Elvis operator (?:) for default values in Kotlin - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to assign a default value using the Elvis operator.

Kotlin

val name: String? = null
val displayName = name [1] "Guest"

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

A?:

B!!

C?.

D==

Attempts:

3 left

💡 Hint

Common Mistakes

Using '!!' which throws an exception if null.

Using '?.' which is for safe calls, not default values.

The Elvis operator ?: returns the left value if it's not null; otherwise, it returns the right value.

2fill in blank

medium

Complete the code to print a default message when the nullable variable is null.

Kotlin

fun greet(user: String?) {
    println(user [1] "Anonymous")
}

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

A!!

B?:

C?.

D==

Attempts:

3 left

💡 Hint

Common Mistakes

Using '!!' which causes an exception if null.

Using '?.' which is for safe calls, not default values.

The Elvis operator ?: provides a default value when the left side is null.

3fill in blank

hard

Fix the error in the code by using the correct operator to provide a default value.

Kotlin

val length = text?.length [1] 0

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

A==

B!!

C?.

D?:

Attempts:

3 left

💡 Hint

Common Mistakes

Using '!!' which throws an exception if null.

Using '?.' which is for safe calls, not default values.

The Elvis operator ?: returns 0 if text?.length is null.

4fill in blank

hard

Fill both blanks to create a map of words to their lengths, but only include words longer than 3 characters.

Kotlin

val words = listOf("cat", null, "elephant", "dog", "lion")
val lengths = words.associateWith { it?.length [1] 0 } .filter { it.value [2] 3 }

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

A?:

B>

C>=

D!!

Attempts:

3 left

💡 Hint

Common Mistakes

Using '!!' which throws an exception if the word is null.

Using '>=' which would include words of length 3.

Use the Elvis operator ?: to return 0 if it?.length is null (when word is null), and > to filter lengths greater than 3.

5fill in blank

hard

Fill all three blanks to create a map of uppercase words to their lengths, including only words with length greater than 3.

Kotlin

val words = listOf("apple", null, "bat", "carrot", "dog")
val result = words.associate { (it ?: "UNKNOWN")[1] to it?.length [2] 0 } .filter { it.value [3] 3 }

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

A.uppercase()

B?:

C>

D!!

Attempts:

3 left

💡 Hint

Common Mistakes

Using '!!' in the second blank, which throws an exception if word is null.

Using '>=' in the third blank, which includes length 3.

Use '.uppercase()' to convert the key to uppercase (null handled as "UNKNOWN"), the Elvis operator ?: to default length to 0 if null, and '>' to filter lengths greater than 3.