Collections (List, Map, Set) in Android Kotlin - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ ui_behavior

intermediate

What is the output of this Kotlin code using a List?

Consider this Kotlin code snippet that creates and prints a list. What will be printed?

Android Kotlin

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

A Cherry

B Apple

C Banana

D IndexOutOfBoundsException

💡 Hint

Remember that list indices start at zero.

In Kotlin, list indices start at 0, so fruits[1] accesses the second item, which is "Banana".

📝 Syntax

intermediate

What error does this Kotlin Map code produce?

Examine this Kotlin code that tries to create a map. What error will it cause?

Android Kotlin

val map = mapOf("one" to 1, "two" 2, "three" to 3)

A No error, map created successfully

B TypeError: Cannot assign Int to String

C RuntimeException: Duplicate keys

D SyntaxError: Missing 'to' keyword

💡 Hint

Check the syntax for key-value pairs in mapOf.

In Kotlin, mapOf requires key-value pairs separated by 'to'. The pair "two" 2 is missing 'to', causing a syntax error.

❓ lifecycle

advanced

What happens when you add duplicate elements to a Kotlin Set?

Given this Kotlin code, what will be the size of the set after adding duplicates?

Android Kotlin

val numbers = mutableSetOf(1, 2, 3)
numbers.add(2)
numbers.add(4)
println(numbers.size)

A 5

B 4

C 3

D RuntimeException

💡 Hint

Sets do not allow duplicate elements.

Sets only keep unique elements. Adding 2 again does not increase size. Adding 4 adds a new element. So size is 4.

🔧 Debug

advanced

Why does this Kotlin code throw an exception?

This Kotlin code tries to access a map value. Why does it throw an exception?

Android Kotlin

val map = mapOf("a" to 1, "b" to 2)
val value = map["c"]!!
println(value)

A NullPointerException because key "c" is missing and !! forces non-null

B No exception, prints 0

C KeyNotFoundException because "c" is not in map

D Compilation error due to !! operator

💡 Hint

What does the !! operator do when the value is null?

The !! operator asserts non-null. Since map["c"] returns null, !! throws NullPointerException.

🧠 Conceptual

expert

How many items are in this Kotlin collection after these operations?

What is the size of the collection after this Kotlin code runs?

Android Kotlin

val list = listOf(1, 2, 3, 4)
val set = list.toMutableSet()
set.remove(2)
set.add(5)
val map = set.associateWith { it * 2 }
println(map.size)

A 4

B 5

C 3

D 6

💡 Hint

Track each step: list to set, remove, add, then map size.

Starting with list of 4 items, converted to set (4 unique items). Remove one (2), add one (5), set size remains 4. Map keys come from set, so map size is 4.