Elvis operator deep usage in Kotlin - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Elvis operator with nested nullables

What is the output of this Kotlin code snippet?

Kotlin

val a: String? = null
val b: String? = "Hello"
val c: String? = null

val result = a ?: b ?: c ?: "Default"
println(result)

A null

B Default

C Hello

D Compilation error

💡 Hint

The Elvis operator returns the first non-null value from left to right.

The expression evaluates from left to right: 'a' is null, so it checks 'b' which is "Hello" (non-null), so it returns "Hello".

❓ Predict Output

intermediate

Elvis operator with function calls

What will be printed by this Kotlin code?

Kotlin

fun getName(): String? = null
fun getDefaultName(): String = "Guest"

val name = getName() ?: getDefaultName()
println(name)

A null

B Guest

C Compilation error

D getDefaultName

💡 Hint

Elvis operator calls the right side only if the left side is null.

getName() returns null, so Elvis operator evaluates getDefaultName() which returns "Guest".

❓ Predict Output

advanced

Elvis operator with smart casting and let

What is the output of this Kotlin code?

Kotlin

val input: String? = "Kotlin"

val length = input?.let { it.length } ?: -1
println(length)

A 6

B -1

C null

D Compilation error

💡 Hint

The safe call with let executes only if input is not null.

input is "Kotlin" (not null), so let returns length 6, Elvis operator returns 6.

❓ Predict Output

advanced

Elvis operator with multiple nullable types and side effects

What will be printed by this Kotlin code?

Kotlin

var count = 0

fun getFirst(): String? {
    count++
    return null
}

fun getSecond(): String? {
    count++
    return "Second"
}

val result = getFirst() ?: getSecond() ?: "Default"
println("$result $count")

A Default 1

B Second 1

C Default 2

D Second 2

💡 Hint

Elvis operator evaluates left to right and stops at first non-null.

getFirst() returns null and increments count to 1, getSecond() returns "Second" and increments count to 2, so result is "Second" and count is 2.

❓ Predict Output

expert

Complex Elvis operator with nested expressions and nullables

What is the output of this Kotlin code?

Kotlin

data class User(val name: String?, val nickname: String?)

fun getUser(): User? = User(null, "Nick")

val displayName = getUser()?.name ?: getUser()?.nickname ?: "Unknown"
println(displayName)

A Nick

B Unknown

C Compilation error

D null

💡 Hint

Elvis operator chains check for non-null values from left to right.

getUser() returns User(null, "Nick"). The first call getUser()?.name is null, so Elvis operator checks getUser()?.nickname which is "Nick".