public Stack<Point2D> hull(){
  Stack<Point2D> s=new Stack<Point2D>();
  for (  Point2D p : hull)   s.push(p);
  return s;
}

public Stack < Point2D > hull ( ) { Stack < Point2D > s = new Stack < Point2D > ( ) ; for ( Point2D p : hull ) s . push ( p ) ; return s ; }
returns the extreme points on the convex hull in counterclockwise order .
