@Override public int hashCode(){
  int hash=17;
  hash=31 * hash + month;
  hash=31 * hash + day;
  hash=31 * hash + year;
  return hash;
}

@ Override public int hashCode ( ) { int hash = 17 ; hash = 31 * hash + month ; hash = 31 * hash + day ; hash = 31 * hash + year ; return hash ; }
returns an integer hash code for this date .
