I have some simple optical design tools that I make available
on the web.  Up to now, I have been delivering them in versions
for 1.4.2 and 1.5.0.  To do that, I have been using Netbeans
for daily development (1.5.0) and Sun ONE Studio sor simple
compilation and test (1.4.2), although I'm not sure that is
100% effective as the libraries used may still be the 1.5 set.

A friend has suggested that I start thinking about delivering
a version in 1.6 as well.  Obviously, my methodology cannot
easily be extended.

Is there a way I can easily shift between versions?  I think
what I'm talking about is perhaps a simple commmand sequence
that I can use to shift back and forth between the versions.
This would imply that I want to compile and run on the
different versions -- regression test on the old, at least.
That would mean that Netbeans would have to work with the
different Java version as well.

Multiple platforms is not a solution for me.