Kotlin Kotlin Collections and Generics 2

Question 1

What does `associateBy` do in Kotlin collections?

Accepted Answer

Creates a Map from a collection using a key selector

Answer

Groups elements into a set

Answer

Associates two collections by index

Answer

Creates a bidirectional map

Question 2

What is the difference between `any` and `all` in Kotlin collections?

Accepted Answer

`any` returns true if at least one element matches; `all` returns true only if every element matches

Answer

`any` checks all elements, `all` checks one

Answer

They are identical

Answer

`any` works on sets, `all` works on lists

Question 3

What does `partition` do in Kotlin?

Accepted Answer

Splits a collection into two lists: matches and non-matches based on a predicate

Answer

Splits a collection into equal-sized chunks

Answer

Divides elements among multiple threads

Answer

Removes every other element

Question 4

What is the purpose of generics in Kotlin?

Accepted Answer

To enable type-safe reusable code that works with different types

Answer

To allow functions to accept any number of parameters

Answer

To make classes serializable

Answer

To avoid using nulls

Question 5

What does `out T` (covariance) mean in Kotlin generics?

Accepted Answer

T can only be produced (returned), making the generic covariant

Answer

T can only be used as a parameter type

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T must implement Comparable

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T can be mutated inside the class

Question 6

What does `in T` (contravariance) mean in Kotlin generics?

Accepted Answer

T can only be consumed (accepted as input), making the generic contravariant

Answer

T can only be produced from the class

Answer

T is an optional type

Answer

T must be nullable