public void addHole(Polygon poly){
  if (_holes == null) {
    _holes=new ArrayList<Polygon>();
  }
  _holes.add(poly);
}

public void addHole ( Polygon poly ) { if ( _holes == null ) { _holes = new ArrayList < Polygon > ( ) ; } _holes . add ( poly ) ; }
assumes : that given polygon is fully inside the current polygon
