Kotlin Enum

Enum classes as any other classes can have a constructor and be initialized

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

Functions and Properties in enums

Enum classes can also declare members (i.e. properties and functions). A semicolon (;) must be placed between the last enum object and the first member declaration. If a member is abstract, the enum objects must implement it.

enum class Color {
 RED {
 override val rgb: Int = 0xFF0000
 },
 GREEN {
 override val rgb: Int = 0x00FF00
 },
 BLUE {
 override val rgb: Int = 0x0000FF
 }
 ;
 abstract val rgb: Int
 fun colorString() = "#%06X".format(0xFFFFFF and rgb)
}

Simple enum

Each enum constant is an object. Enum constants are separated with commas.

enum class Color {
 RED, GREEN, BLUE
}

Mutability

Enums can be mutable, this is another way to obtain a singleton behavior:

enum class Planet(var population: Int = 0) {
 EARTH(7 * 100000000),
 MARS();
 override fun toString() = "$name[population=$population]"
}

 println(Planet.MARS) // MARS[population=0]
 Planet.MARS.population = 3
 println(Planet.MARS) // MARS[population=3]