jframe set fullscreen code example

Example 1: full screen in jframe

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

Example 2: jframe full screen

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