public static double sin(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 deltaY = aLine.getY2() - aLine.getY1();
    return deltaY / length;
  }
public static double sin(Line2D aLine)