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

The Comparable example given by several people here is wrong, since Enum already implements that. You can't even override it.

A better example is having an interface that defines, let's say, a data type. You can have an enum to implement the simple types, and have normal classes to implement complicated types:

interface DataType {
  // methods here
}

enum SimpleDataType implements DataType {
  INTEGER, STRING;

  // implement methods
}

class IdentifierDataType implements DataType {
  // implement interface and maybe add more specific methods
}