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Re: Exception Handling

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Novice wrote:
> Are you envisioning that our hypothetical Foo would have a single
> FooException that it wraps around everything that percolates up from the
> lower levels? Or would there be a bunch of FooExceptions, each handling
> different sorts of problems?

Quite often a single exception type suffices. You would only add another if 
there were a crying need for it.

> And what happens with logging? Do we just log the error as an
> IllegalArgumentException (or whatever) when we find it at the low level?

Did you read Patricia's advice on this very matter?

> Or do we also log it again, this time as a FooException, when we deal
> with it at the higher levels? I'm uneasy about writing what are
> effectively redundant messages to the log.

Patricia recommended, and I agree, that the custom exception serve as a signal 
that the lower-level problem has been logged. Remember?

> For what it's worth, I've cobbled together a CrashDialog class which my
> higher level methods, getLocalizedText() for example, displays when it
> handles an IllegalArgumentException() if it is thrown by getResources().
> (I'm now throwing IllegalArgumentException for nulls in the parameters as
> well as a failed getBundle()). In that case, the CrashDialog class says:

Is a failed 'getBundle()' really a programming error? Is it really an illegal 
argument? There was nothing illegal about the argument /per se/ if the 
resource just happened not to be available.

I suggest a checked exception, either 'IOException' or a subtype thereof, for 
a missing bundle, unless it really and truly is completely under programmer 
control. (And deployment-time issues never are.)

> ===================================================================
> Foo - Severe Error
>
> The program has to stop for the following reason: Certain language
> resources were not available.
>
> The problem has been logged and Technical Support will begin resolving
> the error shortly.
>
>            [Okay]
> ====================================================================
>
> The line about Technical Support resolving the problem shortly is
> somewhat fanciful since I'm the whole development team and the entire
> universe of end users at the moment ;-) I'm just envisioning what I'd say
> in a real production application.

Be careful of making promises because you must keep them.

Well, technically you don't have to, but do you want to be that guy?

> The bit about the language resources being unavailable is not completely
> satisfactory because it is probably not very helpful to a non-technical
> user but it seemed better to summarize the situation than to use the
> message from the exception; the user is even less likely to comprehend
> "the baseName must not be null" or "Unable to find resources for base
> name, com.novice.foo.FooTextzzz, and locale, jp_JP. Check the spelling of
> the base name". And I certainly don't want to display a stacktrace to the
> user!
>
> I've also logged the fact that the user clicked on okay to end the
> program as another SEVERE error. Mind you, that seems redundant and I'm

How is that any kind of error?

> inclined to remove that code again. I'm assuming that in the real world,
> one SEVERE error is going to be enough to get the attention of the
> appropriate people and producing two or three SEVERE errors about the
> same problem is not going to get the problem examined any sooner. Correct
> me if I'm wrong!

Don't worry, we will.

But you have a brain. What makes sense there? What would look funny to the ops 
guy?

Are you really thinking like a troubleshooter in the field, or like the 
programmer whose name that troubleshooter will curse?

> Now, that behavior wouldn't be standard for all cases. If the error is
> recoverable, the user would get different instructions that would lead
> him/her through whatever needs to be done to recover. And some errors
> might not be severe at all and just be informational. In those cases, the
> dialog might say "Information" instead of Severe Error and simply
> describe whatever workaround Foo adopted to get past the problem.
>
> I'm feeling good about the error handling and logging now. It's starting
> to fall into place for me, aside from the whole custom exception
> question.

What do you mean by "recoverable"? I mean able to show an error dialog and 
invite the operator to shut down. Is that not a valid program state?

-- 
Lew
Honi soit qui mal y pense.
http://upload.wikimedia.org/wikipedia/commons/c/cf/Friz.jpg

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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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