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From: Jukka Lahtinen <jtfjdehf@hotmail.com.invalid>
Newsgroups: comp.lang.java.programmer
Subject: Re: Catching mulitple Exceptions in JDK 1.7
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Date: Wed, 03 Aug 2011 00:11:07 +0300
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Roedy Green <see_website@mindprod.com.invalid> writes:

> On Mon, 1 Aug 2011 23:54:34 -0700 (PDT), Lew <lewbloch@gmail.com>
> wrote, quoted or indirectly quoted someone who said :

>>In fact, if you only want to handle the IOException-ness of the exception, =
>>you wouldn't even bother mentioning 'SQLException' at all.  You'd just 'cat=
>>ch(IOException...)'. =20

> Here is a better example to illustrate my question:
> catch (IllegalArgumentException|IOException ex)

I think we understood your original question.

> What is the compile-time type of ex?
..
> What is the run-time type of ex if you got an IOException ?
..
> Or is there a rule that catch (a | b ex ) requires a to be a subclass
> of b, which would neatly sidestep the problem, but then the feature
> would not do anything useful.

That restriction wouldn't make any sense. If a extends b, there's no
point in catch (a|b) since you could do exactly the same with just
catch (b).

I haven't studied how it is handled, but I *suppose* the compile-time
type is the most specific Throwable that both a and b are subtype of
(probably in most cases Exception or some subclass of it). But of course
it wouldn't catch other subtypes that aren't either a or b or some
subtype of one of them.

And at runtime the JVM should know the exact type and you should be able
to ask it with instanceof like anywhere else, like I suggested in my
earlier followup.

if (ex instanceof Foo) {
   Foo bar = (Foo) ex;
   ...
}

But if you need to do that, you should't catch multiple types with
the same catch.

-- 
Jukka Lahtinen