You've lot's of different ways of implementing this.  And you don't
have to require run-time compilation either, merely realease a public
API that the module creators can use.  We do this fairly extensively
with our products, releasing a fairly large API that users can click
into.

If you do want to go run-time, there are a few things you could
consider.  For instance, the Mozilla orginazation has a great pure-Java
JavaScript engine called Rhino (very stable, been around along
time)--go to http://mozilla.org/rhino.  There are engines for almost
every language around, including Java.  JavaWorld ran a comparison of
different engines a couple years back : http://linkfrog.net/daao

Walter Gildersleeve
Freiburg, Germany

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Take a look at Beanshell. It is a lightweight scripting language that
is very close to Java. This closeness makes it work very well with
standard Java objects.

If you want to build such an extendable model, it might also be worth
to take a look at the OSGi specifications. They form the foundation of
the Eclipse IDE. The OSGi specifies a small framework that manages the
modularity and lifecycle issues of a plugin based model.

Kind regards,

  Peter Kriens