public void loadTileImages() {
        // keep looking for tile A,B,C, etc. this makes it
        // easy to drop new tiles in the images/ directory
        tiles = new ArrayList();
        char ch = 'A';
        while (true) {
            String name = "tile_" + ch + ".png";
            File file = new File("images/" + name);
            if (!file.exists()) {
                break;
            }
            tiles.add(loadImage(name));
            ch++;
        }
    }