Nullable types with ? suffix in Kotlin - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to declare a nullable String variable.

Kotlin

var name: String[1] = null

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

A?

B!

C(no suffix)

D*

Attempts:

3 left

💡 Hint

Common Mistakes

Using an exclamation mark instead of a question mark.

Leaving the type non-nullable and assigning null.

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.

Using just a dot which causes a compile error on nullable types.

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

3fill in blank

hard

Fix the error in the code to assign a nullable String to a non-nullable variable.

Kotlin

val nonNullName: String = name[1]

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

A!!

B?.toString()

C?

D?: ""

Attempts:

3 left

💡 Hint

Common Mistakes

Using safe call ?. which returns nullable type.

Using ?: "" which is for providing default values.

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

4fill in blank

hard

Fill both blanks to create a map of words to their lengths only if length is greater than 3.

Kotlin

val lengths = mapOf([1] to [2]).filter { it.value > 3 }

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

A"hello"

B"hello".length

C"hi"

D"hi".length

Attempts:

3 left

💡 Hint

Common Mistakes

Using a word shorter than 4 characters which will be filtered out.

Using the length property incorrectly.

The map pairs a word with its length. We use the word "hello" and its length.

5fill in blank

hard

Fill all three blanks to create a nullable variable, check if it is null, and provide a default value.

Kotlin

val input: String[1] = null
val result = input [2] "default"
println(result[3])

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

A?

B?:

C?.length

D!!

Attempts:

3 left

💡 Hint

Common Mistakes

Not marking the variable as nullable.

Using !! which throws exception if null.

Not using safe call operator before accessing length.

The variable is nullable with ?. The Elvis operator ?: provides a default if null. The safe call ?. accesses length safely.