Inheritance and Polymorphism

This lesson covers inheritance and polymorphism -- two of the four pillars of Object-Oriented Programming -- as required by the OCR A-Level Computer Science (H446) specification. These concepts enable code reuse, extensibility, and flexible design.

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What is Inheritance?

Inheritance is the mechanism by which one class (the subclass or child class) can inherit the attributes and methods of another class (the superclass or parent class). The subclass can then extend or modify the inherited behaviour.

Inheritance models an "is-a" relationship:

• A Dog is a Animal
• A SavingsAccount is a BankAccount
• A Circle is a Shape

Term	Definition
Superclass (parent/base class)	The class being inherited from.
Subclass (child/derived class)	The class that inherits from the superclass.
Inheritance	The mechanism of one class acquiring the attributes and methods of another.

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Single Inheritance

In single inheritance, a subclass inherits from exactly one superclass.

Pseudocode Example

CLASS Animal
    PRIVATE name: STRING
    PRIVATE age: INTEGER

    PUBLIC PROCEDURE new(n: STRING, a: INTEGER)
        name = n
        age = a
    END PROCEDURE