Summary - Enums

Combine enum class and when to write a state machine.

Summary - Enums

In this group you learned to declare an enum class, access constants with entries/valueOf/ordinal, add properties and methods, write exhaustive branches with when and loop over entries.

Now it is time to combine them in a small task: define an enum, print its count and its first constant. This is a small sample of a real choice structure.

Exercise Count days and print the first

Define an enum class called Day with MON, TUE, WED, THU, FRI. In main first print Day.entries.size, then Day.entries.first().

Show example solution

enum class Day { MON, TUE, WED, THU, FRI }

fun main() {
    println(Day.entries.size)
    println(Day.entries.first())
}

Test yourself

Fill in the blank: get the order

val s = Color.GREEN.____

Show answer

val s = Color.GREEN.ordinal

Match tool to purpose

enum class

Declaration
entries

All constants
when

All branches
ordinal

Order
Which is true about enum constants?
- Enum constants are mutable
- Enums only hold numbers
- Enum constants are fixed
- Enums cannot implement interfaces
Show answer

Enum constants are fixed — Each constant is a single object; it does not change after compile.

Next lesson: try/catch

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