Sun Java is the most popular programming language used in University Computer Science labs.
In order to develop applications for BlackBerry, you will need the basics and access to BlackBerry Application Program Interface (API). That will allow you to develop programs that fully use the internal workings of the BlackBerry.
Or, if you don't want to make money off it. There are some people on here who like to try their hand at app-making, hook up with one of them and it may just be a fun project.