List<Rectangle> foursides = [...]

 // Java 1-7: Anonymous, inner class
Comparator<Rectangle> compr7 = new Comparator<Rectangle>() {
    @Override
    public int compare(Rectangle o1, Rectangle o2) {
        return o1.width - o2.width;
    }
};
foursides.sort (compr7);

// Java 8: Short definition as a Lambda
foursides.sort( (Rectangle r1, Rectangle r2) -> r1.width - r2.width);
foursides.sort( (r1, r2) -> r1.width - r2.width);

// Java 8: Use of static methods and references
foursides.sort(Comparator.comparingDouble(Rectangle::getWidth));
// Java 8: Use of default implementation from interface
foursides.sort(Comparator.comparingDouble(Rectangle::getWidth).reversed().
        thenComparing(Comparator.comparingDouble(Rectangle::getHeight)));