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All Kotlin Interview Questions

Practice the complete collection of Kotlin interview questions including theory, coding, MCQs and real interview problems.

Total Questions: 81Topics: 39Complete interview preparation

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All Kotlin Interview Questions (81)

Scroll through every important Kotlin question asked in real interviews. Includes MCQs, subjective questions, and coding prompts.

1. What is Kotlin?

Difficulty: EasyType: MCQTopic: Kotlin Basics

A modern, statically-typed programming language that runs on JVM
A JavaScript framework
A database management system
An operating system

Kotlin is a modern, statically-typed programming language developed by JetBrains that runs on the Java Virtual Machine and can also be compiled to JavaScript or native code. It is fully interoperable with Java, meaning you can use Java libraries and frameworks in Kotlin and vice versa. Kotlin was officially announced as a preferred language for Android development by Google in 2019, and it offers features like null safety, extension functions, coroutines, and concise syntax that make development more productive and safer.

Correct Answer: A modern, statically-typed programming language that runs on JVM

2. What is the difference between val and var in Kotlin?

Difficulty: EasyType: MCQTopic: Variables

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All Kotlin Interview Questions

Overview

1. What is Kotlin?

2. What is the difference between val and var in Kotlin?

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3. What does the ? operator mean in Kotlin type declarations?

4. How do you insert a variable into a string in Kotlin?

5. What is type inference in Kotlin?

6. What does the ?: (Elvis operator) do in Kotlin?

7. What happens when you use the ?. (safe call) operator on a null object?

8. What does the !! (not-null assertion) operator do and when should you use it?

9. What are the main advantages of Kotlin over Java?

10. Explain the difference between val and var with examples and when to use each.

11. Explain Kotlin's null safety system and the different operators for handling nulls.

12. How do you work with strings in Kotlin including templates, multi-line strings, and common operations?

13. Explain type casting in Kotlin including smart casts, safe casts, and unsafe casts.

14. What are the basic data types in Kotlin and how do they differ from Java primitives?

15. Explain operator overloading in Kotlin and how it differs from Java.

16. How does Kotlin achieve interoperability with Java and what challenges might you face?

17. What is the correct syntax to declare a function in Kotlin?

18. How do you define default parameter values in Kotlin functions?

19. What are extension functions in Kotlin?

20. What is a higher-order function in Kotlin?

21. What is the syntax for a lambda expression in Kotlin?

22. How does the when expression differ from switch in Java?

23. How do you create a range in Kotlin?

24. What is the benefit of named arguments in Kotlin function calls?

25. Explain function types in Kotlin and how to use them as parameters and return values.

26. How do you create extension functions and what are their limitations and best practices?

27. Explain lambda syntax in Kotlin including it parameter, trailing lambdas, and capturing variables.

28. How do you use when expressions in Kotlin for different types of conditions and pattern matching?

29. What are inline functions in Kotlin and when should you use them?

30. Explain the different loop constructs in Kotlin including for, while, and repeat.

31. Explain Unit, Nothing, and single-expression functions in Kotlin.

32. What is tail recursion in Kotlin and how does the tailrec modifier optimize recursive functions?

33. How do you declare a basic class in Kotlin?

34. What is a primary constructor in Kotlin?

35. What methods does the Kotlin compiler automatically generate for data classes?

36. What is the purpose of sealed classes in Kotlin?

37. What is an object declaration in Kotlin?

38. What is a companion object in Kotlin?

39. What is the default visibility modifier in Kotlin?

40. How do you make a class inheritable in Kotlin?

41. Explain how properties work in Kotlin including getters, setters, and backing fields.

42. What are data classes and when should you use them? What are their requirements?

43. How do sealed classes work with when expressions and why are they useful for representing state?

44. Explain companion objects, how they differ from Java static members, and common use cases.

45. Explain primary and secondary constructors, init blocks, and the order of initialization in Kotlin.

46. How do interfaces work in Kotlin and how do they differ from abstract classes?

47. What are object expressions (anonymous objects) and when should you use them?

48. How does Kotlin support the delegation pattern with the by keyword for class and property delegation?

49. Explain the difference between nested classes and inner classes in Kotlin.

50. What are the main collection interfaces in Kotlin?

51. How do you create an immutable list in Kotlin?

52. What does the map function do on collections?

53. What does the filter function return?

54. What is the main advantage of using Sequences over Collections for chained operations?

55. What is the difference between let and apply scope functions?

56. What is the difference between reduce and fold operations?

57. Which function would you use to group collection elements by a key?

58. Explain the difference between map, flatMap, and flatten with examples of when to use each.

59. Compare all five scope functions (let, run, with, apply, also) and explain when to use each.

60. Explain when and why you should use Sequences instead of regular collections for better performance.

61. Explain the difference between mutable and immutable collections and when to use each.

62. How do you build efficient collection transformation pipelines in Kotlin?

63. Explain the associate, associateBy, and associateWith functions for creating Maps from collections.

64. Explain partition, zip, and chunked functions and their use cases.

65. What are the performance characteristics of List, Set, and Map operations and how to choose the right collection?

66. What are Coroutines in Kotlin?

67. What does the suspend modifier on a function mean?

68. What is the difference between launch and async coroutine builders?

69. What is Flow in Kotlin Coroutines?

70. What does the lazy delegate do in Kotlin?

71. What is the difference between 'out' and 'in' variance modifiers in Kotlin generics?

72. What does the reified keyword do with inline functions?

73. What is the main difference between StateFlow and SharedFlow?

74. Explain structured concurrency in Kotlin Coroutines and how it helps manage coroutine lifecycle.

75. Explain common Flow operators and when to use each for transforming asynchronous streams.

76. Explain built-in property delegates in Kotlin including lazy, observable, and vetoable.

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