public Polygon(PolygonPoint p1,PolygonPoint p2,PolygonPoint p3){
  p1._next=p2;
  p2._next=p3;
  p3._next=p1;
  p1._previous=p3;
  p2._previous=p1;
  p3._previous=p2;
  _points.add(p1);
  _points.add(p2);
  _points.add(p3);
}

public Polygon ( PolygonPoint p1 , PolygonPoint p2 , PolygonPoint p3 ) { p1 . _next = p2 ; p2 . _next = p3 ; p3 . _next = p1 ; p1 . _previous = p3 ; p2 . _previous = p1 ; p3 . _previous = p2 ; _points . add ( p1 ) ; _points . add ( p2 ) ; _points . add ( p3 ) ; }
to create a polygon we need atleast 3 separate points
