private Set<String> buildItemList(List<Offer> offers){
  Set<String> items=new TreeSet<String>();
  for (  Offer offer : offers) {
    items.add(offer.getItemName());
  }
  return items;
}

private Set < String > buildItemList ( List < Offer > offers ) { Set < String > items = new TreeSet < String > ( ) ; for ( Offer offer : offers ) { items . add ( offer . getItemName ( ) ) ; } return items ; }
creates an alphabetically sorted set of items for which offers exist
