Enum entries iteration in Kotlin - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of iterating enum entries with for loop

What is the output of this Kotlin code that iterates over enum entries using a for loop?

Kotlin

enum class Color { RED, GREEN, BLUE }

fun main() {
    for (color in Color.values()) {
        println(color)
    }
}

A red\ngreen\nblue

B RED\nGREEN\nBLUE

C Color.RED\nColor.GREEN\nColor.BLUE

D RED GREEN BLUE

💡 Hint

Remember that printing enum entries calls their toString() method which returns the name by default.

The values() function returns all enum entries. Printing each entry prints its name in uppercase as declared.

❓ Predict Output

intermediate

Output of iterating enum entries with forEach and lambda

What will this Kotlin code print when iterating enum entries with forEach and a lambda?

Kotlin

enum class Direction { NORTH, EAST, SOUTH, WEST }

fun main() {
    Direction.values().forEach { println(it.name.lowercase()) }
}

A north\neast\nsouth\nwest

B NORTH\nEAST\nSOUTH\nWEST

C Direction.NORTH\nDirection.EAST\nDirection.SOUTH\nDirection.WEST

D north east south west

💡 Hint

The name property returns the enum constant name as declared. The lowercase() function converts it to lowercase.

Each enum entry's name is converted to lowercase and printed on its own line.

🧠 Conceptual

advanced

Understanding enum entries iteration with indices

Given this Kotlin code, what is the output when iterating enum entries with their indices?

Kotlin

enum class Level { LOW, MEDIUM, HIGH }

fun main() {
    Level.values().forEachIndexed { index, level ->
        println("$index: $level")
    }
}

A Level.LOW: 0\nLevel.MEDIUM: 1\nLevel.HIGH: 2

B LOW: 0\nMEDIUM: 1\nHIGH: 2

C 0 LOW\n1 MEDIUM\n2 HIGH

D 0: LOW\n1: MEDIUM\n2: HIGH

💡 Hint

forEachIndexed provides the index and the element in order.

The index starts at 0 and increments by 1 for each enum entry. The output prints index and enum name separated by colon.

🔧 Debug

advanced

Identify the error in enum iteration code

What error does this Kotlin code produce when trying to iterate enum entries?

Kotlin

enum class Status { STARTED, RUNNING, FINISHED }

fun main() {
    for (s in Status) {
        println(s)
    }
}

A No error, prints STARTED RUNNING FINISHED

B Error: Missing parentheses after Status

C Error: 'Status' is not iterable

D Error: Cannot use enum class in for loop

💡 Hint

You must call values() to get an array of enum entries to iterate.

Enum classes are not directly iterable. You must use Status.values() to get the array of entries.

🚀 Application

expert

Count enum entries with a specific property

Given this enum with a property, what is the output of counting entries with isActive = true?

Kotlin

enum class TaskStatus(val isActive: Boolean) {
    TODO(true), IN_PROGRESS(true), DONE(false), CANCELLED(false)
}

fun main() {
    val activeCount = TaskStatus.values().count { it.isActive }
    println(activeCount)
}

A 2

B 4

C 3

D 1

💡 Hint

Check which enum entries have isActive set to true.

TODO and IN_PROGRESS have isActive = true, so count is 2.