Re: Generics and Enums

From:

Patricia Shanahan <pats@acm.org>

Newsgroups:

comp.lang.java.help

Date:

Mon, 30 Jul 2007 00:28:37 GMT

Message-ID:

<Vgari.12230$tj6.4871@newsread4.news.pas.earthlink.net>

amberarrow@gmail.com wrote:

On Jul 29, 1:54 pm, Lew <l...@lewscanon.nospam> wrote:

Roedy Green wrote:

On Sun, 29 Jul 2007 10:55:27 -0700, "amberar...@gmail.com"
<amberar...@gmail.com> wrote, quoted or indirectly quoted someone who
said :

I'm trying to write a generic class that takes an Enum as generic
parameter but
I'm not able to compile it:
------------------------------------
public class Foo<T extends Enum> {

Your class is similar to an EnumSet in terms of its Generics. So I
had a peek at how EnumSet does this
public abstract class EnumSet<E extends Enum<E>> extends
AbstractSet<E>
implements Cloneable, java.io.Serializable

This would allow the OP to eliminate the illegal "T.values()" expression and
just call "values()".

--
Lew

I changed "Foo<T extends Enum>" to "Foo<T extends Enum<T>>" but get
the same error.
I also changed T.values() to just values() but that results in a
compile error
saying it cannot find the method values().

I think you need to copy one more thing from EnumSet. Each of its
methods gets as parameter an element of the enum, or the Enum's Class
object, or an existing collection based on the Enum.

For example, noneOf requires the Class object.

In effect, it always has access to the Class object, either directly or
by asking an element for its getClass(). As it happens, Class has a
method getEnumConstants().

Patricia