Java Swing tutorials.
When a frame onscreen is closed by a user, frame gets hidden by defauly. Though it is visible, still the frame is present and it might be made visible by the program once again. If different behavior is needed on your partm then either get registered the window listener which controls the window closings or default close behavior could be specified by the help of method setDefaultCloseOperation. Both of them could also be done.
Given values shall be there for setDefaultCloseOperation