Enum entries iteration in Kotlin - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to print all enum entries using a for loop.

Kotlin

enum class Color { RED, GREEN, BLUE }

fun main() {
    for (color in Color.[1]) {
        println(color)
    }
}

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

Avalues()

Bentries()

Call()

Dlist()

Attempts:

3 left

💡 Hint

Common Mistakes

Using entries() which does not exist for enums in Kotlin.

Trying to call all() or list() which are not valid enum functions.

The correct way to iterate over all enum entries in Kotlin is to use the values() function.

2fill in blank

medium

Complete the code to get the number of entries in the enum.

Kotlin

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

fun main() {
    val count = Direction.[1].size
    println("Number of directions: $count")
}

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

Alist()

Ball()

Centries()

Dvalues()

Attempts:

3 left

💡 Hint

Common Mistakes

Using entries() which is not a Kotlin enum function.

Trying to get size directly from the enum class.

The values() function returns an array of all enum entries, so you can get the size from it.

3fill in blank

hard

Fix the error in the code to iterate over enum entries correctly.

Kotlin

enum class Status { ON, OFF }

fun main() {
    for (s in Status.[1]) {
        println(s)
    }
}

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

Aall()

Bvalues()

CgetValues()

Dentries

Attempts:

3 left

💡 Hint

Common Mistakes

Omitting parentheses after values.

Using entries or all which are not valid.

The correct function to get all enum entries is values(), with parentheses.

4fill in blank

hard

Fill both blanks to create a map of enum names to their ordinal values.

Kotlin

enum class Level { LOW, MEDIUM, HIGH }

fun main() {
    val map = Level.[1].associateBy([2]) { it.ordinal }
    println(map)
}

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

Avalues()

Bname

Cit.name

Dentries()

Attempts:

3 left

💡 Hint

Common Mistakes

Using entries() which is not valid.

Using name instead of it.name inside the lambda.

Use values() to get all entries, and it.name to get the name of each enum entry.

5fill in blank

hard

Fill all three blanks to filter enum entries with ordinal greater than 0 and print their names.

Kotlin

enum class Mode { BASIC, ADVANCED, EXPERT }

fun main() {
    val filtered = Mode.[1].filter { it.ordinal [2] 0 }
    for (m in filtered) {
        println(m[3])
    }
}

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

Avalues()

B>

C.name

Dentries()

Attempts:

3 left

💡 Hint

Common Mistakes

Using entries() which is invalid.

Using < instead of > in the filter.

Printing m instead of m.name.

Use values() to get all entries, filter with > 0, and print the name property.

Practice

1. What does EnumName.values() return in Kotlin?

easy

A. An array of all enum entries in the order they are declared

B. A list of enum names as strings

C. The first enum entry only

D. A map of enum entries to their ordinal values

Solution

1. Step 1: Understand the purpose of values()

   The values() function returns all enum entries as an array in the order they are declared.

2. Step 2: Compare options with this behavior

   Only An array of all enum entries in the order they are declared correctly describes this behavior; others describe different data types or partial data.

3. Final Answer:

   An array of all enum entries in the order they are declared -> Option A

4. Quick Check:

   EnumName.values() returns all entries [OK]

Hint: Remember: values() gives all enum entries as an array [OK]

Common Mistakes:

• Thinking values() returns strings instead of enum objects
• Assuming values() returns only one entry
• Confusing values() with valueOf()

2. Which of the following is the correct syntax to iterate over all entries of an enum Color in Kotlin?

easy

A. for (c in Color.values()) { println(c) }

B. for (c in Color) { println(c) }

C. for (c in Color.entries()) { println(c) }

D. for (c in Color.all()) { println(c) }

Solution

1. Step 1: Recall the correct method to get enum entries

   In Kotlin, values() returns all enum entries as an array.

2. Step 2: Check each option's syntax

   The correct syntax is for (c in Color.values()) { println(c) }, which uses Color.values() correctly in a for loop. The other options use invalid syntax: iterating directly over Color, or non-existent methods like entries() or all().

3. Final Answer:

   for (c in Color.values()) { println(c) } -> Option A

4. Quick Check:

   Use values() to loop enums [OK]

Hint: Use EnumName.values() to loop enums [OK]

Common Mistakes:

• Trying to loop directly over enum class without values()
• Using non-existent methods like entries() or all()
• Missing parentheses after values()

3. Given the enum:

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

What is the output of this code?

for (d in Direction.values()) {
    print(d.name.first())
}

medium

A. Direction.NORTHDirection.EASTDirection.SOUTHDirection.WEST

B. north east south west

C. NESW

D. N E S W

Solution

1. Step 1: Understand the loop and print statement

   The loop goes through all enum entries: NORTH, EAST, SOUTH, WEST. For each, it prints the first character of the name.

2. Step 2: Determine printed characters

   First letters are 'N', 'E', 'S', 'W'. They are printed without spaces or newlines.

3. Final Answer:

   NESW -> Option C

4. Quick Check:

   First letters combined = NESW [OK]

Hint: Check what exactly is printed inside the loop [OK]

Common Mistakes:

• Assuming spaces or newlines are printed
• Printing full names instead of first letters
• Confusing enum name with enum value

4. What is wrong with this Kotlin code snippet?

enum class Status { STARTED, RUNNING, FINISHED }

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

medium

A. The loop variable must be declared as val

B. Enums cannot be iterated in Kotlin

C. The enum class must be declared inside a function

D. Missing call to values() to get enum entries

Solution

1. Step 1: Identify how to iterate enums in Kotlin

   Enums cannot be iterated directly; you must use Status.values() to get all entries.

2. Step 2: Check the code for missing values()

   The code tries to loop over Status directly, which is invalid syntax.

3. Final Answer:

   Missing call to values() to get enum entries -> Option D

4. Quick Check:

   Use Enum.values() to iterate enums [OK]

Hint: Always use values() to loop enums [OK]

Common Mistakes:

• Trying to loop enum class directly without values()
• Thinking enums are iterable by default
• Adding unnecessary val in loop declaration

5. You have this enum:

enum class Level(val difficulty: Int) {
    EASY(1), MEDIUM(2), HARD(3)
}

How do you create a map from each enum entry to its difficulty using iteration?

hard

A. val map = Level.values().map { it.difficulty }

B. val map = Level.values().associateWith { it.difficulty }

C. val map = Level.associate { it to it.difficulty }

D. val map = Level.values().associateBy { it.difficulty }

Solution

1. Step 1: Understand the goal

   We want a map where keys are enum entries and values are their difficulty.

2. Step 2: Use values() and associateWith

   Level.values() gives all entries; associateWith maps each entry to a value.

3. Step 3: Check options

   val map = Level.values().associateWith { it.difficulty } correctly uses associateWith { it.difficulty }. val map = Level.associate { it to it.difficulty } is invalid because Level is a class, not a collection. val map = Level.values().map { it.difficulty } returns a list, not a map. val map = Level.values().associateBy { it.difficulty } maps difficulty to enum, reversing keys and values.

4. Final Answer:

   val map = Level.values().associateWith { it.difficulty } -> Option B

5. Quick Check:

   Use values() + associateWith for map [OK]

Hint: Use values().associateWith { } to map enums [OK]

Common Mistakes:

• Trying to call associate on enum class directly
• Using map() instead of associateWith() for key-value pairs
• Confusing associateBy() which reverses keys and values