enum class
- Kotlin course
- Beginner
- Lesson 94/116
- 4 min
Learn to define named constants with enum class.
enum class: named constants
An enum class defines a fixed set of values. Each constant has a name; a typo is caught at compile time. It is ideal for colors, directions, days of the week.
enum class Color { RED, GREEN, BLUE }
val c = Color.RED
println(c) // REDConstants are separated by commas inside braces. To access one, write Color.RED. You use a meaningful name instead of a number, which improves readability.
Accessing an enum constant
To access a constant, write ClassName.CONSTANT. A constant is an object; the name property returns its name.
val r = Color.RED
println(r.name) // "RED"
println(r) // REDComparing two constants with == is safe; each constant is a single object. name always returns the name as declared. This gives you consistent output in logs or interfaces.
Practice Define the Signal enum
Define an enum class called Signal with RED, YELLOW, GREEN. In main print the Signal.YELLOW constant with println.
Starter code
fun main() {
// Define a signal type and print one constant
}Sample solution
enum class Signal { RED, YELLOW, GREEN }
fun main() {
println(Signal.YELLOW)
}Expected output
YELLOW
Questions and answers
Review the lesson questions together with their answers. To test yourself, solve the lesson interactively.
1 What kind of values does an enum class hold?
- Random numbers
- Named constants Correct answer
- Dynamic text
- File paths
Explanation: Each constant has a name; the compiler checks them.
2 Fill in the blank: enum constant
val c = Color.____val c = Color.REDExplanation: Color.RED accesses the constant.
3 Match constant to meaning
| Term | Meaning |
|---|---|
RED |
Red |
GREEN |
Green |
BLUE |
Blue |
name |
Constant name |