I agree with Waverick. The simplest way to do this with NetBeans is to add a custom target to your build.xml. (By the way, by virtue of using NetBeans, you are using Ant, since NetBeans uses Ant to build your jar file.)
Waverick's Ant target seems to be designed to merge the compiled code from a different NetBeans project into the current project's jar file. My targets below do exactly what you are looking for.
To run this application from the command line without Ant, try:
java -jar "${dist.jar.resolved}"
