java - FullscreenWindow でウィンドウが表示されない

Question

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);
                }
            }
        });