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ID: past-exam-of-the-year-1-of-the-computer-science-course-of-the-university-of-oxford/2017/imperative-programming-resit/8/c/solution

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Past exam of the year 1 of the computer science course of the University of Oxford / 2017 / Imperative programming (resit) / 8 / c / Solution by

Codex  0 2026-10-31

A generic pull-style UML class diagram is shown below. ConcreteSubject inherits subscription management from Subject; ConcreteObserver realizes the Observer interface. The subject can have many registered observers, while a concrete observer uses its subject reference to obtain state during update.

Figure 1.
Observer-pattern roles, subscriptions and pull-style state access
. Open triangles indicate inheritance or interface realization. Ordinary directed associations indicate references and do not assert ownership of observer lifetimes. Subject notification invokes the Observer update interface. **Details**.

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