Top 100 Kotlin Interview Questions & Answers (2026)

01 What is Kotlin? 02 What is the difference between val and var in Kotlin? 03 How do you declare a nullable variable in Kotlin? 04 What is the safe call operator (?.) in Kotlin? 05 What is the Elvis operator (?:) in Kotlin? 06 What is the !! operator in Kotlin? 07 What is string interpolation in Kotlin? 08 How do you declare a function in Kotlin? 09 What is the Unit type in Kotlin? 10 What is a data class in Kotlin? 11 What is an object declaration in Kotlin? 12 What is a companion object in Kotlin? 13 What is the difference between == and === in Kotlin? 14 What is the when expression in Kotlin? 15 What is a sealed class in Kotlin? 16 What is the open keyword in Kotlin? 17 How is a primary constructor defined in Kotlin? 18 What is the init block in Kotlin? 19 What is an interface in Kotlin? 20 What is a lambda expression in Kotlin? 21 What is a higher-order function in Kotlin? 22 What is an extension function in Kotlin? 23 What does the let scope function do in Kotlin? 24 What does the apply scope function do in Kotlin? 25 What is a range in Kotlin? 26 What is a default parameter in Kotlin? 27 What is a named argument in Kotlin? 28 What does the Any type represent in Kotlin? 29 What is the Nothing type in Kotlin? 30 What is destructuring declaration in Kotlin? 31 What are Kotlin's visibility modifiers? 32 What is the is operator in Kotlin? 33 What is an enum class in Kotlin? 34 What does the also scope function do in Kotlin? 35 What does the run scope function do in Kotlin? 36 What does the with scope function do in Kotlin? 37 How do you create a list in Kotlin? 38 What is a Map in Kotlin? 39 What is the it keyword in Kotlin lambdas?

01 What are Kotlin Coroutines? 02 What is a suspend function in Kotlin? 03 What is the difference between launch and async in Kotlin coroutines? 04 What are the main Coroutine Dispatchers in Kotlin? 05 What is Kotlin Flow? 06 What is StateFlow in Kotlin? 07 What is SharedFlow in Kotlin? 08 What is by lazy in Kotlin? 09 What is property delegation in Kotlin? 10 What is an inline function in Kotlin? 11 What is a reified type parameter in Kotlin? 12 What is the filter function in Kotlin collections? 13 What does the map function do in Kotlin collections? 14 What does flatMap do in Kotlin? 15 What is a Sequence in Kotlin and how does it differ from a List? 16 What is groupBy in Kotlin? 17 What is the fold function in Kotlin? 18 What is structured concurrency in Kotlin? 19 What is withContext in Kotlin coroutines? 20 What is SupervisorJob in Kotlin coroutines? 21 What is the @JvmStatic annotation in Kotlin? 22 What is operator overloading in Kotlin? 23 What is the Delegates.observable in Kotlin? 24 What is a type alias in Kotlin? 25 What is the @JvmOverloads annotation in Kotlin? 26 What is the reduce function in Kotlin? 27 What is the partition function in Kotlin? 28 What is associateBy in Kotlin? 29 What is takeIf in Kotlin? 30 What is zip in Kotlin collections? 31 What is the chunked function in Kotlin? 32 What is the difference between List and Array in Kotlin? 33 What is coroutineScope in Kotlin and how does it differ from GlobalScope? 34 What is lazy thread safety mode in Kotlin?

01 What is covariance (out) in Kotlin generics? 02 What is contravariance (in) in Kotlin generics? 03 What is a star projection in Kotlin generics? 04 What is a value class (inline class) in Kotlin? 05 What is a Kotlin DSL? 06 What is a function type with receiver in Kotlin? 07 What is the crossinline modifier in Kotlin? 08 What is the noinline modifier in Kotlin? 09 What is a Channel in Kotlin coroutines? 10 What is a Mutex in Kotlin coroutines? 11 What is CoroutineExceptionHandler in Kotlin? 12 What is Kotlin Multiplatform (KMP)? 13 What is the expect/actual mechanism in Kotlin Multiplatform? 14 What is the difference between abstract class and interface in Kotlin? 15 What is the internal visibility modifier in Kotlin? 16 What is the tailrec modifier in Kotlin? 17 What is SharingStarted in Kotlin Flow? 18 What is Flow.combine() in Kotlin? 19 What is Flow.stateIn() in Kotlin? 20 What is the buildList function in Kotlin? 21 How does Kotlin handle Java interoperability with nullable types? 22 What is an object expression (anonymous object) in Kotlin? 23 What is the contract in Kotlin? 24 What is Flow.catch in Kotlin? 25 What is the difference between hot and cold flows in Kotlin? 26 What is inline class used for vs type alias in Kotlin? 27 What is Jetpack Compose and how does it relate to Kotlin?