Try something like this:

String command = "zip file.zip file1 file2";
// the zip  syntax might be wrong...
Process p = Runtime.getRuntime().exec(command);

You can create  nicer sequences (with threads and all), but this should give
you an idea where to start...

or you can user the built-in java  zipping tool. go to
developer.java.sun.com/.../
compression/#code2 for a full guide