public void saveAsPng() {
    WritableImage image = barChart.snapshot(new SnapshotParameters(), null);

    // TODO: probably use a file chooser here
    File file = new File("chart.png");

    try {
        ImageIO.write(SwingFXUtils.fromFXImage(image, null), "png", file);
    } catch (IOException e) {
        // TODO: handle exception here
    }
}