Past exam of the year 1 of the computer science course of the University of Oxford / 2016 / Imperative programming / 8 / c

For the factory method pattern, Manufacturer is the abstract creator and declares build(carType): Car; UKManufacturer and USManufacturer are concrete creators. Car is the abstract product interface, and Convertible, Family, and Sports are concrete products. Each national creator selects one product software class from carType and configures the national settings. The diagram does not contain distinct families of national product interfaces or several abstract product-creation operations, so abstract factory pattern is not the most precise identification of this single-operation design.

For the decorator pattern, Car is also the component interface. Convertible, Family, and Sports are concrete components; Option is the abstract decorator, both a subtype of Car and associated with a wrapped Car. DieselEngine, AlarmSystem, and AutomaticTransmission are concrete decorators. Each delegates baseline behavior to its wrapped car, augments description, and adds its surcharge to price. National properties should delegate unchanged through decorators.

A customer can compose options, for example new AlarmSystem(new DieselEngine(baseCar)). Every layer remains usable through the Car interface; each layer adds its own description and price contribution. Factory methods choose/configure the base car, and decorators compose optional additions without requiring a subclass for every option combination. If applying each option at most once is required, enforce that as a separate ordering constraint; unrestricted decorator nesting alone permits repeated options.