List<Rectangle> foursides = [...]
// Surface of all rectangles with a length and width greater than 2
int surface = foursides.stream().filter( (Rectangle v) -> v.width > 2 && v.height > 2). //
        mapToInt( (Rectangle v) -> v.width * v.height).sum();

// Parallel conversion from Rectangle to Rectangle2D.Double
Set<Rectangle2D.Double> foursides2D = foursides.stream().parallel(). //
        map(v -> new Rectangle2D.Double(v.x, v.y, v.width, v.height)).//
        collect(Collectors.toSet() );