100 Must-Know Kotlin Interview Questions and Answers 2025

Kotlin Fundamentals

1.
What is Kotlin and how does it interoperate with Java?
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2.
How does Kotlin improve upon Java for Android development?
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3.
What are the basic types in Kotlin?
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4.
Explain the difference between val and var in Kotlin.
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5.
How do you create a singleton in Kotlin?
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6.
What are the Kotlin type inference rules?
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7.
Can Kotlin code be executed without a main function?
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8.
What is the purpose of the Unit type in Kotlin?
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9.
How do you perform string interpolation in Kotlin?
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10.
What are extension functions in Kotlin?
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Kotlin Control Flow and Error Handling

11.
How are if expressions used in Kotlin as compared to Java?
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12.
Explain when expressions in Kotlin.
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13.
How does Kotlin handle null safety and what is the Elvis operator?
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14.
What is a “smart cast” in Kotlin?
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15.
How do you implement a custom getter and setter in Kotlin?
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16.
Describe exception handling in Kotlin.
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17.
What are the differences between throw, try, catch, and finally in Kotlin versus other languages?
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18.
How does Kotlin’s Nothing type work in control flow?
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Kotlin Classes and Objects

19.
How do you create classes in Kotlin?
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20.
Explain primary and secondary constructors in Kotlin.
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21.
What are data classes in Kotlin?
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22.
How does inheritance work in Kotlin?
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23.
What are sealed classes in Kotlin?
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24.
Explain how properties and fields differ in Kotlin.
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25.
What is object expression and when do you use it?
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26.
What are companion objects in Kotlin?
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27.
How do you define an enum in Kotlin?
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Kotlin Functions and Lambdas

28.
How do you define functions in Kotlin?
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29.
What is a higher-order function in Kotlin?
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30.
What is the purpose of inline functions?
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31.
How do you use lambdas in Kotlin?
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32.
Explain the use of with and apply in Kotlin.
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33.
What are tail recursive functions and how do you define one in Kotlin?
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34.
What are default and named parameters in Kotlin?
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Kotlin Collections and Functional Constructs

35.
How do you use lists, sets, and maps in Kotlin?
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36.
What is the difference between map and flatMap in Kotlin?
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37.
Explain lazy collection evaluation in Kotlin.
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38.
What are the different ways to iterate over a collection in Kotlin?
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39.
What are sequence in Kotlin and when should you use them?
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40.
How do you transform a collection by applying a function to each element in Kotlin?
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Kotlin Coroutines and Concurrency

41.
What are coroutines in Kotlin and how do they compare to threads?
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42.
How do you launch a coroutine?
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43.
Explain the structure of a coroutine with a launch and async example.
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44.
What is a suspend function in Kotlin?
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45.
Explain the context of coroutines and how do you manage it.
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46.
What are coroutine scopes and why are they important?
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47.
How do you cancel a coroutine and handle exceptions in coroutines?
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48.
Can coroutines be used on any thread or are there restrictions?
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Kotlin Interoperability

49.
How is Kotlin-Java interoperability achieved?
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50.
Can you call Kotlin code from Java?
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51.
Can Java annotations be used in Kotlin? How?
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52.
What is the @JvmStatic, @JvmOverloads, @JvmField, and @JvmName annotation and when do you use them?
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53.
How do you use Java Streams in Kotlin?
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Kotlin Advanced Topics

54.
What is the role of delegation in Kotlin?
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55.
How do you manage dependency injection in Kotlin?
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56.
What is type aliasing in Kotlin and why would you use it?
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57.
How are generics handled in Kotlin compared to Java?
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58.
What is the difference between a vararg and an array in Kotlin?
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59.
Explain destructuring declarations in Kotlin.
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60.
How do you create and use an inline class in Kotlin?
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Kotlin Android Specific

61.
How do you ensure non-null view properties in Android with Kotlin?
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62.
What are the benefits of using Kotlin in Android development?
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63.
Explain how to use Kotlin Android Extensions.
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64.
How do you handle configuration changes in Android using Kotlin?
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65.
What is an Android LiveData and how do you use it in Kotlin?
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66.
How does Kotlin improve working with Android’s concurrency APIs like AsyncTask?
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67.
What is the purpose of coroutineScope or lifecycleScope in Android with Kotlin?
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Kotlin DSL and Meta-Programming

68.
What is a domain-specific language (DSL) in Kotlin, and how would you create one?
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69.
How do Kotlin extension functions facilitate DSL creation?
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70.
What are the common use-cases for Kotlin’s reflective capabilities?
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71.
How does Kotlin’s apply, let, run, with, and also improve DSL writing?
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Kotlin Multiplatform and Cross-Platform Development

72.
What is Kotlin Multiplatform Mobile (KMM)?
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73.
Explain how Kotlin/Native works and what it offers for cross-platform development.
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74.
How can shared business logic be developed with Kotlin Multiplatform?
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75.
What are the limitations of Kotlin Multiplatform?
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76.
Discuss the build system and tooling support for Kotlin Multiplatform projects.
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Kotlin Testing and Tooling

77.
What testing frameworks are available for Kotlin?
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78.
How do you mock dependencies in Kotlin unit tests?
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79.
What are some of the best practices for writing testable Kotlin code?
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80.
How does the Kotlin REPL work and what can it be used for?
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Kotlin Asynchronous Flow

81.
What is a Flow in Kotlin and how does it differ from a coroutine?
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82.
How would you handle backpressure in Kotlin?
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83.
Show an example of a cold flow versus hot channels in Kotlin.
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84.
How do you convert a callback-based API to Kotlin suspend function?
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Kotlin Project and Environment Setup

85.
How do you set up a Kotlin project using Gradle?
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86.
What is the Kotlin script (.kts) file and how is it used?
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87.
How do you manage Kotlin project dependencies effectively?
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88.
What is Kotlin style guide and why should you follow it?
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Kotlin Best Practices

89.
What are the recommended conventions for naming and organizing Kotlin files?
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90.
How do you avoid common pitfalls with Kotlin’s nullability?
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91.
What are some best practices to optimize Kotlin code for performance?
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92.
How do you effectively use scope functions?
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Kotlin Future Directions

93.
Discuss how coroutines have evolved in Kotlin and what the future might hold.
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94.
What upcoming features are projected for Kotlin that developers should be aware of?
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95.
How is Kotlin being adopted for backend development, and why would you choose it over traditional Java frameworks?
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96.
What impact does Google’s official support for Kotlin have on its adoption?
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Kotlin Miscellaneous

97.
How do you serialize and deserialize JSON in Kotlin?
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98.
Discuss how Kotlin manages memory and garbage collection.
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99.
What are the benefits of using Kotlin for server-side development?
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100.
Explain some common Kotlin idioms for handling common programming tasks.
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100 Kotlin interview questions

What is Kotlin and how does it interoperate with Java?

How does Kotlin improve upon Java for Android development?

What are the basic types in Kotlin?

Explain the difference between val and var in Kotlin.

How do you create a singleton in Kotlin?

What are the Kotlin type inference rules?

Can Kotlin code be executed without a main function?

What is the purpose of the Unit type in Kotlin?

How do you perform string interpolation in Kotlin?

What are extension functions in Kotlin?

How are if expressions used in Kotlin as compared to Java?

Explain when expressions in Kotlin.

How does Kotlin handle null safety and what is the Elvis operator?

What is a “smart cast” in Kotlin?

How do you implement a custom getter and setter in Kotlin?

Describe exception handling in Kotlin.

What are the differences between throw, try, catch, and finally in Kotlin versus other languages?

How does Kotlin’s Nothing type work in control flow?

How do you create classes in Kotlin?

Explain primary and secondary constructors in Kotlin.

What are data classes in Kotlin?

How does inheritance work in Kotlin?

What are sealed classes in Kotlin?

Explain how properties and fields differ in Kotlin.

What is object expression and when do you use it?

What are companion objects in Kotlin?

How do you define an enum in Kotlin?

How do you define functions in Kotlin?

What is a higher-order function in Kotlin?

What is the purpose of inline functions?

How do you use lambdas in Kotlin?

Explain the use of with and apply in Kotlin.

What are tail recursive functions and how do you define one in Kotlin?

What are default and named parameters in Kotlin?

How do you use lists, sets, and maps in Kotlin?

What is the difference between map and flatMap in Kotlin?

Explain lazy collection evaluation in Kotlin.

What are the different ways to iterate over a collection in Kotlin?

What are sequence in Kotlin and when should you use them?

How do you transform a collection by applying a function to each element in Kotlin?

What are coroutines in Kotlin and how do they compare to threads?

How do you launch a coroutine?

Explain the structure of a coroutine with a launch and async example.

What is a suspend function in Kotlin?

Explain the context of coroutines and how do you manage it.

What are coroutine scopes and why are they important?

How do you cancel a coroutine and handle exceptions in coroutines?

Can coroutines be used on any thread or are there restrictions?

How is Kotlin-Java interoperability achieved?

Can you call Kotlin code from Java?

Can Java annotations be used in Kotlin? How?

What is the @JvmStatic, @JvmOverloads, @JvmField, and @JvmName annotation and when do you use them?

How do you use Java Streams in Kotlin?

What is the role of delegation in Kotlin?

How do you manage dependency injection in Kotlin?

What is type aliasing in Kotlin and why would you use it?

How are generics handled in Kotlin compared to Java?

What is the difference between a vararg and an array in Kotlin?

Explain destructuring declarations in Kotlin.

How do you create and use an inline class in Kotlin?

How do you ensure non-null view properties in Android with Kotlin?

What are the benefits of using Kotlin in Android development?

Explain how to use Kotlin Android Extensions.

How do you handle configuration changes in Android using Kotlin?

What is an Android LiveData and how do you use it in Kotlin?

How does Kotlin improve working with Android’s concurrency APIs like AsyncTask?

What is the purpose of coroutineScope or lifecycleScope in Android with Kotlin?

What is a domain-specific language (DSL) in Kotlin, and how would you create one?

How do Kotlin extension functions facilitate DSL creation?

What are the common use-cases for Kotlin’s reflective capabilities?

How does Kotlin’s apply, let, run, with, and also improve DSL writing?

What is Kotlin Multiplatform Mobile (KMM)?

Explain how Kotlin/Native works and what it offers for cross-platform development.

How can shared business logic be developed with Kotlin Multiplatform?

What are the limitations of Kotlin Multiplatform?

Discuss the build system and tooling support for Kotlin Multiplatform projects.

What testing frameworks are available for Kotlin?

Explain the difference between `val` and `var` in Kotlin.

Can Kotlin code be executed without a `main` function?

What is the purpose of the `Unit` type in Kotlin?

How are `if` expressions used in Kotlin as compared to Java?

Explain `when` expressions in Kotlin.

What are the differences between `throw`, `try`, `catch`, and `finally` in Kotlin versus other languages?

How does Kotlin’s `Nothing` type work in control flow?

Explain the use of `with` and `apply` in Kotlin.

What is the difference between `map` and `flatMap` in Kotlin?

Explain `lazy` collection evaluation in Kotlin.

What are `sequence` in Kotlin and when should you use them?

Explain the structure of a coroutine with a `launch` and `async` example.

What is the `@JvmStatic`, `@JvmOverloads`, `@JvmField`, and `@JvmName` annotation and when do you use them?

What is the difference between a `vararg` and an array in Kotlin?

What is the purpose of `coroutineScope` or `lifecycleScope` in Android with Kotlin?

How does Kotlin’s `apply`, `let`, `run`, `with`, and `also` improve DSL writing?

What is the Kotlin script (`.kts`) file and how is it used?