public static Car getInstance(String typeOfCar, RegistrationNumber registrationNumber, int fuelCapacity, int fuelInCar, boolean carRented){
		String stringRepresentation = registrationNumber.toString() + fuelCapacity + fuelInCar + carRented;
		Car c = CARS.get(stringRepresentation);
		if (c != null) return c;
		
		if (typeOfCar.equalsIgnoreCase("small car")){
			c = new SmallCar(registrationNumber, fuelCapacity, fuelInCar, carRented);
		}else{
			c = new LargeCar(registrationNumber, fuelCapacity, fuelInCar, carRented);
		}
		CARS.put(stringRepresentation, c);
		return c;
	}