Well, I guess you are doing this on the event dispatch
thread, which is also responsible for redrawing the GUI. So as long as your method runs, the GUI cannot be redrawn.
If that's the case, you will need to execute that code on a different thread.
Moving to our Swing forum...
The soul is dyed the color of its thoughts. Think only on those things that are in line with your principles and can bear the light of day. The content of your character is your choice. Day by day, what you do is who you become. Your integrity is your destiny - it is the light that guides your way. - Heraclitus