XOM API for Processing XML with Java

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

At 6:29 AM -0700 10/22/02, Michael Fitzgerald wrote:
> Likewise, I think
>
> nu.xom.Node getNextSibling()
> nu.xom.Node getPreviousSibling()


You know, these methods have bothered me for a while, and I think 
I've finally put my finger on the problem, and maybe come up with a 
solution. The problem is that they don't really fit well into XOM's 
mostly indexed style of access. I don't find that code tends to use 
them a lot. Instead it just loops over all the children using an 
index. The ideas mostly come out of DOM, but XOM does things 
differently.  They also don't really belong in Attribute, where they 
always return null.

Perhaps instead, both of these methods should be replaced with the following:

public int position()

(Alternate names: indexOf(), index())

This method would return the current position of this node in its 
parent. I actually already have such a method, but it's package 
private. At least one person has asked for it already; and it might 
be useful in itself. Anybody who really needed to ask for the next or 
previous sibling of this node could just ask for 
node.getParent().getChild(node.position() + 1) or 
node.getParent().getChild(node.position() - 1). However, I really 
don't think this is a common use-case. DOM uses these for navigation. 
XOM doesn't.

This would also fix the attribute problem. Attributes do have an 
index already, which is purely for navigational convenience. I think 
it would make sense to use that here too.

Performance wise this would be no more expensive than what 
getNextSibling() and getPreviousSibling() do now, and could be more 
easily optimized if that proves important.

I also note that I use the current package private index() method 
quite frequently inside XOM. I think there might be call for it in 
some external packages for XPath, XSLT, XInclude, and so forth. I do 
need to expose enough functionality that not everything has to go 
into the core package. This feels to me like it would help a lot.

Open questions (assuming this is a good idea at all):

1. What should position() return if the parent is null? 0? -1? throw 
an exception?

2. What's the right name for this?

Thoughts?

--

+-----------------------+------------------------+-------------------+
| Elliotte Rusty Harold | elharo AT metalab.unc.edu | Writer/Programmer |
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|          XML in a  Nutshell, 2nd Edition (O'Reilly, 2002)          |
|              http://www.cafeconleche.org/books/xian2/              |
|  http://www.amazon.com/exec/obidos/ISBN%3D0596002920/cafeaulaitA/  |
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