How can I create "static" method for enum in Kotlin?

Question

Kotlin already have number of "static" methods for enum class, like values and valueOf

For example I have enum

public enum class CircleType {
    FIRST
    SECOND
    THIRD
}

How can I add static method such as random(): CircleType? Extension functions seems not for this case.

Solution

Just like with any other class, you can define a class object in an enum class:

enum class CircleType {
  FIRST,
  SECOND,
  THIRD;
  companion object {
     fun random(): CircleType = FIRST // http://dilbert.com/strip/2001-10-25
  }
}

Then you'll be able to call this function as CircleType.random().

EDIT: Note the commas between the enum constant entries, and the closing semicolon before the companion object. Both are now mandatory.

Comments

[Ilya Ryzhenkov]

If you want it to be visible from Java as a static method, you need to annotate it with [platformStatic] as well.

[Raphael]

@JasperBlues Does for me, on Kotlin 1.1.1.

[Kishan B]

Now you need to use @JvmStatic kotlinlang.org/docs/reference/…

[HendraWD]

Use @JvmStatic if only you really want to use with Java, otherwise it's just waste of resources

[jiahao]

This is great. Just one more note: In order to access the static method, you need to add the keyword "Companion" between the class and the method, otherwise it won't work. Here is an example: jiahaoliuliu.com/2018/04/kotlin-static-method-at-enum.html

[yole]

The Companion reference is only needed if you're accessing the method from Java code, not from Kotlin.

[Farid]

@yole to your last comment; IDE complains when used without companion reference even if it's Kotlin (version 1.3.50)

[Leonardo Sibela]

I was trying to use a companion object, but the problem was that I forgot about the ; after declaring all the values from my enum. I think that using kotling made me pick up some bad habits lol

[Siamak]

@HendraWD Using @JvmStatic has almost no effect on resource.

[HendraWD]

@Siamak SiaSoft @JvmStatic has effect. When you decompile the bytecode, you will see more codes added because of @JvmStatic

[Siamak]

@HendraWD I see but adding few lines of code for the sake of code simplicity and compatibility does not mean it's resource consuming. Indeed it's not free though :)

[HendraWD]

@SiamakSiaSoft yes I agree, that's why I wrote: Use @JvmStatic if only you really want to use with Java