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Re: About using assertion

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From	tmcd@tmcd-p4-linux.austin.tx.us (Tim McDaniel)
Newsgroups	comp.lang.java.programmer
Subject	Re: About using assertion
Date	Thu, 19 May 2011 00:32:12 -0500
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In article <92r0e9F6lvU1@mid.individual.net>,
Robert Klemme  <shortcutter@googlemail.com> wrote:
>On 09.05.2011 18:11, Lew wrote:
>> public class Foo
>> {
>> public double sqrt( double arg )
>> {
>> if ( arg < 0.0 )
>> {
>> throw new IllegalArgumentException(
>> "sqrt(): negative argument "+ arg );
>> }
>> assert arg >= 0.0; // precondition
>>
>> double result;
>> // rest of algorithm ...
>> return result;
>> }
>> }
>
>Lew, I am not sure what you tried to convey with this posting.  I for my 
>part would say that the assert is a tad too much here since the if 
>clause before that gives me enough "confidence" that arg is actually >= 
>0 at that line.  If it isn't then I have bigger problems than 
>calculating square roots of negative numbers. :-)

Consider

    Foo.sqrt(Double.NaN)

The "if" fails, but if assertions are enabled, the "assert" catches
it.  This might be an illustration that an assertion can be useful
even if you have "confidence" that it could never fire.

(As a tangent, I'm not sure whether "Foo.sqrt(-0.0)" should throw an
exception or not.)    

-- 
Tim McDaniel; Reply-To: tmcd@panix.com

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