[jdom-interest] Java 5 planning

[Jason Hunter]

First off, I want to thank Rolf for investing his time in exploring the 
technical feasibility of a JDOM migration to a Java 5 baseline.  A few 
other people have explored the area in the past as well, and it feels 
like (especially with JDOM 1.1 now finished) we can look at this in earnest.

What I'd like to do here is take a high level view and ask some 
questions of our local Java 5 porting experts -- Rolf, Mattias, Victor, 
Gregor, and any others with experience porting widely-adopted projects 
to Java 5.

1. I think we can all agree the ideal scenario is to develop a drop-in 
replacement, a new JAR which (so long as you're on Java 5+) would let 
previously compiled code continue to work.  This would let us continue 
development as usual with a new release (call it 1.2 or 1.5 or 2.0) 
simply having a higher Java version requirement.  How far can we go down 
the road of embracing Java 5 while still maintaining this?

2. A less ideal scenario would require any previously compiled code to 
be recompiled against the new JAR, but wouldn't require any code 
changes.  This will cause some confusion and effort but to an acceptably 
small amount.  Rolf, you say your build requires a recompile and in 99% 
of cases doesn't require code changes.  Where are the gaps?  Can they be 
filled?

3. The fallback scenario is one where people will need to modify 
existing code in order to use the new version.  This will cause some 
pain, and should we follow this path I think we should look at what 
steps we can take to mitigate it.  Automated upgrade scripts?  A new 
package, like org.jdom5, so people can choose to use the old version or 
the new?  Other possibilities?

4. Lastly, I'd like to hear from people on what specific advantages 
they're looking for in an upgrade to a Java 5 baseline.

My answers:

I'll start with (4) because you need to know why before you know how.  I 
think people would most like to improve the return values of methods to 
be more specific.  For example, getChild() should return Element, 
getChildren() should return List<Element>, text.getParent() should 
return Element, doctype.getParent() should return Document, and so on. 
Are there other "big ticket" items?

On (1) I suspect that without a source recompile we can't adjust the 
method return types which is the core value of the upgrade.

On (2) from Rolf's README it looks like there are two areas likely to 
require code changes based on his port: the Filter.filter() change and 
the AttributeType enum.  Both seem like things to do if you're already 
requiring code changes but aren't things so valuable in and of 
themselves that we should require people do a code change.  Are there more?

-jh-