Why null safety is Kotlin's defining feature - Test Your Understanding

Practice - 5 Tasks

1fill in blank

easy

Complete the code to declare a nullable variable in Kotlin.

Kotlin

var name: String[1] = null

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

A*

B!

C?

D#

Attempts:

3 left

💡 Hint

Common Mistakes

Using '!' instead of '?' to mark nullable types.

In Kotlin, adding ? after a type makes it nullable, allowing it to hold null.

2fill in blank

medium

Complete the code to safely access the length of a nullable string.

Kotlin

val length = name[1]length

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.

The safe call operator ?. allows accessing a property only if the object is not null.

3fill in blank

hard

Fix the error in the code to throw an exception if the nullable variable is null.

Kotlin

val nonNullName = name[1]

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

A?

B!!

C?.

D?:

Attempts:

3 left

💡 Hint

Common Mistakes

Using '?' which allows nulls without exception.

The !! operator asserts that the value is not null and throws an exception if it is.

4fill in blank

hard

Fill both blanks to provide a default value if the nullable variable is null.

Kotlin

val displayName = name [1] "Unknown"

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

A?:

B==

C?

D!!

Attempts:

3 left

💡 Hint

Common Mistakes

Using '!!' which throws instead of providing a default.

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

5fill in blank

hard

Fill all three blanks to filter a list of nullable strings and print their lengths safely.

Kotlin

val names: List<String?> = listOf("Anna", null, "Bob")
val lengths = names.filterNotNull().map { it[1]length }
lengths.forEach { println(it[2]toString()[3]) }

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

A.

B+

C()

D?.

Attempts:

3 left

💡 Hint

Common Mistakes

Using safe call operator after filtering nulls, which is unnecessary.

After filtering nulls, it.length accesses length safely. Then println(it + "") prints the length as string.