Why enums constrain values in Kotlin - Test Your Understanding

Practice - 5 Tasks

1fill in blank

easy

Complete the code to declare an enum class named Direction.

Kotlin

enum class [1] { NORTH, SOUTH, EAST, WEST }

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

ADirection

Bdirection

CDirections

DDir

Attempts:

3 left

💡 Hint

Common Mistakes

Using lowercase names for enum classes.

Using plural form which is not declared in the code.

The enum class must be named with a capitalized identifier, here Direction, to follow Kotlin conventions.

2fill in blank

medium

Complete the code to access the enum value EAST.

Kotlin

val dir = Direction.[1]

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

Aeast

BEAST

CEast

DeAST

Attempts:

3 left

💡 Hint

Common Mistakes

Using lowercase or mixed case for enum constants.

Trying to access a non-existent enum value.

Enum constants in Kotlin are uppercase by convention, so EAST is correct.

3fill in blank

hard

Fix the error in the code to assign a valid enum value to variable dir.

Kotlin

val dir: Direction = Direction.[1]

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

ANORTH

BUP

CDOWN

DLEFT

Attempts:

3 left

💡 Hint

Common Mistakes

Using values not declared in the enum class.

Trying to assign strings or other types instead of enum constants.

Only the enum constants declared in Direction can be assigned. NORTH is valid; others are not declared.

4fill in blank

hard

Fill both blanks to create a function that returns true if the direction is WEST.

Kotlin

fun isWest(dir: Direction): Boolean = dir [1] Direction.[2]

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A==

B!=

CWEST

DEAST

Attempts:

3 left

💡 Hint

Common Mistakes

Using inequality operator instead of equality.

Comparing to the wrong enum constant.

The function compares if dir is equal to Direction.WEST using ==.

5fill in blank

hard

Fill all three blanks to create a when expression that returns a message for each direction.

Kotlin

fun directionMessage(dir: Direction): String = when(dir) {
    Direction.NORTH -> "Go [1]"
    Direction.SOUTH -> "Go [2]"
    Direction.EAST -> "Go [3]"
    else -> "Stay still"
}

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

Anorth

Bsouth

Ceast

Dwest

Attempts:

3 left

💡 Hint

Common Mistakes

Using uppercase or mixed case in the message.

Mixing up directions in the messages.

The messages correspond to the direction names in lowercase matching each enum constant.

Practice

1. Why do Kotlin enums constrain values to a fixed set?

easy

A. To prevent invalid values and reduce errors

B. To allow any value to be assigned

C. To make the code run faster

D. To increase the size of the program

Solution

1. Step 1: Understand enum purpose

   Enums define a limited set of named values to represent options clearly.

2. Step 2: Identify why limiting values helps

   Limiting values prevents invalid or unexpected inputs, reducing bugs.

3. Final Answer:

   To prevent invalid values and reduce errors -> Option A

4. Quick Check:

   Enums limit values = prevent errors [OK]

Hint: Enums fix allowed values to avoid mistakes [OK]

Common Mistakes:

• Thinking enums allow any value
• Believing enums improve speed directly
• Confusing enums with variables

2. Which of the following is the correct syntax to declare an enum in Kotlin?

easy

A. enum Direction = { NORTH, SOUTH, EAST, WEST }

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

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

D. enum Direction { NORTH; SOUTH; EAST; WEST }

Solution

1. Step 1: Recall Kotlin enum syntax

   Kotlin enums use 'enum class' followed by the name and curly braces with values separated by commas.

2. Step 2: Check each option

   enum class Direction { NORTH, SOUTH, EAST, WEST } matches correct syntax; others have wrong keywords or separators.

3. Final Answer:

   enum class Direction { NORTH, SOUTH, EAST, WEST } -> Option C

4. Quick Check:

   Correct enum syntax = enum class Direction { NORTH, SOUTH, EAST, WEST } [OK]

Hint: Remember: 'enum class Name { VALUES }' [OK]

Common Mistakes:

• Using 'class enum' instead of 'enum class'
• Separating values with semicolons
• Assigning enum like a variable

3. What will be the output of this Kotlin code?

enum class Color { RED, GREEN, BLUE }
fun main() {
    val c: Color = Color.GREEN
    println(c == Color.GREEN)
    println(c == Color.RED)
}

medium

A. false\nfalse

B. false\ntrue

C. true\ntrue

D. true\nfalse

Solution

1. Step 1: Understand enum comparison

   Enum values are compared by identity. c is assigned Color.GREEN.

2. Step 2: Evaluate println statements

   c == Color.GREEN is true; c == Color.RED is false.

3. Final Answer:

   true\nfalse -> Option D

4. Quick Check:

   Enum equality matches assigned value [OK]

Hint: Enum comparisons check exact named value [OK]

Common Mistakes:

• Assuming enums compare by string content
• Confusing true/false order
• Using == incorrectly with enums

4. Identify the error in this Kotlin enum usage:

enum class Size { SMALL, MEDIUM, LARGE }
fun main() {
    val s: Size = Size.EXTRA_LARGE
    println(s)
}

medium

A. Cannot print enum values directly

B. Size.EXTRA_LARGE does not exist in the enum

C. Enum values must be lowercase

D. Missing semicolon after enum values

Solution

1. Step 1: Check enum declaration

   Enum Size has only SMALL, MEDIUM, LARGE values defined.

2. Step 2: Analyze usage error

   Code tries to assign Size.EXTRA_LARGE which is not defined, causing error.

3. Final Answer:

   Size.EXTRA_LARGE does not exist in the enum -> Option B

4. Quick Check:

   Using undefined enum value = error [OK]

Hint: Use only defined enum values [OK]

Common Mistakes:

• Assuming enums accept any value
• Thinking semicolons are required
• Believing enum values must be lowercase

5. You want to restrict user input to only three modes: EASY, MEDIUM, HARD using Kotlin enums. Which approach best ensures invalid modes cannot be used in your program?

hard

A. Define enum class Mode { EASY, MEDIUM, HARD } and use Mode type for input

B. Use strings "EASY", "MEDIUM", "HARD" and check with if-else

C. Use integers 1, 2, 3 to represent modes without enum

D. Allow any string input and convert to uppercase

Solution

1. Step 1: Understand enum benefits for input restriction

   Enums limit values to a fixed set, preventing invalid inputs.

2. Step 2: Compare approaches

   Define enum class Mode { EASY, MEDIUM, HARD } and use Mode type for input uses enum type, ensuring only EASY, MEDIUM, HARD are valid. Others allow invalid inputs or require manual checks.

3. Final Answer:

   Define enum class Mode { EASY, MEDIUM, HARD } and use Mode type for input -> Option A

4. Quick Check:

   Enums enforce valid values automatically [OK]

Hint: Use enums to restrict allowed options [OK]

Common Mistakes:

• Using strings without validation
• Using integers without clear meaning
• Allowing any input without checks