public final int compare(Object arg_a, Object arg_b) {
            Point a = (Point) arg_a;
            Point b = (Point) arg_b;
            if (a.x < b.x) {
                return -1;
            } else if (a.x > b.x) {
                return 1;
            } else {
                if (a.y < b.y) {
                    return -1;
                } else {
                    return 1;
                }
            }
        }