public static double cos(Line2D aLine) {
    final double length = getLineLength(aLine.getX1(), aLine.getY1(), aLine.getX2(), aLine.getY2());
    if (length == 0) {
      throw new IllegalArgumentException(toString(aLine) + " has a zero length");
    }

    double deltaX = aLine.getX2() - aLine.getX1();
    return deltaX / length;
  }
public static double cos(Line2D aLine)