Guide
KOTLIN INTERVIEW Qs
Technical questions and model answers for interviewing Kotlin developers. Covers coroutines, null safety, DSLs, and KMP.
Last updated: May 2026
How does Kotlin's null safety differ from Java's?
Kotlin distinguishes nullability at the type system level. String is non-null, String? is nullable. Operators like ?. (safe call), ?: (elvis), and !! (non-null assertion) let you eliminate NPE risk at compile time. Java introduced Optional in Java 8, but it lacks language-level enforcement.
Explain the difference between Coroutines and RxJava
Coroutines are lightweight threads supported at the language level (Kotlin stdlib), letting you write async code that looks sequential without callback hell. RxJava is powerful but has a steep learning curve and tends toward boilerplate. For new projects, Coroutines + Flow are recommended.
What is a Kotlin DSL? Give a practical example
A DSL is a concise syntax designed for a specific domain. In Kotlin, you build them with higher-order functions and lambdas with receiver (T.() -> Unit). Examples include Gradle Kotlin DSL, Jetpack Compose UI declarations, and Anko (deprecated). Using receiver lambdas with @DslMarker creates type-safe, misuse-resistant DSLs.
What are the benefits and limitations of Kotlin Multiplatform?
Benefits: Share business logic across iOS/Android while keeping UI native to each platform. Unlike Flutter or React Native, you fully retain native performance and look-and-feel. Limitations: UI layer sharing is still experimental (Compose Multiplatform), third-party library compatibility can be challenging, and build times may increase.
What's the difference between sealed class and enum class?
An enum class is a set of constants with only single instances. A sealed class defines a restricted class hierarchy where each subclass can have its own state and behavior. Both enable exhaustive checking in when expressions, and sealed classes are widely used for result types (Success/Error/Loading).
What are the benefits of delegation in Kotlin?
Kotlin's by keyword lets you implement delegation concisely instead of inheritance. This practices composition over inheritance, lowering coupling while extending functionality. Example: class MyCollection<T>(val inner: MutableList<T>) : MutableList<T> by inner
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