ScreenSaver.java

public final class ScreenSaver {
  public static final void main(final String[] args) throws Exception {
    UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName());

    final JFrame screenSaverFrame = new JFrame();
    screenSaverFrame.setDefaultCloseOperation(
      WindowConstants.EXIT_ON_CLOSE);
    screenSaverFrame.setUndecorated(true);
    screenSaverFrame.setResizable(false);
    screenSaverFrame.add(new JLabel("This is a Java Screensaver!",
      SwingConstants.CENTER), BorderLayout.CENTER);
    screenSaverFrame.validate();
    GraphicsEnvironment.getLocalGraphicsEnvironment()
      .getDefaultScreenDevice()
      .setFullScreenWindow(screenSaverFrame);
  }
}