Why would an Enum implement an Interface?

Question

I just found out that Java allows enums to implement an interface. What would be a good use case for that?

Answer 1

Enums don't just have to represent passive sets (e.g. colours). They can represent more complex objects with functionality, and so you're then likely to want to add further functionality to these - e.g. you may have interfaces such as Printable, Reportable etc. and components that support these.

Answer 2

Most common usage for this would be to merge the values of two enums into one group and treat them similarly. For example, see how to join Fruits and Vegatables.

Answer 3

Enums are like Java Classes, they can have Constructors, Methods, etc. The only thing that you can't do with them is new EnumName(). The instances are predefined in your enum declaration.

Answer 4

Here's my reason why ...

I have populated a JavaFX ComboBox with the values of an Enum. I have an interface, Identifiable (specifying one method: identify), that allows me to specify how any object identifies itself to my application for searching purposes. This interface enables me to scan lists of any type of objects (whichever field the object may use for identity) for an identity match.

I'd like to find a match for an identity value in my ComboBox list. In order to use this capability on my ComboBox containing the Enum values, I must be able to implement the Identifiable interface in my Enum (which, as it happens, is trivial to implement in the case of an Enum).