Object-Oriented Design

This lesson covers the key concepts of object-oriented programming (OOP) and design: classes, objects, inheritance, polymorphism, encapsulation and abstraction. The OCR H446 specification requires you to understand these concepts and apply them to design problems.

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Core Concepts

Classes and Objects

Concept	Definition
Class	A blueprint or template that defines the attributes (data) and methods (behaviours) that objects of that type will have
Object	A specific instance of a class, with its own values for the class's attributes

Analogy: A class is like a cookie cutter (the template); objects are the individual cookies (each with its own specific details).

Example

Class: Dog
  Attributes: name, breed, age
  Methods: bark(), fetch(), sit()

Object 1: Dog("Rex", "Labrador", 5)
Object 2: Dog("Bella", "Poodle", 3)

Each object has its own values for name, breed and age, but they share the same methods defined in the class.

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The Four Pillars of OOP

1. Encapsulation

Encapsulation means bundling the data (attributes) and the methods that operate on that data together inside a class, and restricting direct access to the internal state from outside the class.