Why immutable collections are default in Kotlin - Test Your Understanding

Practice - 5 Tasks

1fill in blank

easy

Complete the code to create an immutable list in Kotlin.

Kotlin

val numbers = listOf[1](1, 2, 3, 4, 5)

Drag options to blanks, or click blank then click option'

A<Any>

B<Int>

C(nothing)

D<Number>

Attempts:

3 left

💡 Hint

Common Mistakes

Using mutableListOf instead of listOf

Adding parentheses incorrectly

In Kotlin, listOf creates an immutable list by default.

2fill in blank

medium

Complete the code to try adding an element to an immutable list and see the error.

Kotlin

val fruits = listOf("Apple", "Banana")
fruits.[1]("Cherry")

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Aadd

Bappend

Cpush

Dinsert

Attempts:

3 left

💡 Hint

Common Mistakes

Using methods like append or push which don't exist in Kotlin lists

Trying to modify an immutable list directly

The add function is not available on immutable lists, so this code will cause an error.

3fill in blank

hard

Fix the error by choosing the correct mutable collection type to allow adding elements.

Kotlin

val fruits = [1]("Apple", "Banana")
fruits.add("Cherry")

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AmutableListOf

BlistOf

CsetOf

DmapOf

Attempts:

3 left

💡 Hint

Common Mistakes

Using listOf which is immutable

Using setOf or mapOf which are different collection types

Using mutableListOf creates a list that can be changed, so add works.

4fill in blank

hard

Fill both blanks to create an immutable map and access a value safely.

Kotlin

val capitals = [1]("France" to "Paris", "Japan" to "Tokyo")
val capital = capitals.[2]("France")

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AmapOf

Bget

CmutableMapOf

Dput

Attempts:

3 left

💡 Hint

Common Mistakes

Using mutableMapOf which creates a mutable map

Using put which adds or updates entries, not retrieves

mapOf creates an immutable map, and get retrieves a value by key.

5fill in blank

hard

Fill all three blanks to filter an immutable list and create a new list with only even numbers.

Kotlin

val numbers = listOf(1, 2, 3, 4, 5, 6)
val evens = numbers.[1] { it [2] 2 [3] 0 }

Drag options to blanks, or click blank then click option'

Afilter

B%

C==

Dmap

Attempts:

3 left

💡 Hint

Common Mistakes

Using map instead of filter which transforms elements

Using incorrect comparison operators

filter creates a new list with elements matching the condition. The condition checks if the number modulo 2 equals 0, meaning it's even.