Some of android's opencv functions return or have a MatOfPoint (or MatOf*) parameter. If somehow you have to manipulate those point's you have to convert it to a List or array.
MatOfPoint mop = new MatOfPoint();
List<point> lp = mop.toList();
Point[] pArray = mop.toArray();
Intuition will say that the array method is probably faster but what are your experiences with this, have you tried both in real-world applications?