Why enums constrain values in Kotlin - Challenge Your Understanding

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of enum usage in Kotlin

What is the output of this Kotlin code that uses an enum to restrict values?

Kotlin

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

fun main() {
    val dir = Direction.NORTH
    println("Direction is: $dir")
}

A Direction is: 0

B Direction is: North

C Direction is: NORTH

D Compilation error

💡 Hint

Remember enums print their name exactly as declared.

In Kotlin, enums print their name property by default, which is the exact uppercase string declared.

🧠 Conceptual

intermediate

Why enums restrict values

Why do enums in Kotlin constrain the possible values a variable can have?

A Because enums are mutable and can change values at runtime.

B Because enums allow any string value to be assigned.

C Because enums automatically convert values to integers.

D Because enums define a fixed set of constants, preventing invalid values.

💡 Hint

Think about how enums limit choices.

Enums define a fixed set of named constants, so variables of enum type can only hold those values, preventing invalid assignments.

🔧 Debug

advanced

Identify the error with enum assignment

What error occurs when you try to assign a value not defined in the enum?

Kotlin

enum class Color { RED, GREEN, BLUE }

fun main() {
    val c: Color = Color.YELLOW
    println(c)
}

A Compilation error: Unresolved reference: YELLOW

B Runtime error: IllegalArgumentException

C Prints 'YELLOW' without error

D Compilation error: Type mismatch

💡 Hint

Check if the enum contains the value YELLOW.

Since YELLOW is not defined in the Color enum, the compiler cannot find it, causing an unresolved reference error.

❓ Predict Output

advanced

Output when using enum ordinal

What is the output of this Kotlin code using enum ordinal values?

Kotlin

enum class Size { SMALL, MEDIUM, LARGE }

fun main() {
    val s = Size.MEDIUM
    println(s.ordinal)
}

A 1

B 2

C Compilation error

D 0

💡 Hint

Ordinal starts counting from zero.

The ordinal property returns the position of the enum constant starting at 0, so MEDIUM is at index 1.

🚀 Application

expert

Using enums to validate input

Given this Kotlin enum and function, what will be the output when calling validateDirection("UP")?

Kotlin

enum class Direction { UP, DOWN, LEFT, RIGHT }

fun validateDirection(input: String): String {
    return try {
        val dir = Direction.valueOf(input)
        "Valid direction: $dir"
    } catch (e: IllegalArgumentException) {
        "Invalid direction"
    }
}

fun main() {
    println(validateDirection("UP"))
}

A Invalid direction

B Valid direction: UP

C Compilation error

D Runtime error: NullPointerException

💡 Hint

Check if 'UP' is a valid enum constant.

The string 'UP' matches an enum constant, so valueOf succeeds and returns that enum, producing the valid message.