Extensions on built-in types in Kotlin - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to define an extension function isEven for Int that returns true if the number is even.

Kotlin

fun Int.isEven(): Boolean {
    return this [1] 2 == 0
}

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

A*

B/

C%

D+

Attempts:

3 left

💡 Hint

Common Mistakes

Using division (/) instead of modulus (%) causes wrong results.

The modulus operator (%) returns the remainder. If the remainder when divided by 2 is 0, the number is even.

2fill in blank

medium

Complete the code to define an extension function lastChar for String that returns its last character.

Kotlin

fun String.lastChar(): Char {
    return this[1]length - 1]
}

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

A<

B(

C{

D[

Attempts:

3 left

💡 Hint

Common Mistakes

Using parentheses () instead of square brackets [] for indexing.

Square brackets [] are used to access characters by index in a String.

3fill in blank

hard

Fix the error in the extension function that tries to double each element in a list of integers.

Kotlin

fun List<Int>.doubleElements(): List<Int> {
    return this.map { it [1] 2 }
}

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

A*

B+

C-

D/

Attempts:

3 left

💡 Hint

Common Mistakes

Using + instead of * results in adding 2 instead of doubling.

To double each element, multiply it by 2 using the * operator.

4fill in blank

hard

Fill both blanks to create an extension function filterShortWords for List<String> that returns words shorter than 5 characters.

Kotlin

fun List<String>.filterShortWords(): List<String> {
    return this.filter { word -> word.[1] < [2] }
}

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

Alength

B5

Ccount

Dsize

Attempts:

3 left

💡 Hint

Common Mistakes

Using count or size instead of length for strings.

Use the length property to get the number of characters in a word and compare it to 5.

5fill in blank

hard

Fill all three blanks to create an extension function toMapByFirstChar for List<String> that returns a map grouping words by their first uppercase character.

Kotlin

fun List<String>.toMapByFirstChar(): Map<Char, List<String>> {
    return this.groupBy { it[1]().[2](0) }
        .mapKeys { it.key.[3]() }
}

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

AtoUpperCase

Buppercase

Cfirst

DuppercaseChar

Attempts:

3 left

💡 Hint

Common Mistakes

Using deprecated 'toUpperCase()' instead of 'uppercase()'.

Confusing string and char uppercase functions.

Use 'uppercase()' to convert the string to uppercase, 'first' to get the first character, and 'uppercaseChar()' to convert a character to uppercase.