Re: limitations on using enum as generic parameter

From:

Daniele Futtorovic <da.futt.news@laposte.net.invalid>

Newsgroups:

comp.lang.java.programmer

Date:

Tue, 08 Feb 2011 19:35:39 +0100

Message-ID:

<iis2dp$qbs$1@news.eternal-september.org>

On 08/02/2011 18:50, dalamb@cs.queensu.ca allegedly wrote:

I am playing around with using enums and generics together in Java 1.5
(yes, I know it's in end-of-life, but it would be a bit of trouble
right now to go to 1.6 let alone 1.7). Having figured out some simple
situations, I tried writing a generic class that takes an enum as a
type parameter. Unfortunately I don't seem to be able to invoke the
enum's values() method -- javac says "Cannot find symbol: method
values()". (the reference to Enum.valueof later also gets errors,
which is why I commented it out to simplify the test).

Is there any way around this, or is there just no way to refer to an
enum's values() method when the enum is a generic parameter?

Here's the code; interface MessageCode should be irrelevant because it
could be any old interface for the purposes of this example:

public class EnumCodeSet<E extends Enum& MessageCode>
                // implements MessageCodeSet
{
     private E[] enums;
     public EnumCodeSet() {
    enums = E.values();
     }

     public MessageCode get(int index)
    throws IndexOutOfBoundsException
     {
    return enums[index];
     } // get

     public MessageCode valueOf(String name)
    throws IllegalArgumentException, NullPointerException
     {
    // return Enum.valueof(E,name);
     } //
} // end class EnumCodeSet

HTH.

public class EnumCodeSet<E extends Enum<E> & MessageCode>
{
     private final Class<E> clazz;
     public EnumCodeSet( Class<E> clazz ) {
         if( clazz == null ) {
             throw new IllegalArgumentException( new
NullPointerException() );
         }

         this.clazz = clazz;
     }

     public MessageCode get(int index)
    throws IndexOutOfBoundsException
     {
         return clazz.getEnumConstants()[ index ];
     } // get

     public MessageCode valueOf(String name)
    throws IllegalArgumentException, NullPointerException
     {
         return Enum.valueOf(clazz, name);
     } //
} // end class EnumCodeSet