Enumerating Enum class from type parameter

Question

Hi I'm trying to provide an enum to a generic class so I can iterate over the a set of members defined by the supplied Enum type parameter. I found a way to do this, but in order for it to work, I need to supply an arbitrary instance of the enum.

public enum suits {
        spades,
        hearts,
        diamonds,
        clubs;
}

public static class Card<E extends Enum<E>> {
  public final EnumSet<E> suits;

  public Card(E instance) {
     EnumSet<E> mySet = EnumSet.allOf(instance.getDeclaringClass());
     this.suits = mySet;
  }
}

Now I can do something like this:

Card<Suits> myCard = new Card<Suits>(Suits.clubs);
String names = "";
for (Suit s : myCard.suits) {names += s.name + "|";} // "spades|hears|diamonds|clubs|

Here is the question: Can I do this without supplying an instance of the enum in the Card object constructor?

What I would think ought to work is to replace instance.getDeclaringClass() with the type parameter when creating the enum, as in:

EnumSet<E> mySet = EnumSet.allOf(E);

but that gives a syntax error. Somehow it seems like it should be possible to get type type parameter without having to resort to supplying an enum instance and then calling getDeclaringClass().

Louis Wasserman · Accepted Answer · 2014-10-20 00:30:11Z

1

You can pass in Suits.class, but you need one or the other -- either an instance of the enum type, or a Class object for the enum type.

answered Oct 20, 2014 at 0:30

Louis Wasserman

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2 Comments

GGizmos Over a year ago

So there is no way to either derive an instance or a Class object from a type parameter that is scoped to an enum type.

Louis Wasserman Over a year ago

Nope. Generics don't exist at runtime.

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