the console.

Mobile developer

list

filter

drop

Anonymous authorat Jan 18, 2022

Hard

1 vote566 runs0 comment

Add a secondary constructor to a Kotlin class

Mobile developer

constructors

inheritance

Anonymous authorat Jan 18, 2022

Medium

1 vote563 runs0 comment

Create a data class with a vip property implementing the Human interface

Mobile developer

kotlin

data class

interfaces

Anonymous authorat Jan 18, 2022

Medium

0 vote596 runs

1 comment

Convert an Int to a Long in Kotlin

Mobile developer

kotlin

type conversion

Anonymous authorat Jan 18, 2022

Hard

0 vote533 runs0 comment

Write a Kotlin program that prints the following output: GA - Task from coroutine scope BU - Task from runBlocking ZO - Task from nested launch MEU - Coroutine scope is over

Mobile developer

coroutines

kotlin

Anonymous authorat Jan 18, 2022

Medium

0 vote421 runs0 comment

Write a valid call to the function reformat in Kotlin 1.3

Mobile developer

functions

parameters

Anonymous authorat Jan 18, 2022

Hard

0 vote235 runs0 comment

Which of the following "main" functions are invalid in Kotlin?

Mobile developer

functions

kotlin

Vincent Cotroat Jan 18, 2022

Medium

0 vote129 runs0 comment

In Kotlin, how to override a property in a subclass and call the superclass's property in the constructor?

Mobile developer

inheritance

overriding

ahmedat Mar 28, 2023

Easy

0 vote29 runs0 comment

What does the keyword "open" mean in Kotlin?

Mobile developer

inheritance

open

Mathieuat Nov 3, 2023

21 interview questions on Kotlinfor developers (2025)

Test your technical skills before an interview of Kotlin with 21 corrected questions. Beginner, Intermediate or Expert level.

How to flatten a list of lists in Kotlin

Kotlin: Compile the following code and see the error.

Write a function that returns the maximum of two integers in Kotlin

Write a Kotlin program that evaluates an arithmetic expression.

Print the value of a nullable string in Kotlin

Concatenate two strings in Kotlin

How to add a new element to a list of Kotlin data class

In Kotlin, adding an element to a list does not change the list.

In Kotlin, the infix function `add` can be used with two integers, but not with a float and an integer.

Use destructuring to extract the name and age of a User object

Write a function that takes a list of strings and returns a list of the same length, where each element is the length of the corresponding element in the input list.

Write a Kotlin code that prints 7 to the console.

Add a secondary constructor to a Kotlin class

Create a data class with a vip property implementing the Human interface

Convert an Int to a Long in Kotlin

Write a Kotlin program that prints the following output: GA - Task from coroutine scope BU - Task from runBlocking ZO - Task from nested launch MEU - Coroutine scope is over

Write a valid call to the function reformat in Kotlin 1.3

Which of the following "main" functions are invalid in Kotlin?

In Kotlin, how to override a property in a subclass and call the superclass's property in the constructor?

What does the keyword "open" mean in Kotlin?

21 interview questions on Kotlinfor developers (2025)

Test your technical skills before an interview of Kotlin with 21 corrected questions. Beginner, Intermediate or Expert level.

How to flatten a list of lists in Kotlin

Kotlin: Compile the following code and see the error.

Write a function that returns the maximum of two integers in Kotlin

Write a Kotlin program that evaluates an arithmetic expression.

Print the value of a nullable string in Kotlin

Concatenate two strings in Kotlin

How to add a new element to a list of Kotlin data class

In Kotlin, adding an element to a list does not change the list.

In Kotlin, the infix function `add` can be used with two integers, but not with a float and an integer.

Use destructuring to extract the name and age of a User object

Write a function that takes a list of strings and returns a list of the same length, where each element is the length of the corresponding element in the input list.

Write a Kotlin code that prints 7 to the console.

Add a secondary constructor to a Kotlin class

Create a data class with a vip property implementing the Human interface

Convert an Int to a Long in Kotlin

Write a Kotlin program that prints the following output: GA - Task from coroutine scope BU - Task from runBlocking ZO - Task from nested launch MEU - Coroutine scope is over

Write a valid call to the function reformat in Kotlin 1.3

Which of the following "main" functions are **invalid** in Kotlin?

In Kotlin, how to override a property in a subclass and call the superclass's property in the constructor?

What does the keyword "open" mean in Kotlin?

Which of the following "main" functions are invalid in Kotlin?