How do I iterate on these lists at the same time?

Question

This is what I want to achieve:

    public ArrayList<Point> startPoints = new ArrayList<Point>();
    public ArrayList<Point> endPoints = new ArrayList<Point>();

            for (Point startPoint : startPoints) { // <-- How do I do I do 2 at the same time?
                 g.fillOval(startPoint .x, startPoint.y, 10, 10);
                 g.drawLine(startPoint .x, startPoint.y, endPoint.x, endPoint.y);
            }

Check this: http://stackoverflow.com/questions/15985266/how-to-iterate-through-two-arraylists-simultaneously — Juned Ahsan, Nov 02 '13 at 18:45

score 4 · Accepted Answer · answered Nov 02 '13 at 18:45

4

use a "normal" for with an index i.

// if list1 and list2 have the same length
for(int i = 0;i<list1.size();i++){
   list1.get(i); // do something with that
   list2.get(i); // do something else with that
}

answered Nov 02 '13 at 18:45

L.Butz

2,466
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score 0 · Answer 2 · answered Nov 02 '13 at 18:45

0

Try to use normal for loop instead of foreach

answered Nov 02 '13 at 18:45

user123454321

1,028
8
26

score 0 · Answer 3 · answered Nov 02 '13 at 18:45

If you are unable to change the data structures:

for (int i = 0; i < startPoints.size() && i < endPoints.size(); i++) {
    Point startPoint = startPoints.get(i);
    Point endPoint = endPoints.get(i);
    g.fillOval(startPoint.x, startPoint.y, 10, 10);
    g.drawLine(startPoint.x, startPoint.y, endPoint.x, endPoint.y);

}

score 0 · Answer 4 · answered Nov 02 '13 at 18:46

I would recommend, instead of relying on iteration to successfully stay in synch, to use a single Line class that contains two points. For each start and end point construct your Line object and insert it into an arraylist.

To get them out just iterate as follows:

for (Line line : lines) { // <-- How do I do I do 2 at the same time?
     g.fillOval(line.getStartPoint().x, line.getStartPoint().y, 10, 10);
     g.drawLine(line.getStartPoint().x, line.getStartPoint().y, line.getEndPoint().x, line.getEndPoint.y);
}

score 0 · Answer 5 · answered Nov 02 '13 at 18:46

You cannot do both at the same time using the 'foreach' for loop you have.

If you are sure the Lists are both the same size then use the loop:

        for (int i = 0; i < startPoints.size(); i++) { // <-- How do I do I do 2 at the same time?
             Point startPoint = startPoints.get(i);
             Point endPoint = endPoints.get(i);
             g.fillOval(startPoint .x, startPoint.y, 10, 10);
             g.drawLine(startPoint .x, startPoint.y, endPoint.x, endPoint.y);
        }

score 0 · Answer 6 · answered Nov 02 '13 at 18:51

0

Since your data (startPoint and endPoint) are related - put them within another class (say MyVector) that will have startPoint and endPoint members (of type Point). Having such structure you iterate over list of MyVector objects.

answered Nov 02 '13 at 18:51

Artur

7,038
2
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How do I iterate on these lists at the same time?

6 Answers6