Kotlin Interview Questions (60+) Guide

How to Use This Guide

Answer each aloud in 60 seconds: concept plus one code snippet plus where you used it. Match each group to its lesson above.

Basics and Syntax (12)

• val vs var; when to use each?
• Type inference vs dynamic typing?
• String templates and raw strings?
• Ranges: .. vs until vs downTo?
• if/when as expressions?
• Nothing, Unit and Any types?

Null Safety (10)

• String vs String? and platform types?
• ?. vs ?: vs !! vs let?
• Safe casts with as? and smart casts?
• How do you handle Java APIs returning null?

Functions and OOP (14)

• Default plus named arguments vs overloads?
• Lambdas, trailing lambdas, higher-order functions?
• Extension functions and their limits?
• data class generated members; copy semantics?
• object vs companion object?
• open classes, sealed classes, exhaustive when?
• let/apply/also/run/with differences?

Collections and Coroutines (14)

• Immutable vs mutable collections?
• filter/map/firstOrNull patterns?
• Sequences vs lists for big data?
• launch vs async; suspend functions?
• Dispatchers.IO vs Default vs Main?
• Flow vs StateFlow vs SharedFlow?
• Structured concurrency and scopes?

Spring, Android and Practical (12+)

• @field:NotBlank and no-arg plugin why?
• Constructor injection with val?
• Compose state and recomposition?
• MockK coEvery and runTest?
• Java interop annotations you use?
• Describe your Kotlin project architecture end to end.

Key Points

• Always answer with concept plus snippet plus project.
• Null safety and coroutines decide most Kotlin interviews.
• Keep a GitHub repo to show, not just tell.