AbstractCar(RegistrationNumber registrationNumber, int fuelCapacity, int fuelInCar, boolean carRented){	
		this.registrationNumber = RegistrationNumber.getInstance(registrationNumber.getLetterIdentifier(), registrationNumber.getNumberIdentifier());
		if (RegistrationNumber.getInstance(registrationNumber.getLetterIdentifier(), registrationNumber.getNumberIdentifier()).equals(null))
		    throw new IllegalArgumentException("That is not a valid Registration Number.");
		
		this.fuelCapacity = fuelCapacity;
		if(fuelCapacity <= 0)
			throw new IllegalArgumentException("The fuel capacity is inappropriate.");
		
		this.fuelInCar = fuelInCar;
		if (fuelInCar > fuelCapacity || fuelInCar < 0)
			throw new IllegalArgumentException("The fuel in car is a unacceptable amount.");
		
		this.carRented = carRented;
	}