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Programming

Inheritance and evaluating the object-oriented approach

  • 3 things to know
  • AS Unit 1

Overview

Method overriding, superclass with two sensible subclasses and class hierarchy.

What you need to know

Answer each one before you reveal it.

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Key term

Explain the is-a test for deciding whether inheritance is appropriate.

Evaluation

Give two advantages of the object-oriented approach.

Key term

Why does the object-oriented approach make maintenance easier?

Questions from this subtopic

Each one with the model answer underneath.

  1. 1

    Define inheritance.

    Model answer

    Inheritance is the mechanism by which a new class takes on the attributes and methods of an existing class, and may then add further ones of its own or change what it has received.

  2. 2

    What names are given to the two classes in an inheritance relationship?

    Model answer

    The class being inherited from is called the superclass, parent or base class, and the class inheriting from it is called the subclass, child or derived class.

  3. 3

    Give one reason inheritance reduces the amount of code that has to be written.

    Model answer

    Anything common to several kinds of object is written once in the superclass, and each subclass inherits it rather than repeating it.

  4. 4

    What is method overriding?

    Model answer

    Method overriding is the replacement of an inherited method by a subclass's own version, so that objects of the subclass behave differently while the method keeps the same name.

  5. 5

    Give an example of a superclass with two sensible subclasses.

    Model answer

    A superclass called Account could have the subclasses Current Account and Savings Account, each inheriting the balance attribute and adding rules of its own.

  6. 6

    What is a class hierarchy?

    Model answer

    A class hierarchy is the tree of classes formed when subclasses inherit from a superclass and are themselves inherited from, with the most general class at the top.

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