JFrame in full screen Java

Add:

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

If you want put your frame in full-screen mode (like a movie in full-screen), check these answers.

• How can I do full screen in Java on OSX
• Java setFullScreenWindow() keep on top

The classes java.awt.GraphicsEnvironment and java.awt.GraphicsDevice are used for put an app in full-screen mode on the one screen (the dispositive).

e.g.:

static GraphicsDevice device = GraphicsEnvironment
        .getLocalGraphicsEnvironment().getScreenDevices()[0];

public static void main(String[] args) {

    final JFrame frame = new JFrame("Display Mode");
    frame.setDefaultCloseOperation(WindowConstants.EXIT_ON_CLOSE);
    frame.setUndecorated(true);

    JButton btn1 = new JButton("Full-Screen");
    btn1.addActionListener(new ActionListener() {
        @Override
        public void actionPerformed(ActionEvent e) {
            device.setFullScreenWindow(frame);
        }
    });
    JButton btn2 = new JButton("Normal");
    btn2.addActionListener(new ActionListener() {
        @Override
        public void actionPerformed(ActionEvent e) {
            device.setFullScreenWindow(null);
        }
    });

    JPanel panel = new JPanel(new FlowLayout(FlowLayout.CENTER));
    panel.add(btn1);
    panel.add(btn2);
    frame.add(panel);

    frame.pack();
    frame.setVisible(true);

}

One way is to use the Extended State. This asks the underlying OS to maximize the JFrame.

setExtendedState(getExtendedState() | JFrame.MAXIMIZED_BOTH);

Other approach would be to manually maximize the screen for you requirement.

Dimension dim = Toolkit.getDefaultToolkit().getScreenSize();
setBounds(100, 100, (int) dim.getWidth(), (int) dim.getHeight());
setLocationRelativeTo(null);

But this has pitfalls in Ubuntu OS. The work around I found was this.

if (SystemHelper.isUnix()) {
    getContentPane().setPreferredSize(
    Toolkit.getDefaultToolkit().getScreenSize());
    pack();
    setResizable(false);
    show();

    SwingUtilities.invokeLater(new Runnable() {
        public void run() {
            Point p = new Point(0, 0);
            SwingUtilities.convertPointToScreen(p, getContentPane());
            Point l = getLocation();
            l.x -= p.x;
            l.y -= p.y;
            setLocation(p);
        }
    });
}

Dimension dim = Toolkit.getDefaultToolkit().getScreenSize();
setBounds(100, 100, (int) dim.getWidth(), (int) dim.getHeight());
setLocationRelativeTo(null);

In Fedora the above problem is not present. But there are complications involved with Gnome or KDE. So better be careful. Hope this helps.

Use setExtendedState(int state), where state would be JFrame.MAXIMIZED_BOTH.