Elvis operator (?:) for default values in Kotlin - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this Kotlin code using the Elvis operator?

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

Kotlin

val name: String? = null
val displayName = name ?: "Guest"
println(displayName)

A Guest

B null

C name

D Compilation error

💡 Hint

The Elvis operator returns the left value if it is not null; otherwise, it returns the right value.

Since 'name' is null, the Elvis operator returns the default value "Guest".

❓ Predict Output

intermediate

What does this Kotlin code print with a non-null value and Elvis operator?

Look at this Kotlin code. What will be the output?

Kotlin

val input: String? = "Hello"
val result = input ?: "Default"
println(result)

A Default

B null

C Compilation error

D Hello

💡 Hint

The Elvis operator returns the left value if it is not null.

Since 'input' is "Hello" (not null), the Elvis operator returns "Hello".

❓ Predict Output

advanced

What is the output of this Kotlin code with nested Elvis operators?

Analyze this Kotlin code snippet. What will be printed?

Kotlin

val a: String? = null
val b: String? = null
val c = a ?: b ?: "Fallback"
println(c)

A a

B null

C Fallback

D Compilation error

💡 Hint

Elvis operators can be chained to provide multiple fallback values.

Both 'a' and 'b' are null, so the chained Elvis operators return "Fallback".

❓ Predict Output

advanced

What error or output does this Kotlin code produce?

Consider this Kotlin code. What will happen when it runs?

Kotlin

val number: Int? = null
val result = number ?: throw IllegalArgumentException("Number required")
println(result)

A Prints null

B Throws IllegalArgumentException with message "Number required"

C Prints 0

D Compilation error

💡 Hint

The Elvis operator can throw an exception if the left side is null.

Since 'number' is null, the Elvis operator throws the specified exception.

🧠 Conceptual

expert

How many items are in the resulting list after applying this Kotlin code with Elvis operator?

Given this Kotlin code, how many elements does the list 'results' contain after execution?

Kotlin

val inputs: List<String?> = listOf("A", null, "B", null, "C")
val results = inputs.map { it ?: "Unknown" }

A 5

B 3

C 2

D 0

💡 Hint

The map function keeps the list size the same, replacing nulls with "Unknown".

The map transforms each element, replacing nulls with "Unknown", but the list size remains 5.