Abstract Classes and Interfaces

This lesson covers abstract classes and interfaces — two mechanisms for achieving abstraction in Object-Oriented Programming. These features enforce structure in class hierarchies and are fundamental to designing large-scale, maintainable software systems.

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Abstraction Revisited

Abstraction is the process of hiding complex implementation details and exposing only the essential features of an object. It allows programmers to work with high-level concepts without needing to understand every internal detail.

Consider a car: you interact with the steering wheel, pedals, and gear stick (the interface), but you do not need to understand the internal combustion engine (the implementation).

In OOP, abstraction is achieved through:

• Abstract classes — classes that cannot be instantiated directly and may contain abstract methods.
• Interfaces — specifications of methods that a class must implement.

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Abstract Classes

An abstract class is a class that:

1. Cannot be instantiated — you cannot create objects directly from it.
2. May contain abstract methods — methods declared but not implemented.
3. May contain concrete methods — methods with full implementations that subclasses inherit.

Abstract classes serve as templates that force subclasses to implement specific behaviour.

Pseudocode Example