Variables (val, var) and null safety in Android Kotlin - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to declare a variable that can be changed later.

Android Kotlin

var name: String = "John"
name = [1]

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

A"Alice"

Bval

Cvar

Dnull

Attempts:

3 left

💡 Hint

Common Mistakes

Using val instead of a string value to assign.

Trying to assign null without making the variable nullable.

We use var to declare a variable that can change. Assigning "Alice" updates the value.

2fill in blank

medium

Complete the code to declare a constant string that cannot be changed.

Android Kotlin

val greeting: String = [1]

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

Anull

Bval

Cvar

D"Hello"

Attempts:

3 left

💡 Hint

Common Mistakes

Using var instead of val for constants.

Assigning null without nullable type.

val declares a constant. Assigning "Hello" sets the constant string value.

3fill in blank

hard

Fix the error in the code by making the variable nullable.

Android Kotlin

var age: Int = [1]
age = null

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

AInt?

B0

Cnull

Dvar

Attempts:

3 left

💡 Hint

Common Mistakes

Trying to assign null to a non-nullable type.

Using var keyword inside the assignment.

Adding ? after Int makes the variable nullable, so it can hold null.

4fill in blank

hard

Fill both blanks to declare a nullable variable and assign null to it.

Android Kotlin

var city: [1] = [2]

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

AString?

Bnull

CString

D"Paris"

Attempts:

3 left

💡 Hint

Common Mistakes

Declaring variable as non-nullable String and assigning null.

Assigning a string value instead of null.

String? makes city nullable. Assigning null is allowed then.

5fill in blank

hard

Fill all three blanks to safely print the length of a nullable string.

Android Kotlin

val length = name[1][2][3]

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

A?

B.length

C?: 0

D!!

Attempts:

3 left

💡 Hint

Common Mistakes

Using !! which throws error if null.

Not providing default value for null case.

The safe call operator ? allows access if not null, .length gets length, ?: 0 provides default if null.