The problem is that you run your long running loop on the event dispatch thread. But this is the thread that must dispatch all events of the application like mouse or keyboard events but also repaint events that causes your user interface to get repainted every time it gets 'dirty'. That means, while your for-loop is running, the user interface is not repainted nor are any other events processed. Your UI freezes!
Your jButton5ActionPerformed method should return as soon as possible so that the event dispatch thread can process other events. Your long running operation should be run by a separate thread in the background.
A good starting point is the following tutorial about concurrency in Swing:
http://docs.oracle.com/javase/tutorial/uiswing/concurrency/
Maybe you can use the SwingWorker class to perform your background work:
http://docs.oracle.com/javase/6/docs/api/javax/swing/SwingWorker.html
