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Re: Exception Handling

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On 3/11/2012 4:23 PM, Novice wrote:
> Patricia Shanahan<pats@acm.org>  wrote in
> news:S7GdnRomTdoRu8DSnZ2dnUVZ_sWdnZ2d@earthlink.com:
>
>> On 3/11/2012 2:54 PM, Novice wrote:
>>> Lew<noone@lewscanon.com>   wrote in news:jjipli$np7$1
> @news.albasani.net:
>> ...
>>>> It is common and frequently useful to create an application-specific
>>>> checked exception. Again, and I've said this many times, think about
>>>> what will be useful when troubleshooting a problem. Many times, a
>>>> custom exception is useful. It says that the underlying exception has
>>>> been caught, logged and wrapped.
>>>>
>>> But how is a custom FooException better than a good ol'
>>> IllegalArgumentException? I'm not quite getting that yet.
>>
>> Generally, you should use different Exception subclasses for cases that
>> may need different handling, so that callers can set up appropriate
>> catch blocks.
>>
>> Regardless of the conditions under which you choose to generate
>> IllegalArgumentException, many methods you will be calling use it to
>> indicate an illegal argument condition that has not yet been logged or
>> otherwise reported.
>>
>> If you also use it to indicate exceptions that have already been
> logged,
>> you risk either repeated logging of the same issue, or failure to log.
>>
>> On the other hand, if you create an Exception subclass that you only
>> throw after logging the underlying problem, there is no ambiguity.
>> Callers have to deal with the consequences of the failure, but should
>> only generate log messages if they have something to add. The
> underlying
>> problem has already been logged.
>>
> I'm sure this will seem like good advice when I understand it but it's
> still vague to me.
>
> It would really help if you could suggest a concrete example or two that
> show when to use a custom exception and why it's better.
>

Using the same exception for "illegal argument" and "already logged and
wrapped" is unlikely to get you into much trouble in a short program
viewed for a few minutes.

The potential trouble comes when you have a large program, too large to
read the whole thing before making a change, and it is being modified by
a programmer who does not know, or does not remember, that the exception
has those two meanings.

That makes it difficult to illustrate in a small example.

Remember that a lot of what you are being told, both in the newsgroup
and in the articles you are reading, is based on experience with
maintaining large programs over many years.

Patricia

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Thread

Exception Handling Novice <novice@example..com> - 2012-03-11 01:51 +0000
  Re: Exception Handling Lew <noone@lewscanon.com> - 2012-03-10 18:39 -0800
    Re: Exception Handling Arved Sandstrom <asandstrom3minus1@eastlink.ca> - 2012-03-11 11:53 -0300
      Re: Exception Handling Lew <noone@lewscanon.com> - 2012-03-11 10:51 -0700
        Re: Exception Handling Arved Sandstrom <asandstrom3minus1@eastlink.ca> - 2012-03-11 16:35 -0300
    Re: Exception Handling Novice <novice@example..com> - 2012-03-11 17:05 +0000
      Re: Exception Handling Lew <noone@lewscanon.com> - 2012-03-11 10:53 -0700
        Re: Exception Handling Novice <novice@example..com> - 2012-03-11 20:36 +0000
      Re: Exception Handling Lew <noone@lewscanon.com> - 2012-03-11 11:07 -0700
        Re: Exception Handling Arved Sandstrom <asandstrom3minus1@eastlink.ca> - 2012-03-11 17:00 -0300
          Re: Exception Handling Novice <novice@example..com> - 2012-03-11 22:02 +0000
        Re: Exception Handling Arivald <NOSPAMarivald@interia.pl> - 2012-03-11 21:03 +0100
          Re: Exception Handling Arved Sandstrom <asandstrom3minus1@eastlink.ca> - 2012-03-11 18:31 -0300
        Re: Exception Handling Novice <novice@example..com> - 2012-03-11 21:54 +0000
          Re: Exception Handling Patricia Shanahan <pats@acm.org> - 2012-03-11 15:26 -0700
            Re: Exception Handling Novice <novice@example..com> - 2012-03-11 23:23 +0000
              Re: Exception Handling Lew <noone@lewscanon.com> - 2012-03-11 16:52 -0700
                Re: Exception Handling Novice <novice@example..com> - 2012-03-12 17:16 +0000
                Re: Exception Handling Lew <noone@lewscanon.com> - 2012-03-13 08:31 -0700
              Re: Exception Handling Patricia Shanahan <pats@acm.org> - 2012-03-11 17:51 -0700
                Re: Exception Handling Novice <novice@example..com> - 2012-03-12 17:26 +0000
            Re: Exception Handling Arne Vajhøj <arne@vajhoej.dk> - 2012-03-12 14:49 -0400
          Re: Exception Handling Arved Sandstrom <asandstrom3minus1@eastlink.ca> - 2012-03-11 20:46 -0300
            Re: Exception Handling Novice <novice@example..com> - 2012-03-12 17:43 +0000
      Re: Exception Handling Patricia Shanahan <pats@acm.org> - 2012-03-11 11:14 -0700
        Re: Exception Handling Novice <novice@example..com> - 2012-03-11 22:35 +0000
          Re: Exception Handling Lew <noone@lewscanon.com> - 2012-03-11 16:58 -0700
            Re: Exception Handling Novice <novice@example..com> - 2012-03-12 15:44 +0000
              Re: Exception Handling Gene Wirchenko <genew@ocis.net> - 2012-03-12 10:34 -0700
      Re: Exception Handling Arivald <NOSPAMarivald@interia.pl> - 2012-03-11 20:34 +0100
        Re: Exception Handling Novice <novice@example..com> - 2012-03-11 22:36 +0000
    Re: Exception Handling Arne Vajhøj <arne@vajhoej.dk> - 2012-03-12 14:41 -0400
  Re: Exception Handling Arne Vajhøj <arne@vajhoej.dk> - 2012-03-12 14:37 -0400
    Re: Exception Handling Novice <novice@example..com> - 2012-03-12 22:43 +0000
      Re: Exception Handling Lew <lewbloch@gmail.com> - 2012-03-12 16:11 -0700
      Re: Exception Handling Arivald <NOSPAMarivald@interia.pl> - 2012-03-13 00:54 +0100
        Re: Exception Handling Arved Sandstrom <asandstrom3minus1@eastlink.ca> - 2012-03-13 06:05 -0300

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