public Segment(Point start, Point end) {
    if (start == null || end == null)
        throw new IllegalArgumentException("Arguments can't be null");
    if (start.equals(end))
        throw new IllegalArgumentException("The points must differ");
    this.start = start;
    this.end = end;

}

public Point intersection(Segment another) {


    div = dy2 * dx1 - dx2 * dy1;

    if (Math.abs(div) < 1.0e-10)
        return null;
   
}

Problem is that when I want to print:

Segment first = new Segment(new Point(0, 0), new Point(0, 0));
            Segment second = new Segment(new Point(0, 0), new Point(0, 0));
            Point intersection = first.intersection(second);

            System.out.println(intersection.getX());
            System.out.println(intersection.getY());

appear NullPointerExceptionin case when I introduced all coordinates 0. How to solve this? Help please if anybody can. I not understand how to catch this exception or how to solve.

CodePudding user response：

public static Point SegIntersection(double x11, double y11, double x12, double y12,
                                    double x21, double y21, double x22, double y22)
    {
        double dx1 = x12-x11;
        double dy1 = y12-y11;
        double dx2 = x22-x21;
        double dy2 = y22-y21;
        double dxx = x11-x21;
        double dyy = y11-y21;
        double div, t, s;
  
        div = dy2*dx1-dx2*dy1;
        if (Math.abs(div) < 1.0e-10)  //better to compare abs(div) with small Eps
           return null;  //collinear case
        
        t = (dx1*dyy-dy1*dxx) / div;
        if (t < 0 || t > 1.0)
            return null; //intersection outside the first segment

        s = (dx2*dyy-dy2*dxx) / div;
        if (s < 0 || s > 1.0)  
            return null;  //intersection outside the second segment
        return new Point(x11   s * dx1, y11   s * dy1);
    }

Quick test

Note that function does not check overlapping of collinear segments, because problem statement ignores such case.