Groups > comp.lang.java.programmer > #7210

Re: Using Enumerated Types as Array Indexes

From	Arved Sandstrom <asandstrom3minus1@eastlink.ca>
Newsgroups	comp.lang.java.programmer
Subject	Re: Using Enumerated Types as Array Indexes
References	(4 earlier) <j2fc1g$b9j$1@dont-email.me> <6d418cda-dab3-43df-a9ec-293b43f2bbd8@glegroupsg2000goo.googlegroups.com> <vTL2q.38278$tp.27319@newsfe06.iad> <slrnj4ngfi.6gl.avl@gamma.logic.tuwien.ac.at> <f08d98e8-e04d-4d4e-b518-44bba735dba6@glegroupsg2000goo.googlegroups.com>
Message-ID	<rY43q.61720$7K4.15412@newsfe14.iad> (permalink)
Organization	Public Usenet Newsgroup Access
Date	2011-08-18 06:29 -0300

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On 11-08-17 11:17 AM, Lew wrote:
> Andreas Leitgeb wrote:
>> Arved Sandstrom <asandstr...@eastlink.ca> wrote:
>>> Lew wrote:
>>>> JLS 10: [...]
>>>> IOW, you never index arrays with a byte, char or short. [...]
>>> I'm feeling slow this morning: how do we get problems with byte->int,
>>> short->int, or char->int again?
> 
> One gets problems with byte->int and short->int with array indexes the way one gets into trouble with those widening conversions generally.  The usual suspect is the lack of unsigned versions, so widening a (byte)0xA0, for example, would result in a negative index.
> 
> One gets into trouble generally in programming when one thinks one thing is going on ("index takes a byte") whilst ignoring what's really going on (there's a widening conversion involved).  You might get away with it most of the time, but occasionally such things trip you up.  
> 
> Why think about it imprecisely?  Tell us the advantage of that, please.
> 
>> array-indexing takes integers.  That you can also throw byte/short/char
>> values at them without cast doesn't mean that arrays "take" those, but
>> only that such values get automatically converted to int before being
>> taken by the array for indexing.
>>
>> An example for something really "taking" byte-values:
>>   foo(byte b) { ... }
> 
I'll try my answer again, it seems not to have hit the airwaves.

I don't see my imprecision: the JLS very clearly says that integral
widening primitive conversions result in *no* loss of information; this
is just common sense when you consider what's going on with char->int,
byte-int and short->int.

I reiterate: the _JLS_ says that there is *no* loss of information. I
don't see why you believe the JLS is wrong. Exactly how are you getting
into trouble with integral widening primitive conversions?

Furthermore, your assertion about indexing into an array with (byte)0x0A
(or any other legal byte value for that matter) is just plain incorrect,
and can be disproved in a minute or two. Indexing into any array with
(byte)0x0A returns the 11th element of a (sufficiently large) array.

AHS

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Using Enumerated Types as Array Indexes KevinSimonson <kvnsmnsn@hotmail.com> - 2011-08-16 07:53 -0700
  Re: Using Enumerated Types as Array Indexes Patricia Shanahan <pats@acm.org> - 2011-08-16 09:30 -0700
  Re: Using Enumerated Types as Array Indexes Tom Anderson <twic@urchin.earth.li> - 2011-08-16 21:37 +0100
  Re: Using Enumerated Types as Array Indexes Gene Wirchenko <genew@ocis.net> - 2011-08-16 14:54 -0700
    Re: Using Enumerated Types as Array Indexes Arne Vajhøj <arne@vajhoej.dk> - 2011-08-16 20:47 -0400
  Re: Using Enumerated Types as Array Indexes Arne Vajhøj <arne@vajhoej.dk> - 2011-08-16 20:38 -0400
    Re: Using Enumerated Types as Array Indexes markspace <-@.> - 2011-08-16 17:52 -0700
      Re: Using Enumerated Types as Array Indexes Arne Vajhøj <arne@vajhoej.dk> - 2011-08-16 21:56 -0400
        Re: Using Enumerated Types as Array Indexes markspace <-@.> - 2011-08-16 20:20 -0700
          Re: Using Enumerated Types as Array Indexes Lew <lewbloch@gmail.com> - 2011-08-16 20:45 -0700
            Re: Using Enumerated Types as Array Indexes Arved Sandstrom <asandstrom3minus1@eastlink.ca> - 2011-08-17 06:31 -0300
              Re: Using Enumerated Types as Array Indexes Andreas Leitgeb <avl@gamma.logic.tuwien.ac.at> - 2011-08-17 13:28 +0000
                Re: Using Enumerated Types as Array Indexes Lew <lewbloch@gmail.com> - 2011-08-17 07:17 -0700
                Re: Using Enumerated Types as Array Indexes Robert Klemme <shortcutter@googlemail.com> - 2011-08-17 19:02 +0200
                Re: Using Enumerated Types as Array Indexes markspace <-@.> - 2011-08-17 16:09 -0700
                Re: Using Enumerated Types as Array Indexes Andreas Leitgeb <avl@gamma.logic.tuwien.ac.at> - 2011-08-17 23:48 +0000
                Re: Using Enumerated Types as Array Indexes markspace <-@.> - 2011-08-17 17:34 -0700
                Re: Using Enumerated Types as Array Indexes Patricia Shanahan <pats@acm.org> - 2011-08-17 18:07 -0700
                Re: Using Enumerated Types as Array Indexes markspace <-@.> - 2011-08-18 08:22 -0700
                Re: Using Enumerated Types as Array Indexes Andreas Leitgeb <avl@gamma.logic.tuwien.ac.at> - 2011-08-18 18:37 +0000
                Re: Using Enumerated Types as Array Indexes markspace <-@.> - 2011-08-18 11:50 -0700
                Re: Using Enumerated Types as Array Indexes Andreas Leitgeb <avl@gamma.logic.tuwien.ac.at> - 2011-08-18 20:49 +0000
                Re: Using Enumerated Types as Array Indexes markspace <-@.> - 2011-08-18 14:48 -0700
                Re: Using Enumerated Types as Array Indexes Andreas Leitgeb <avl@gamma.logic.tuwien.ac.at> - 2011-08-18 22:50 +0000
                Re: Using Enumerated Types as Array Indexes Arne Vajhøj <arne@vajhoej.dk> - 2011-08-17 21:49 -0400
                Re: Using Enumerated Types as Array Indexes Eric Sosman <esosman@ieee-dot-org.invalid> - 2011-08-17 21:50 -0400
                Re: Using Enumerated Types as Array Indexes Robert Klemme <shortcutter@googlemail.com> - 2011-08-19 14:13 +0200
                Re: Using Enumerated Types as Array Indexes Andreas Leitgeb <avl@gamma.logic.tuwien.ac.at> - 2011-08-19 20:05 +0000
                Re: Using Enumerated Types as Array Indexes Robert Klemme <shortcutter@googlemail.com> - 2011-08-20 00:20 +0200
                Re: Using Enumerated Types as Array Indexes Andreas Leitgeb <avl@gamma.logic.tuwien.ac.at> - 2011-08-19 23:11 +0000
                Re: Using Enumerated Types as Array Indexes Robert Klemme <shortcutter@googlemail.com> - 2011-08-20 11:21 +0200
                Re: Using Enumerated Types as Array Indexes Andreas Leitgeb <avl@gamma.logic.tuwien.ac.at> - 2011-08-20 11:45 +0000
                Re: Using Enumerated Types as Array Indexes Robert Klemme <shortcutter@googlemail.com> - 2011-08-20 15:23 +0200
                Re: Using Enumerated Types as Array Indexes Andreas Leitgeb <avl@gamma.logic.tuwien.ac.at> - 2011-08-20 16:15 +0000
                Re: Using Enumerated Types as Array Indexes Eric Sosman <esosman@ieee-dot-org.invalid> - 2011-08-17 21:34 -0400
                Re: Using Enumerated Types as Array Indexes Robert Klemme <shortcutter@googlemail.com> - 2011-08-18 07:58 +0200
                Re: Using Enumerated Types as Array Indexes Arved Sandstrom <asandstrom3minus1@eastlink.ca> - 2011-08-18 06:29 -0300
                Re: Using Enumerated Types as Array Indexes RedGrittyBrick <RedGrittyBrick@spamweary.invalid> - 2011-08-18 10:47 +0100
                Re: Using Enumerated Types as Array Indexes Lew <lewbloch@gmail.com> - 2011-08-18 11:35 -0700
                Re: Using Enumerated Types as Array Indexes Arved Sandstrom <asandstrom3minus1@eastlink.ca> - 2011-08-18 18:30 -0300
                Re: Using Enumerated Types as Array Indexes Robert Klemme <shortcutter@googlemail.com> - 2011-08-19 14:57 +0200
                Re: Using Enumerated Types as Array Indexes Andreas Leitgeb <avl@gamma.logic.tuwien.ac.at> - 2011-08-19 20:10 +0000
                Re: Using Enumerated Types as Array Indexes Arved Sandstrom <asandstrom3minus1@eastlink.ca> - 2011-08-19 19:12 -0300
                Re: Using Enumerated Types as Array Indexes Robert Klemme <shortcutter@googlemail.com> - 2011-08-20 00:26 +0200
                Re: Using Enumerated Types as Array Indexes Andreas Leitgeb <avl@gamma.logic.tuwien.ac.at> - 2011-08-19 22:59 +0000
          Re: Using Enumerated Types as Array Indexes Arne Vajhøj <arne@vajhoej.dk> - 2011-08-17 21:34 -0400
            Re: Using Enumerated Types as Array Indexes Arne Vajhøj <arne@vajhoej.dk> - 2011-08-17 21:46 -0400
              Re: Using Enumerated Types as Array Indexes markspace <-@.> - 2011-08-17 19:51 -0700
    Re: Using Enumerated Types as Array Indexes David Lamb <dalamb@cs.queensu.ca> - 2011-08-17 08:29 -0400
      Re: Using Enumerated Types as Array Indexes Robert Klemme <shortcutter@googlemail.com> - 2011-08-17 16:04 +0200
      Re: Using Enumerated Types as Array Indexes Arne Vajhøj <arne@vajhoej.dk> - 2011-08-17 21:51 -0400
  Re: Using Enumerated Types as Array Indexes Niklas Holsti <niklas.holsti@tidorum.invalid> - 2011-08-17 11:24 +0300
    Re: Using Enumerated Types as Array Indexes Arne Vajhøj <arne@vajhoej.dk> - 2011-08-17 21:55 -0400
      Re: Using Enumerated Types as Array Indexes Niklas Holsti <niklas.holsti@tidorum.invalid> - 2011-08-18 10:59 +0300
  Re: Using Enumerated Types as Array Indexes Roedy Green <see_website@mindprod.com.invalid> - 2011-08-17 22:09 -0700

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