Enum with properties and methods in Kotlin - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of enum with property and method

What is the output of this Kotlin code?

Kotlin

enum class Direction(val degrees: Int) {
    NORTH(0) {
        override fun description() = "Upwards"
    },
    EAST(90) {
        override fun description() = "Rightwards"
    },
    SOUTH(180) {
        override fun description() = "Downwards"
    },
    WEST(270) {
        override fun description() = "Leftwards"
    };

    abstract fun description(): String
}

fun main() {
    val dir = Direction.EAST
    println("${dir.name} is at ${dir.degrees} degrees and means ${dir.description()}")
}

A EAST is at 90 degrees and means Rightwards

B EAST is at 90 degrees and means Upwards

C EAST is at 180 degrees and means Rightwards

D Compilation error due to abstract method

💡 Hint

Check how each enum constant overrides the abstract method description().

Each enum constant provides its own implementation of the abstract method description(). EAST returns "Rightwards" and has degrees 90.

❓ Predict Output

intermediate

Enum method call result

What does this Kotlin program print?

Kotlin

enum class Light(val duration: Int) {
    RED(30),
    GREEN(45),
    YELLOW(5);

    fun isSafeToGo() = this == GREEN
}

fun main() {
    val current = Light.YELLOW
    println(current.isSafeToGo())
}

A true

B Runtime exception

C Compilation error: missing method body

D false

💡 Hint

Check which enum constant returns true for isSafeToGo().

Only GREEN returns true for isSafeToGo(). YELLOW returns false.

🔧 Debug

advanced

Identify the error in enum with method override

This Kotlin enum tries to override a method but causes a compilation error. What is the error?

Kotlin

enum class Status {
    SUCCESS {
        override fun message() = "Operation succeeded"
    },
    FAILURE {
        override fun message() = "Operation failed"
    };

    fun message(): String = "Unknown"
}

A Cannot override non-abstract method message() without marking it abstract

B Missing semicolon after enum constants

C Abstract method message() must be declared abstract in enum

D Enum constants cannot have method bodies

💡 Hint

Check if the method message() is abstract or not.

You cannot override a non-abstract method in enum constants. To override, message() must be abstract.

❓ Predict Output

advanced

Output of enum with companion object method

What is the output of this Kotlin code?

Kotlin

enum class Planet(val mass: Double, val radius: Double) {
    EARTH(5.972e24, 6371.0),
    MARS(0.64171e24, 3389.5);

    companion object {
        fun heaviest(): Planet = values().maxByOrNull { it.mass } ?: EARTH
    }
}

fun main() {
    println(Planet.heaviest())
}

A Compilation error: companion object syntax

B MARS

C EARTH

D Runtime exception: null pointer

💡 Hint

Check which planet has the greater mass.

EARTH has a larger mass than MARS, so heaviest() returns EARTH.

🧠 Conceptual

expert

Number of enum constants with overridden methods

Given this Kotlin enum, how many constants override the abstract method `sound()`?

Kotlin

enum class Animal {
    DOG {
        override fun sound() = "Bark"
    },
    CAT {
        override fun sound() = "Meow"
    },
    COW {
        override fun sound() = "Moo"
    },
    FISH;

    abstract fun sound(): String
}

A 0

B 3

C 1

D 4

💡 Hint

Check which constants provide a method body for sound().

DOG, CAT, and COW override sound(). FISH does not and will cause a compilation error if used.