Why extensions add without modifying in Kotlin - Test Your Understanding

Practice - 5 Tasks

1fill in blank

easy

Complete the code to define an extension function that adds a greeting to a String.

Kotlin

fun String.greet() = "Hello, " + [1]

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

Ait

Bself

Cthis

Dthat

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'it' or 'self' instead of 'this' inside the extension function.

The keyword this refers to the receiver object inside an extension function.

2fill in blank

medium

Complete the code to call the extension function on a String.

Kotlin

val name = "Alice"
println(name[1]())

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

A.greet()

B.greet

Cgreet()

Dgreet

Attempts:

3 left

💡 Hint

Common Mistakes

Forgetting parentheses when calling the extension function.

Extension functions are called like regular functions on the object, so parentheses are needed.

3fill in blank

hard

Fix the error in the extension function that tries to modify the original String.

Kotlin

fun String.addExclamation() {
    [1] += "!"
}

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

Aname

Bthis

Cself

Dit

Attempts:

3 left

💡 Hint

Common Mistakes

Trying to change the original String inside the extension function.

Strings are immutable in Kotlin, so you cannot modify this directly inside an extension function.

4fill in blank

hard

Fill both blanks to create an extension function that returns a new String with an exclamation mark added.

Kotlin

fun String.addExclamation() = [1] + [2]

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

Athis

B"!"

Cthis.toString()

D"?"

Attempts:

3 left

💡 Hint

Common Mistakes

Using incorrect string literals or trying to modify the original String.

The extension returns a new String by adding an exclamation mark to the original this String.

5fill in blank

hard

Fill all three blanks to create an extension function that repeats the String n times with a separator.

Kotlin

fun String.repeatWithSeparator(n: Int, sep: String) = (1..n).joinToString([1]) { [2] } + [3]

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

Asep

Bthis

C"!"

D"?"

Attempts:

3 left

💡 Hint

Common Mistakes

Using wrong separator or forgetting to use this inside the lambda.

The function joins the String repeated n times separated by sep and adds an exclamation mark at the end.