public void addStop(int regency,int pid){
  HashSet<Integer> pids=stops.get(regency);
  if (pids == null)   pids=new HashSet<Integer>();
  pids.add(pid);
  stops.put(regency,pids);
}

public void addStop ( int regency , int pid ) { HashSet < Integer > pids = stops . get ( regency ) ; if ( pids == null ) pids = new HashSet < Integer > ( ) ; pids . add ( pid ) ; stops . put ( regency , pids ) ; }
keep information about an incoming stop message
