iterate through each point on a line/path in java

Question

I'm new to using iterators and was wondering how one would iterate through each point on a line segment (Line2D.Double, to be precise) -- I need to check to see if each point on the line fulfills certain requirements.

Also, given a path object (like GeneralPath), how would you do the same thing (iterate through each point on the outline of the shape)?

Ideally I'd like something like this (with either a line or a path):

Line2D line = new Line2D.Double(p1,p2);
for (Point2D point : line)
{
   point.callSomeMethod();
}

Answer 1

There seems to be nothing in the Java API that makes Bresenham's algorithm user-visible. So I wrote a class that iterates over a line.

You can use it like this:

List<Point2D> points = new ArrayList<Point2D>();
Line2D line = new Line2D.Double(0, 0, 8, 4);
Point2D current;

for (Iterator<Point2D> it = new LineIterator(line); it.hasNext();) {
    current = it.next();
    points.add(current);
}

assertThat(points.toString(), 
    is("[Point2D.Double[0.0, 0.0], Point2D.Double[1.0, 0.0], " +
        "Point2D.Double[2.0, 1.0], Point2D.Double[3.0, 1.0], " +
        "Point2D.Double[4.0, 2.0], Point2D.Double[5.0, 2.0], " +
        "Point2D.Double[6.0, 3.0], Point2D.Double[7.0, 3.0], " +
        "Point2D.Double[8.0, 4.0]]"));

Answer 2

This will be slow because it will generate a new object for each point. If you need a faster solution, you might want to look into implementing the loop yourself, using the Bresenham algorithm .

Answer 3

Although your question is missing a lot of relevant info (ie I'm guessing a lot about your classes), the cleanest loop code is the foreach syntax:

GeneralPath path = ...;
for (Line2D.Double point : path.getPoints()) {
    // do something
}

Note however that you can not modify the object being iterated over with this kind of loop.

Answer 4

Check the type returned:

• PathIterator.SEG_MOVETO
• PathIterator.SEG_LINETO
• PathIterator.SEG_QUADTO
• PathIterator.SEG_CUBICTO
• PathIterator.SEG_CLOSE

Code:

PathIterator pi = path.getPathIterator(null);

while (pi.isDone() == false) {
    double[] coordinates = new double[6];
    int type = pi.currentSegment(coordinates);
    pi.next();
}

Answer 5

Use FlatteningPathIterator passing your Shape's path iterator.