Kotlineasy

Explain null safety in Kotlin.

Answer

Kotlin types are non‑null by default. To allow null you mark a type with ?. Safe calls (?.), the Elvis operator (?:), and scope functions like let help handle nullable values without NPEs. !! forces a non‑null assertion and can throw.

val name: String? = null
val length = name?.length ?: 0
println(length)

Advanced answer

Deep dive

Expanding on the short answer — what usually matters in practice:

Context (tags): null-safety, nullable, elvis-operator, kotlin
JVM: memory (heap/stack), GC, and what drives latency.
Contracts: equals/hashCode/toString, mutability and consequences.
Performance: boxing, allocations, collections, inlining.
Explain the "why", not just the "what" (intuition + consequences).
Trade-offs: what you gain/lose (time, memory, complexity, risk).
Edge cases: empty inputs, large inputs, invalid inputs, concurrency.

Examples

Here’s an additional example (building on the short answer):

val name: String? = null
val length = name?.length ?: 0
println(length)

Common pitfalls

Too generic: no concrete trade-offs or examples.
Mixing average-case and worst-case (e.g., complexity).
Ignoring constraints: memory, concurrency, network/disk costs.

Interview follow-ups

When would you choose an alternative and why?
What production issues show up and how do you diagnose them?