XOM API for Processing XML with Java

[Elliotte Harold <elharo AT metalab.unc.edu>]

John Cowan wrote:

> XOM violates this second expectation in its declarations of these method.
> Consider the toString() method.  The JavaDoc for Object class recommends
> that toString() returns a string which is "a concise but informative
> representation which is easy to read."  Now an object may be made a
> subclass of of Element in order to give it a natural representation
> in XML.  This does not mean, however, that the most informative
> representation is one that is suitable for a generic XML element.
> If the class is an application class, a suitable representation ought
> to be relevant to the application.

That change has already been made in Element in CVS at Steve's request. 
I wouldn't be hugely averse to making the change elsewhere if someone 
actually needed it.

> Likewise, the various equals() methods require that all subclasses of XOM
> classes use identity (==) as the meaning of equality.  This means that no
> subclass can function as a value class, because in value classes (String
> is a familiar example), equality is defined recursively as part-by-part
> equality rather than mere identity.  This is an unnecessary restriction
> on the freedom of application developers.  If there are parts of XOM
> that depend on this definition of the equals() method, they should be
> rewritten to use == directly.

This is a lot more serious. I'd need to check the XOM internals pretty 
carefully to make sure this is true. My concern is not so much direct 
use of equals(), as it is HashMaps and similar data structures, as well 
as third party code that depends on this contract. It's also been my 
experience that allowing subclasses to override equals() tends to 
violate the transitivity of equality. That is, it's very easy for 
a.equals(b) to be true but b.equals(a) to be false.

I'm not saying I couldn't be convinced here, but you'd need a damn good 
use case to convince me.

--
Elliotte Rusty Harold  elharo AT metalab.unc.edu
XML in a Nutshell 3rd Edition Just Published!
http://www.cafeconleche.org/books/xian3/
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