すべてが黒です。
btnFullScreen.addActionListener(new ActionListener() {
@Override
public void actionPerformed(ActionEvent event) {
GraphicsEnvironment ge = GraphicsEnvironment.getLocalGraphicsEnvironment();
GraphicsDevice gd = ge.getDefaultScreenDevice();
if (gd.isFullScreenSupported()) {
gd.setFullScreenWindow(frame);
}
}
});