set fullscreen jframe code example

Example 1: set jframe fullscreen

GraphicsEnvironment graphics = 
		GraphicsEnvironment.getLocalGraphicsEnvironment();
        
GraphicsDevice device = graphics.getDefaultScreenDevice();
JFrame frame = new JFrame("Fullscreen");
device.setFullScreenWindow(frame);

Example 2: how to make JFrame full screen

If you have extended the class to JFrame then -
this.setExtendedState(JFrame.MAXIMIZED_BOTH);
IF not then - 
frame.setExtendedState(JFrame.MAXIMIZED_BOTH);