The best and complete way to know what JDIC can is to browse the API documentation. Below are some keywords extracted from javadoc, but easier to read if you just want to have an overview.
Browser * Launch system default browser * Navigation: back, forward, stop, setURL * getContent(): get content of page (HTML), get URL
File * isEditable(File) * edit(): Launch associated editor to edit the given file * open(): Launch the associated application to open the given file * Icons1: get icon associated to a file on this system
Printing * isPrintable(File) * Prints a given file
Mail * Launches the message compose window of the default mailer
