More sophisticated double-buffered rendering

DB.java

    private VolatileImage drawImage = null;
    private int drawImageWidth = 800;
    private int drawImageHeight = 600;

    public void render(BufferStrategy strategy) {
        if (drawImage == null) {
            drawImage = createVolatileImage(drawImageWidth, drawImageHeight);
        }
        Graphics2D drawGraphics = (Graphics2D) drawImage.getGraphics();
        // TODO: use `drawGraphics` to draw game graphics (background, platforms, player, etc.)

        // render a single frame:
        do {
            do {
                Graphics2D renderGraphics = (Graphics2D) strategy.getDrawGraphics();
                renderGraphics.drawImage(drawImage, 0, 0, null);
                renderGraphics.dispose();
            } while (strategy.contentsRestored());
            strategy.show();
        } while (strategy.contentsLost());
        Toolkit.getDefaultToolkit().sync();
    }