How to implement the idea of objects that access objects of other classes?

Sounds more like there's a Box (could just be a list) that takes Shift s, and an Employee has multiple collections of Shift s desiredShifts and actualShifts .

IMHO, I would use event-driven logic (e.g. Using property change listeners). Once an Employee instance is ready to submit the desired shifts, fire off an event (e.g. PropertyChangeEvent). And in this event object, pass the shift information and other relevant information.

From there, the receiver (i.e. WorkArrangement) can do what it pleases with such information (e.g. Firing off another change event that notifies the Manager that is has received shift information).

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