Re: Subclassing EnumSet to add an interface?

Lasse Reichstein Nielsen <>
Sat, 12 May 2007 15:26:17 +0200
Eric Smith <> writes:

I'd like to create a subclass of EnumSet to implement the Comparable
interface (using my own arbitrary ordering, so that I can use the
subclass as a key in a dictionary), but I can't seem to figure
out how to do it.

As others have pointed out, EnumSet cannot be subclassed.

Two approaches spring to mind, if all you need are keys based on
sets of enum values:

Make an adapter key object containing the EnumSet:

  class MyDictionaryKey<T extends Enum>
    implements Comparable<MyDictionaryKey<T>> {
      private final EnumSet<T> enumSet;
      public MyDictionaryKey(EnumSet<T> enumSet) {
        this.enumSet = enumSet;
      public EnumSet<T> getEnumSet() {
        return enumSet;
      public int compareTo(MyDictionaryKey<T> other) {
        /// ...your impl

and use it for keys in your dictionary.

Or, create a Comparator<EnumSet<MyEnum>> and use a dictionary
that allows a comparator for the keys.

Lasse Reichstein Nielsen -
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