private LecturasDAO getLecturasDAO()
 {
     if (lecturasDAO == null)
     {
         lecturasDAO =  new LecturasDAO();
     }
     return lecturasDAO;
 }
 //Constructor
 private ControlTanquesCore()
 {
     controlCombustibleDAO = new ControlCombustibleDAO();
     lecturasDAO = new LecturasDAO();
     comprasCombustibleDAO = new CompraCombustibleDAO();
 }