I understand your idea but I have finished my project (actually I believed that it is finished and now teacher want one of panels to be inside JScrollPane).
Shortly, When program runs frame with 3 combos is shown I also have global variable ViewPanel that represents south part of this frame (and initially is empty) When user selects combo item another panel function returning JPanel is called and that panel is added to ViewPanel which is then added to frame's south part. If users selects another combo item ViewPanel is cleaned and function reurning panel is called ...
Now, instead of adding this returned panel I can put it in JScrollPane and add that JScrollPane to JViewPanel and later call pack() option on but pack option ignores all Size settings and make things on its own hand???