/**
* Get rolling stock by road and number
*
* @param road RollingStock road
* @param number RollingStock number
* @return requested RollingStock object or null if none exists
*/
public RollingStock getByRoadAndNumber(String road, String number) {
String id = RollingStock.createId(road, number);
return getById(id);
}
public void changeId(RollingStock rs, String road, String number) {
_hashTable.remove(rs.getId());
rs._id = RollingStock.createId(road, number);
register(rs);
}