Enum with properties and methods in Kotlin - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to declare an enum class named Color.

Kotlin

enum class [1] {
    RED, GREEN, BLUE
}

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

Acolor

BPaint

CColors

DColor

Attempts:

3 left

💡 Hint

Common Mistakes

Using lowercase names for enum classes.

Using plural form when singular is expected.

The enum class must be named Color exactly as specified.

2fill in blank

medium

Complete the code to add a property 'rgb' to each enum constant.

Kotlin

enum class Color(val [1]: Int) {
    RED(0xFF0000), GREEN(0x00FF00), BLUE(0x0000FF)
}

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

Avalue

Brgb

Ccode

DcolorCode

Attempts:

3 left

💡 Hint

Common Mistakes

Using generic names like 'code' or 'value' instead of 'rgb'.

Using camelCase incorrectly.

The property name is rgb to represent the color code.

3fill in blank

hard

Fix the error in the method that returns the color name in lowercase.

Kotlin

enum class Color(val rgb: Int) {
    RED(0xFF0000), GREEN(0x00FF00), BLUE(0x0000FF);

    fun colorName() = name.[1]()
}

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Alowercase

BtoLowerCase

CtoUpperCase

Duppercase

Attempts:

3 left

💡 Hint

Common Mistakes

Using Java method toLowerCase() which is deprecated in Kotlin.

Using uppercase methods instead of lowercase.

In Kotlin, the correct method to convert a string to lowercase is lowercase().

4fill in blank

hard

Fill both blanks to add a method that returns the hex string of the rgb value.

Kotlin

enum class Color(val rgb: Int) {
    RED(0xFF0000), GREEN(0x00FF00), BLUE(0x0000FF);

    fun hex() = "#$[1].format(\"%06X\", [2] )"
}

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AString

Brgb

CInt

Dthis.rgb

Attempts:

3 left

💡 Hint

Common Mistakes

Using Int.format which does not exist.

Using this.rgb instead of just rgb.

The String.format method is used to format the rgb integer as a hex string.

So String.format and rgb are needed.

5fill in blank

hard

Fill all three blanks to create a companion object with a method that finds a Color by its rgb value.

Kotlin

enum class Color(val rgb: Int) {
    RED(0xFF0000), GREEN(0x00FF00), BLUE(0x0000FF);

    companion object {
        fun fromRgb(value: Int): Color? = values().[1] { it.[2] == [3] }
    }
}

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

Afind

Brgb

Cvalue

DfirstOrNull

Attempts:

3 left

💡 Hint

Common Mistakes

Using find which is not a Kotlin standard function.

Mixing up parameter names inside the lambda.

The method firstOrNull finds the first enum constant matching the condition or returns null.

The lambda compares it.rgb with the input value.

Practice

1. What is the main purpose of using an enum with properties and methods in Kotlin?

easy

A. To group related fixed values with additional data and behavior

B. To create a list of unrelated variables

C. To define functions without any fixed values

D. To replace all classes in Kotlin

Solution

1. Step 1: Understand enum basics

   Enums group fixed related values, like days or colors.

2. Step 2: Recognize added properties and methods

   Adding properties and methods lets each enum value hold extra data and behavior.

3. Final Answer:

   To group related fixed values with additional data and behavior -> Option A

4. Quick Check:

   Enums = fixed values + extra data [OK]

Hint: Enums bundle fixed options with data and actions [OK]

Common Mistakes:

• Thinking enums are for unrelated variables
• Confusing enums with regular classes
• Assuming enums can't have methods

2. Which of the following is the correct syntax to declare an enum with a property color of type String in Kotlin?

easy

A. enum class Fruit { APPLE(color = "Red"), BANANA(color = "Yellow") }

B. enum Fruit { APPLE: String = "Red", BANANA: String = "Yellow" }

C. enum class Fruit(val color: String) { APPLE("Red"), BANANA("Yellow") }

D. enum class Fruit { val color: String = "Red"; APPLE, BANANA }

Solution

1. Step 1: Check enum class declaration with property

   In Kotlin, enum classes can have constructor parameters like val color: String.

2. Step 2: Verify enum values initialization

   Each enum value must pass the property value in parentheses, e.g., APPLE("Red").

3. Final Answer:

   enum class Fruit(val color: String) { APPLE("Red"), BANANA("Yellow") } -> Option C

4. Quick Check:

   Enum with constructor and values = enum class Fruit(val color: String) { APPLE("Red"), BANANA("Yellow") } [OK]

Hint: Use constructor parameters and pass values in parentheses [OK]

Common Mistakes:

• Using colon syntax instead of constructor parameters
• Trying to assign properties inside enum body incorrectly
• Omitting parentheses for enum values

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

enum class Size(val label: String) {
    SMALL("S"), MEDIUM("M"), LARGE("L");
    fun description() = "Size is $label"
}

fun main() {
    println(Size.MEDIUM.description())
}

medium

A. Size is M

B. Size is MEDIUM

C. MEDIUM

D. Size.MEDIUM

Solution

1. Step 1: Understand enum property and method

   Each enum value has a label property: MEDIUM has "M".

2. Step 2: Evaluate the description() method call

   The method returns "Size is $label", so for MEDIUM it returns "Size is M".

3. Final Answer:

   Size is M -> Option A

4. Quick Check:

   Method uses label property = "Size is M" [OK]

Hint: Method uses property value, not enum name [OK]

Common Mistakes:

• Printing enum name instead of property
• Confusing property label with enum constant name
• Ignoring method call output

4. Identify the error in this Kotlin enum declaration:

enum class Direction(val degrees: Int) {
    NORTH(0),
    EAST(90),
    SOUTH(180),
    WEST
}

medium

A. Semicolon missing after enum constants

B. Cannot have properties in enum classes

C. Enum constants must be lowercase

D. Missing property value for WEST enum constant

Solution

1. Step 1: Check enum constructor parameters

   The enum class requires an Int parameter degrees for each constant.

2. Step 2: Verify each enum constant initialization

   All constants except WEST provide a value; WEST is missing (value).

3. Final Answer:

   Missing property value for WEST enum constant -> Option D

4. Quick Check:

   All enum constants must pass constructor values [OK]

Hint: All enum constants must provide constructor arguments [OK]

Common Mistakes:

• Forgetting to pass constructor arguments for all constants
• Assuming semicolon is mandatory after constants
• Thinking enum constants must be lowercase

5. Given this enum with a method:

enum class TrafficLight(val duration: Int) {
    RED(30) {
        override fun signal() = "Stop"
    },
    YELLOW(5) {
        override fun signal() = "Caution"
    },
    GREEN(25) {
        override fun signal() = "Go"
    };
    abstract fun signal(): String
}

fun main() {
    val lights = TrafficLight.values()
    val signals = lights.map { it.signal() }
    println(signals)
}

What is the output when running main()?

hard

A. [30, 5, 25]

B. ["Stop", "Caution", "Go"]

C. [RED, YELLOW, GREEN]

D. ["Go", "Caution", "Stop"]

Solution

1. Step 1: Understand enum with abstract method

   Each enum constant overrides signal() to return a specific string.

2. Step 2: Map enum values to their signals

   The map calls signal() on each constant, producing ["Stop", "Caution", "Go"].

3. Final Answer:

   ["Stop", "Caution", "Go"] -> Option B

4. Quick Check:

   Abstract method overridden per constant = correct signals [OK]

Hint: Abstract method overridden per enum constant returns correct string [OK]

Common Mistakes:

• Printing enum names instead of method results
• Confusing property values with method outputs
• Ignoring abstract method override requirement