The Observer pattern participants are:
Service: the subject abstraction, owning the current value and registeredCompanyreferences, and providing registration and notification operations.SomeService: the concrete subject, makingupdateValuenotify after establishing the new subject state.Company: the observer object interface, declaring themeth()callback.PrivateCompanyandPublicCompany, together with the extensionNonProfit: concrete observers, registering themselves, retaining their subject, and updating their own values on notification.
The printed
PrivateCompany starts with factor but uses factor in its callback; PublicCompany starts with factor but later uses . These are the actual source behaviors, not a uniform pricing rule inferred from their names. The subject stores a list and prepends new subscriptions, so notification occurs in reverse registration order. Dependence on the Company interface lets the subject notify new observer types without naming their concrete classes. The omitted ... portions in the printed figure do not prevent identifying these roles or implementing the added observer. Articles by others on the same topic
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