Is it possible to extend Java Enums?

Question

Here's what I am looking to accomplish, I have a class that has an enum of some values and I want to subclass that and add more values to the enum. This is a bad example, but:

public class Digits {  public enum Digit  {   0, 1, 2, 3, 4, 5, 6, 7, 8, 9  } }  public class HexDigits extends Digits {  public enum Digit  {   A, B, C, D, E, F  } } 

so that HexDigits.Digit contains all Hex Digits. Is that possible?

Answer 1

No it's not possible. The best you can do is make two enums implement and interface and then use that interface instead of the enum. So:

interface Digit {   int getValue(); }  enum Decimal implements Digit {   ZERO, ONE, TWO, THREE, FOUR, FIVE, SIX, SEVEN, EIGHT, NINE;    private final int value;    Decimal() {     value = ordinal();   }    @Override   public int getValue() {     return value;   } }  enum Hex implements Digit {   A, B, C, D, E, F;    private final int value;    Hex() {     value = 10 + ordinal();   }    @Override   public int getValue() {     return value;   } } 

Answer 2

No.

Enums cannot be subclassed.

The reasoning here is that an enumeration defines a fixed number of values. Subclassing would break this.