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From Gilles Sadowski <gil...@harfang.homelinux.org>
Subject Re: [Math] Usage of "NullPointerException" (Was: Re: svn commit: r981244 - in /commons/proper/math/trunk/src/main: ...)
Date Wed, 04 Aug 2010 13:28:02 GMT
> > > Why not in the new "exception" package?
> > > [The aim being to deprecate the old "MathRuntimeException".]
> > 
> > Sorry for that. I'm still not used to the new package.
> > Could you look at the various createXxxException factory methods in and
> > replace them by dedicated exceptions in the new package ? Obviously this
> > one is used only from one class but the older ones are more heavily used.
> 
> I've created "MathUnsupportedOperationException" (not committed yet). I was
> going to create "MathNullPointerException" but then looking at the usage in
> CM, I noticed that most checks for "null" result in throwing an
> "IllegalArgumentException"; exceptions to that rule appear in class
> "BigFraction". The usage should be consistent. I think that it is fine to
> use "MathIllegalArgumentException" everywhere. In which case I think that
> that we shouldn't have a "MathNullPointerException" at all (and never throw
> a "NullPointerException" explicitly from CM, so that when it happens, it
> will mean that some check is missing somewhere).

A simpler policy would be to not check for "null" and let the JVM do it. As
the JVM will do it anyway, it's a redundant check when the reference is not
null, i.e. most of time (in legitimate usage).
When the usage is wrong, the error is obvious and always the same ("null
reference") and the "NullPointerException" fully identify the problem. I
don't see why we should have a localized version of it. Yes, again, there
are detailed messages saying:
 "the covariance matrix cannot be null"
 "the function cannot be null"
 "the denominator cannot be null"
 etc.
But since any reference can potentially be "null", do you really intend to
have a specific meesage for every object?


Gilles

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