Kotlin interview essentials

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The Kotlin topics interviews ask about most: null safety, special class types, scope functions, coroutines and Flow.

1. val/var, null safety & the type system

2. data, sealed, object, enum — when to use which

3. Scope functions & extension functions

4. Coroutines: suspend, scopes, dispatchers

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5. Flow, StateFlow, SharedFlow — hot vs cold

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🎯 Stage assignment

Stage project — "the bank domain in Kotlin" (2-3 hours).

In Kotlin Playground or an empty project, write a single file containing:

Account, Card and Transaction models — data classes with deliberate nullability.
A sealed interface TransferResult and an exhaustive when handling it.
Two suspend functions (balance + history), called in parallel with async and timed.
A simple "ViewModel" simulation with MutableStateFlow<UiState>: state transitions via update { it.copy(...) }.
One extension function (maskPan) and a few scope functions.

Done when: the file runs and every construct carries a "why I chose this" comment. This file becomes your reference point in later stages.