Past exam of the year 1 of the computer science course of the University of Oxford / 2016 / Imperative programming / 7 / c / Solution

The system uses the observer pattern with a pull-style update. Equipment provides the subject interface and stores registered observers; GymEquipment is the concrete subject. Functionality is the observer interface, with Performance and Prediction as concrete observers. Their constructors subscribe them with addFunctionality(this).

When GymEquipment.updateUserMeasures is called, it first updates both measurements through super, then calls notifyFunctionalities. Every subscribed observer receives update() and reads the new measurements from its stored equipment reference. Performance calculates the current score; Prediction calculates the score at time time+5, keeping the other quantities fixed. Since observers are prepended to a list, notification follows reverse registration order.

The source has two independent implementation defects. deleteFunctionality(f) computes _functionalities diff List(f) but does not assign it back, so it does not actually unsubscribe anything. The prediction message also contains a physical newline inside an ordinary quoted Scala string in the PDF; executable code must join that string, concatenate pieces, or use a multiline string. Neither issue changes the intended observer pattern. The source's score is treated as the specified arithmetic expression, not as an independently validated physiological model.