IPA IP 2021 Question 41

Object orientation — classes and inheritance are the defining concepts of object orientation, which builds software from reusable components.

In object orientation, data and the procedures that act on it are encapsulated together in objects. A class is the template from which objects are made, and inheritance lets a new class (a subclass) take over the attributes and methods of an existing class (its superclass) and add or change only what differs. Classes thus become components that other programs can reuse, and inheritance reuses existing code instead of writing it again, which raises the productivity of development.

Answer (a)

Why not others:

• •(b) Structuring — divides a system into functions top-down and builds programs from the three control structures (sequence, selection, iteration); it has no classes or inheritance
• •(c) Process-oriented approach — designs a system around its business processes, the flow of processing, with data designed afterwards to serve each process; it is not built on classes and inheritance
• •(d) Prototyping — builds a trial model early to confirm requirements with users; it is a development model, not a way of turning software into reusable components

Key rule: Class, instance, encapsulation, inheritance and polymorphism are the vocabulary of object orientation; reuse through classes and inheritance points to it.

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