jframe full screen

frame.setExtendedState(JFrame.MAXIMIZED_BOTH);

// Getting fullscreen **effect** by extending the frame either direction.
frame.setExtendedState(JFrame.MAXIMIZED_BOTH); 
frame.setUndecorated(true);

frame.setExtendedState(JFrame.MAXIMIZED_BOTH); 
frame.setUndecorated(true);
frame.setVisible(true);