Safe call operator (?.) in Kotlin - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to safely access the length of the string variable.

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 the regular dot operator (.) causes a crash if the object is null.

Using the not-null assertion (!!.) is unsafe and can throw exceptions.

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

2fill in blank

medium

Complete the code to safely call the function toUpperCase() on a nullable string.

Kotlin

val upper = text[1]toUpperCase()

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

A?:

B.

C!!.

D?.

Attempts:

3 left

💡 Hint

Common Mistakes

Using the regular dot operator (.) causes a null pointer exception if text is null.

Using the not-null assertion (!!.) can crash the program if text is null.

The safe call operator ?. calls the function only if text is not null, otherwise returns null.

3fill in blank

hard

Fix the error in the code by safely accessing the property length of a nullable string.

Kotlin

val len = nullableString[1]length

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

A?.

B!!.

C.

D?:

Attempts:

3 left

💡 Hint

Common Mistakes

Using the regular dot operator (.) causes a null pointer exception.

Using the not-null assertion (!!.) can cause a crash if the value is null.

The safe call operator ?. avoids exceptions by returning null if nullableString is null.

4fill in blank

hard

Fill both blanks to safely call substring on a nullable string and provide a default empty string if null.

Kotlin

val result = nullableStr[1]substring(0, 3) [2] ""

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

A?.

B?:

C!!.

D.

Attempts:

3 left

💡 Hint

Common Mistakes

Using the not-null assertion (!!.) instead of safe call.

Not providing a default value for null cases.

Use ?. to safely call substring only if nullableStr is not null, and ?: to provide a default empty string if it is null.

5fill in blank

hard

Fill all three blanks to safely access the length of a nullable string's trimmed version, or return 0 if null.

Kotlin

val length = nullableStr[1]trim()[2]length [3] 0

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

A?.

B?:

D.

Attempts:

3 left

💡 Hint

Common Mistakes

Using safe call before length unnecessarily.

Not providing a default value for null cases.

First, safely call trim() with ?.. Then access length with a regular dot because trim() returns a non-null string. Finally, use ?: to return 0 if the whole expression is null.