Question

Is there a class in the Java API that I can utilize to check if a line intersects a shape, given the starting and ending coordinates. I have tried playing around with Line2D objects, but the intersects() function for that class only seems to take in rectangular coordinates and Rectangle2D objects, which doesn’t suit my purposes as my shapes can have any number of sides.

Answer 1

Like @Dan said you can check is your line intersects borders of your Polygon but you don’t have to check intersect with everyline created by any two points from Polygon, just have to check intersection of your line with every pair of two point like (p1,p2), (p2,p3), ... , (p(N-1), pN), (pN, p1). Polygon isn’t created from all combination of points in array but from line from p1 to p2 connected with line from p2 to p3 and so on till line conected from pN to p1.

Some example here:

Line2D myLine = getMyLine() // some imagine method giving your line
Point2D[] polyPoints = getPolyPoints() // some imagine method giving point of your Polygon

boolean intersect = false;
for (int i = 0; i < polyPoints.length - 1; i++) {
   intersect = myLine.intersectsLine(polyPoints[i].getX(), polyPoints[i].getY(), polyPoints[i+1].getX(), polyPoints[i+1].getY());
   if (intersect) {
      break;
   }
}
if (!intersect) {
   intersect = myLine.intersectsLine(polyPoints[polyPoints.length - 1].getX(), polyPoints[polyPoints.length - 1].getY(), polyPoints[0].getX(), polyPoints[0].getY());
}

After execution of this code inside intersect you have value is your line intersects polygon or not.

If you accept situation when Polygon can contains a line and this still means that line (as a path) intersect the polygon then create java Polygon instance from your points (vertex) and just invoke:

if (!intersect) {
   intersect = myPolygon.contains(myLine.getP1()) || myPolygon.contains(myLine.getP2());
}