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From Chad La Joie <laj...@itumi.biz>
Subject Status of == vs equals()
Date Mon, 02 Aug 2010 14:11:38 GMT
So, while I don't have my access yet, Colm asked me if I'd take a look 
at the == vs equals() issue (relevant bugs: 40897[1], 45637[2], 46681[3])

My executive summary is that clearly, as things stand, the current code 
favors optimization over correctness.  Rarely is this a good thing.

Colm notes[4] that the reliance on intern'ed strings (and thus the 
ability to use ==) occurs sporadically throughout the code and not just 
within the ElementChecker implementations.  He specifically mentioned 
that the various C14N implementations, and indeed the == is used about 6 
times there for string comparison.

My recommendation then is two fold:
  - Ensure that nothing other than namespace bits are compared via ==. 
I don't know that this occurs but the code should definitely be reviewed 
to ensure that.

  - Create a new "NamespaceEqualityChecker" that provides methods for 
checking the various bits of a namespace (URIs, prefixes) and use it 
anywhere that either == or equals() is used today.  Implementations 
based on == and equals() would be provided with the default 
implementation being equals()-based.  A configuration option should then 
be made available to control which impl gets used.  Additionally, it 
might even be possible to add some smarts that could detect known "good" 
parsers that use interning and automatically use the == based 
implementation.

I do not recommend changing any part of the code without addressing the 
whole codebase (i.e. all the =='s need to be fixed or no change should 
be made) because of the possibility of creating new, unwanted, effects. 
  The current functionality is undesirable but better the devil you know.

I think that this should be addressed in the upcoming 1.4.4 release.  If 
quick consensus can be reached I'm willing to do the work with a window 
of time I have available over the next 2-3 weeks.

[1] https://issues.apache.org/bugzilla/show_bug.cgi?id=40897
[2] https://issues.apache.org/bugzilla/show_bug.cgi?id=45637
[3] https://issues.apache.org/bugzilla/show_bug.cgi?id=46681
[4] https://issues.apache.org/bugzilla/show_bug.cgi?id=45637#c1
-- 
Chad La Joie
http://itumi.biz
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