For a school project I have to design a system using UML, only I have ran into a problem.
Let's say that I have to design a (somewhat overcomplicated) vending machine. It has a class with the Creator pattern that makes controllers: VendingMachine. This class makes a SaleController object for every sale. The machine supports different kinds of payments, so the SaleController creates a Payment object. The job of this class is to request a payment with the CoinMachine or CardReader classes, based on a user input. However, it obviously needs a reference to the CardReader and CoinMachine objects, which are created by the the VendingMachine class.
Would it be better to create a public static readonly object reference in the VendingMachine? Or to pass an object reference to SaleController and then pass it on to Payment?
Thanks!
It seems to me that you need a PaymentService that is able to encapsulate such logic. This PaymentService would be the one deciding whether to use CardReader or CoinMachine to process the Payment object.
CardReader and CoinMachine should be dependencies of PaymentService. If you are using Spring, you could create CardReader and CoinMachine Beans by annotating them with @Component and in PaymentService you just need to make them dependencies (injected via @Autowired or constructor). If you are not using Spring or any other similar Inversion of Control Framework, your best option would be to create CardReader and CoinMachine instances on PaymentService and keep them as attributes.