[Advanced-java] How To Determine The Appropriate Exception?

[Silvio L. de Morais]

I like this kind of discussions.
To keep on the same subject, I would like your opinions on
a simple technique I use sometimes.
Whenever I have a method that receives a generic base class
as parameter (could even be Object), and I have to call a
specific method defined on a derived class, I do this:

public void m1(ClassA ob)
{
   String x;
   try {
       x =
((ClassB)ob).someMethodOfClassBNotDefinedInClassA();
   }
   catch (ClassCastException cce) {
   {
       x = "Default Value";
   }
   …	
}

My rationalization of this is: 'Most of the time the cast
will be correct, and I will not have to use the more
expensive "instanceof" operator all the time'. But I was
criticized before on a code review because it is not a good
use of Exceptions.
What do you guys think?

--- David Rosenstrauch <david.rosenstrauch@aleri.com>
wrote:
> On Friday 08 August 2003 10:15 am, KCE wrote:
> >
> > Yeah, in fact, you can use the Exception base class:
> >
> > try {
> >    myObject.myMethod();
> > } catch(Exception e) {
> >    e.printStackTrace();
> > }
> >
> > Just try to avoid doing this whenever possible!  Its
> > really easy to wind up with exceptions flying
> everywhere
> > and NO IDEA where they came from!!!
> 
> 
> Yes, use the exception class.
> 
> But IMHO your response is off-base on 2 other points:
> 
> 1) "Just try to avoid doing this whenever possible!"  I
> couldn't disagree 
> more.  There's no need to "try to avoid" using
> exceptions.  Use them when 
> they're appropriate - they make for a clean flow of code.
>  Don't use them 
> when they're not appropriate.  I don't think I ever
> experienced this issue of 
> "exceptions flying everywhere and NO IDEA where they came
> from", and I've 
> been coding in Java for 8 years.
> 
> 2) You should never do this:
> 
> } catch(Exception e) {
>    e.printStackTrace();
> }
> 
> "Swallowing" an exception deep down in some method in the
> call stack instead 
> of propogating it up the call stack is a really bad idea.
>  It makes for 
> extremely buggy code where something dies deep down
> somewhere, but the 
> calling code (whether GUI or server) never knows about it
> or handles it 
> properly.  Furthermore, "handling" an exception by just
> printing the stack 
> trace is pretty useless.  A stack trace printed to the
> console is of no use 
> to an end user.  (Assuming they even know where to look
> to read it.)
> 
> 
> DR
> 
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