Kotlin Kotlin Collections and Generics

Question 1

Which Kotlin collection is immutable by default?

Accepted Answer

List

Answer

In Kotlin, `List` is a read-only interface that does not expose mutation methods; `MutableList` is its mutable counterpart.

Question 2

How do you create a mutable list in Kotlin?

Accepted Answer

mutableListOf()

Answer

`mutableListOf()` creates a `MutableList<T>` backed by an `ArrayList`, allowing add, remove, and update operations.

Question 3

What does the `groupBy` function do in Kotlin?

Accepted Answer

Groups elements into a map by a key selector function

Answer

`groupBy` returns a `Map>` where each key maps to a list of elements matching that key from the key selector.

Question 4

Which function returns the first element matching a predicate or null in Kotlin?

Accepted Answer

find()

Answer

`find()` returns the first element satisfying the predicate, or null if no element matches, unlike `first()` which throws if not found.

Question 5

What does `flatMap` do in Kotlin?

Accepted Answer

Maps each element and then flattens the resulting nested collections

Answer

`flatMap` applies a transform that returns a collection for each element, then flattens all results into a single list.

Kotlin Practice Test