7.1 Inheritance & Polymorphism Overview

Note: This guide is written based on Java 21. For the most up-to-date and comprehensive details, please refer to the official Java Documentation.

Up to this point, we have explored the foundational concepts of classes and objects. In this chapter, we will delve into the core and essence of Object-Oriented Programming (OOP) in Java: Inheritance, ** Polymorphism**, ** Abstraction**, and ** Encapsulation**.

These four pillars are central not only in Java but across most modern, object-oriented languages. They provide the groundwork for writing highly reusable, maintainable, and robust code.

The 4 Pillars of Object-Oriented Programming

Object-oriented design and implementation are supported by these four powerful pillars:

1. Inheritance

   • Inheritance is the mechanism by which one class acquires the properties (fields) and behaviors (methods) of another class.
   • It significantly promotes code reusability and reduces redundancy. For example, a Sparrow class can inherit all characteristics of a general Bird class while adding its own specific traits.

2. Polymorphism

   • The word polymorphism means having many forms. In Java, it allows us to perform a single action in different ways.
   • It provides maximum flexibility by allowing methods to behave differently based on the actual object type calling them. Overloading and overriding are key implementations of polymorphism.

3. Abstraction

   • Abstraction is the process of hiding complex implementation details from the user and exposing only the essential features of an object.
   • It focuses on what an object does instead of how it does it. This is typically achieved using Abstract Classes or Interfaces.

4. Encapsulation

   • Encapsulation is the practice of wrapping data (variables) and code acting on the data (methods) together as a single unit or capsule (the class).
   • It restricts direct, unauthorized access to some of an object's components (data hiding), using access modifiers (public, private, etc.).

What We Will Cover in This Chapter

By mastering this chapter, you will learn how to build large-scale projects systematically and flexibly, assembling components like Lego blocks.

• 7.2 Inheritance: Using the extends keyword, understanding parent (super) and child (sub) classes.
• 7.3 Polymorphism: Method overriding (@Override), type casting of reference variables, and practical applications of polymorphism.
• 7.4 Abstraction & Interfaces: Utilizing the abstract keyword, defining and implementing interface structures.
• 7.5 Encapsulation & Access Modifiers: Protecting internal data state and best practices using getter and setter methods.

Let's blossom into a more advanced Java developer by navigating through Chapter 7, often considered the heart of Object-Oriented Programming!