Re: Subclassing EnumSet to add an interface?

"Mike Schilling" <>
Sat, 12 May 2007 00:11:28 -0700
"Eric Smith" <> wrote in message

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.

I tried:

 import java.util.EnumSet;

 public abstract class Foo<E extends Enum<E>> extends EnumSet<E>
                                              implements Comparable<Foo>
   public int compareTo (Foo o)
     return 1; // dummy value for now

The compiler says: cannot find symbol
 symbol : constructor EnumSet()
 location: class java.util.EnumSet<E>
 public abstract class Foo<E extends Enum<E>> extends EnumSet<E>
 1 error

You're not specifying a constructor, so one is being created for you, which
looks like

    public Foo()

The compiler is complaining that the constructor "super()" is attempting to
call doesn't exist. In fact, since EnumSet has no public constructors, it
cannot be subclassed (other than, perhaps, within its package.)

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