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From: "Phil Steitz" <phil.ste...@gmail.com>
Sent: Friday, August 06, 2010 3:34 AM
To: "Commons Developers List" <dev@commons.apache.org>
Subject: Re: [Math] Usage of "NullPointerException"
Gilles Sadowski wrote:
The added value that I see is that an IAE designating which argument
that cannot be null is in fact null gives more specific information
to the caller (or production support person examining logs) than
just a propagated NPE.
Well, my initial post reported the inconsistency of throwing either NPE
or
IAE as a result of checking for "null". If we take that NPE signifies a
bug
in CM, then we can have the policy of throwing IAE when null is
encountered
(and never explicitly throw NPE from CM).
+1 - that is what I meant by my option 1) above.
This was your option 1:
1) remove NPE wrappers, propagating uwrapped NPEs where the code
wraps and rethrows NPE today.
As I said, there are no wrappers around the NPE generated in CM. Either
"createNullPointerException" or "createIllegalArgumentException" is
called
and they generate the corresponding exception (not wrapped within
anything).
What I propose (as an alternative the "simple" policy) above is to create
a "NullArgumentException" that inherits from
"MathIllegalArgumentException".
This exception will be thrown whenever a null check fails (i.e. "null is
an
illegal argument"). To be consistent, we should never throw NPE from CM.
Is that what you meant to agree with?
There may be some cases where it makes sense to propagate NPEs
directly. I don't see any in the code now, but I would not rule it
out for the future. I am fine, however, dispensing with
MathRuntimeException.createNullPointerException (that's what I meant
by "wrapped NPE." Technically, you are right, the resultant NPE is
not really "wrapped," just specialized.) Where we throw IAE today
with informative error message indicating which parameter was null,
I want to retain the error message.
There are actually quite a few places were we propagate NPEs directly. For
example PolynomialFunction does this pretty much everywhere that the
JavaDocs says that it throws a NPE.
Phil
Gilles
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