Java Base Class from a library Possible?

Is it possible to have the ‘base class’ be in a Java library? I can’t seem to make it work. When I use the ‘edit project’ button to add a library to an agent, just the library is added and not the classes, and when I type the name of the class in the ‘base class’ field, I get an error on run. Is there any way to do this, or must the base class of a Java agent always reside in that agent?