Path: csiph.com!v102.xanadu-bbs.net!xanadu-bbs.net!feeder.erje.net!eu.feeder.erje.net!eternal-september.org!feeder.eternal-september.org!news.eternal-september.org!.POSTED!not-for-mail
From: Eric Sosman <esosman@comcast-dot-net.invalid>
Newsgroups: comp.lang.java.programmer
Subject: Re: Accessibility of suBclass-fields from suPERclass (reflection)
Date: Sun, 17 Aug 2014 15:24:51 -0400
Organization: A noiseless patient Spider
Lines: 44
Message-ID: <lsqvi4$t4i$1@dont-email.me>
References: <slrnluqmpu.fp3.avl@login.logic.tuwien.ac.at> <53eecf6a$0$300$14726298@news.sunsite.dk> <slrnluu6ir.fp3.avl@login.logic.tuwien.ac.at> <c58q1fF9v1tU1@mid.individual.net> <slrnluvn8q.fp3.avl@login.logic.tuwien.ac.at> <lsosjs$gtc$1@dont-email.me> <slrnlv1rkm.fp3.avl@login.logic.tuwien.ac.at>
Mime-Version: 1.0
Content-Type: text/plain; charset=windows-1252; format=flowed
Content-Transfer-Encoding: 7bit
Injection-Date: Sun, 17 Aug 2014 19:24:52 +0000 (UTC)
Injection-Info: mx05.eternal-september.org; posting-host="bd4e1cba8d8592bec5d5ed9e4537fbfd"; logging-data="29842"; mail-complaints-to="abuse@eternal-september.org";	posting-account="U2FsdGVkX1/8lbvGEeC0tiXO30qwGC2+"
User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:31.0) Gecko/20100101 Thunderbird/31.0
In-Reply-To: <slrnlv1rkm.fp3.avl@login.logic.tuwien.ac.at>
Cancel-Lock: sha1:4xGSIUmycA+Q9GH02XVdkQHs9Gw=
Xref: csiph.com comp.lang.java.programmer:29710

On 8/17/2014 2:04 PM, Andreas Leitgeb wrote:
> Eric Sosman <esosman@comcast-dot-net.invalid> wrote:
>> On 8/16/2014 6:37 PM, Andreas Leitgeb wrote:
>>> I have a special Base class, and each of its subclasses serve exactly
>>> one purpose: a collection of name/value associations where the java-
>>> compiler knows about the valid names, so as to detect accesses to
>>> non-existing names already at compile-time.  (without that last premise,
>>> I would have used HashMaps instead of subclasses)
>>       Would an EnumMap serve?
>
> In principle yes, but...
>
> ... element-access would look like:
>
>       someSpecificEnumMapInstance.get( SomeSpecificEnum.itemName )
>
> instead of:
>
>       someSpecificSubClassInstance.itemName

     We can all bemoan Java's occasional wordiness, but wasn't your
original code something like

	Value value;
	try {
	    Field f = someSpecificSubClassInstance
	       .getClass().getField("itenName");
	    f.setAccessible(true);  // if needed
	    value = (Value) f.get(someSpecificSubClassInstance);
	} catch (NoSuchFieldException | SecurityException | ... ex) {
	    throw SelfInflictedWoundException(ex);
	}

?  This is way wordier than using an EnumMap, *and* it prevents rather
than enables compile-time checking -- did you spot the typo?

     I'm confident that you've got a credible use case, but I'm less
confident that you've got a credible use case for this technique.  If
you'd reveal a little more about the larger problem, perhaps someone
could suggest an alternative approach -- that might even turn out to
be a better choice all around.

-- 
esosman@comcast-dot-net.invalid