The Java GIS community is already host to several open-source toolkits of great capability. These toolkits provide a great number of services, and allow you the software developer to communicate with a wide varity of spatial information.

The UDIG framework goes the extra mile, providing a well structured application for you to extend. As a software developer you can focus on your tasks needed for your problem. The finding, connecting and display of spatial information can be someone else's problem.

Relationship with Libraries and Toolkits

You will find that uDig is set up as a platform allowing you to work "out of the box" with:

GeoAPI interfaces; these is a set of Java interfaces produced on commercial standards (provided by the Open Geospatial Consortium) and International standards (provided by the International Standards Origination)
GeoTools interfaces and implementation
JTS Toplogy Suite: provides the implementation of Geometry (ie the "Shapes") you see on the screen
...
Your own own domain objects

This is by no means a closed set; community plug-ins have experimented with:

R for stats analysis
C libraries like GDAL and OGR
C++ libraries like OSSIM

If you hear of a good toolkit or library please ask on the email list; we would be happy to help you hook it up.