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Enum properties

Learn to define properties and methods in enums.

Enum properties: constructor and field

An enum class can take a constructor and properties. Each constant is declared with a value that fits the constructor.

enum class Planet(val distance: Int) {
    MERCURY(57), VENUS(108), EARTH(150)
}
println(Planet.EARTH.distance)  // 150

Each constant takes a value in parentheses; the value binds to the distance property. This lets you attach meaningful data to constants. Data lives with the constant; no separate table is needed.

Methods inside an enum

You can define a method inside an enum class. The method can access the constant's properties.

enum class Planet(val distance: Int) {
    MERCURY(57), VENUS(108), EARTH(150);
    fun isClose() = distance < 100
}
println(Planet.EARTH.isClose())  // false

A semicolon goes after the constant list; then the method follows. Inside the method you access properties like distance directly. This way behaviour lives with the data.

Practice Add an emoji property to Mood

Define an enum class called Mood with a constructor property val emoji: String. Constants: HAPPY(":)"), SAD(":("). In main print the emoji value of the HAPPY constant.

Starter code

Main.kt
fun main() {
    // Define a mood type and print one constant's emoji
}

Sample solution

Main.kt
enum class Mood(val emoji: String) {
    HAPPY(":)"), SAD(":(")
}

fun main() {
    println(Mood.HAPPY.emoji)
}

Expected output

:)

Questions and answers

Review the lesson questions together with their answers. To test yourself, solve the lesson interactively.

1 Fill in the blank: declare the property

Question 
enum class Planet(val ____: Int) { MERCURY(57), VENUS(108) }
Answer 
enum class Planet(val distance: Int) { MERCURY(57), VENUS(108) }

Explanation: val distance: Int comes with the constructor.

2 What does enum class Planet(val distance: Int) define?

  • An interface
  • Only a method
  • Only constants
  • A property and constructor Correct answer

Explanation: The distance property comes from the constructor parameter.

3 Match piece to role

Term Meaning
distance Planet property
MERCURY(57) Constructor call
isClose() Method
57 Value

4 Fill in the blank: call the method

Question 
val p = Planet.EARTH
val close = p.____()
Answer 
val p = Planet.EARTH
val close = p.isClose()

Explanation: you call the isClose() method.

All lessons in Beginner

1 Kotlin basics

  1. What is Kotlin?
  2. Your first program
  3. The main function
  4. Comments
  5. String templates
  6. Summary - Kotlin basics

2 Variables

  1. val and var
  2. Type inference
  3. const
  4. lateinit
  5. by lazy
  6. Summary - Variables

3 Data types

  1. Integer types
  2. Floating-point types
  3. Boolean and Char
  4. String
  5. Any and Unit
  6. Summary - Data types

4 Project: Calculator

  1. Project design
  2. Add and subtract
  3. Multiply and divide
  4. Error handling
  5. Putting it together

5 Operators

  1. Arithmetic operators
  2. Assignment operators
  3. Comparison operators
  4. Logical operators
  5. Elvis operator
  6. Summary - Operators

6 Strings

  1. Creating strings
  2. String templates
  3. String methods
  4. substring
  5. split and replace
  6. Summary - Strings

7 Conditionals

  1. The if statement
  2. else and else if
  3. if expression
  4. when
  5. when expression
  6. Summary - Conditionals

8 Loops

  1. The for loop
  2. The while loop
  3. The do-while loop
  4. Range
  5. break and continue
  6. Summary - Loops

9 Project: Shopping cart

  1. Cart design
  2. Adding items
  3. Calculating totals
  4. Listing the cart
  5. Putting it together

10 Arrays

  1. Creating arrays
  2. Array access
  3. Array size
  4. Array loop
  5. Array methods
  6. Summary - Arrays

11 Lists

  1. Creating lists
  2. List operations
  3. List access
  4. List iteration
  5. List methods
  6. Summary - Lists

12 Maps and Sets

  1. Creating sets
  2. Set operations
  3. Creating maps
  4. Map operations
  5. Map iteration
  6. Summary - Maps and Sets

13 Functions

  1. Defining functions
  2. Return values
  3. Expression body
  4. Default parameters
  5. Named arguments
  6. Summary - Functions

14 Null safety

  1. Nullable types
  2. ?, !! and ?:
  3. let
  4. Null check
  5. lateinit
  6. Summary - Null safety

15 Project: To-do CLI

  1. Task model
  2. Adding tasks
  3. Listing tasks
  4. Completing tasks
  5. Putting it together

16 Advanced string operations

  1. Regex
  2. matches and find
  3. replace
  4. StringBuilder
  5. trim and pad
  6. Summary - Advanced strings

17 Enums

  1. enum class
  2. Enum values
  3. Enum properties
  4. when with enum
  5. Enum and range
  6. Summary - Enums

18 Exceptions

  1. try/catch
  2. throw
  3. finally
  4. try expression
  5. Custom exceptions
  6. Summary - Exceptions

19 Class basics

  1. class
  2. Constructor
  3. Properties
  4. Methods
  5. this
  6. Summary - Class basics

20 Beginner final

  1. Project design
  2. Classes
  3. Collections
  4. Error handling
  5. Putting it together