Map creation (mapOf, mutableMapOf) in Kotlin - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this Kotlin code?

Consider the following Kotlin code snippet. What will be printed when it runs?

Kotlin

val map = mapOf("a" to 1, "b" to 2, "c" to 3)
println(map["b"])

A null

B b

C 2

D 1

💡 Hint

Look at how the map is created and how the value is accessed by key.

The map contains keys "a", "b", and "c" with values 1, 2, and 3 respectively. Accessing map["b"] returns 2.

❓ Predict Output

intermediate

What happens when you modify a mutable map?

What will be the output of this Kotlin code?

Kotlin

val mutableMap = mutableMapOf("x" to 10, "y" to 20)
mutableMap["x"] = 15
println(mutableMap["x"])

A 15

B null

C 20

D 10

💡 Hint

mutableMapOf allows changing values after creation.

The mutable map allows updating the value for key "x" from 10 to 15, so printing mutableMap["x"] outputs 15.

❓ Predict Output

advanced

What is the output of this Kotlin code with mapOf and null key?

Analyze this Kotlin code and select the output it produces.

Kotlin

val map = mapOf(null to "empty", "key" to "value")
println(map[null])

A empty

B null

C value

D Compilation error

💡 Hint

Kotlin maps can have null keys unless specified otherwise.

The map contains a null key with value "empty". Accessing map[null] returns "empty".

❓ Predict Output

advanced

What error does this Kotlin code raise?

What error will this Kotlin code produce when run?

Kotlin

val map = mapOf("a" to 1, "b" to 2)
map["a"] = 3

A UnsupportedOperationException

B Unresolved reference: set

C No error, prints 3

D NullPointerException

💡 Hint

mapOf creates an immutable map, so you cannot change values.

Trying to assign a value to a key in an immutable map results in a compilation error: Unresolved reference: set.

🧠 Conceptual

expert

How many entries does this Kotlin map contain?

Given the following Kotlin code, how many key-value pairs does the map contain?

Kotlin

val map = mutableMapOf("one" to 1, "two" to 2)
map.put("three", 3)
map["two"] = 22
map.remove("one")

A 3

B 4

C 1

D 2

💡 Hint

Consider all insertions, updates, and removals carefully.

Initially, the map has 2 entries. Adding "three" to 3 makes 3 entries. Updating "two" does not change count. Removing "one" leaves 2 entries.