Understanding Inheritance in Object-Oriented Programming with PHP

In object‑oriented programming (OOP), inheritance allows a subclass to acquire properties and methods from a superclass, promoting code reuse and modular design.

The article first presents a non‑inherited example where both Product and Book classes define their own $name, $price, and accessor methods, resulting in duplicated code.

class Product {<br/>    protected $name;<br/>    protected $price;<br/><br/>    public function __construct($name, $price) {<br/>        $this->name = $name;<br/>        $this->price = $price;<br/>    }<br/><br/>    public function getName() {<br/>        return $this->name;<br/>    }<br/><br/>    public function getPrice() {<br/>        return $this->price;<br/>    }<br/>}<br/><br/>class Book {<br/>    protected $title;<br/>    protected $author;<br/>    protected $price;<br/><br/>    public function __construct($title, $author, $price) {<br/>        $this->title = $title;<br/>        $this->author = $author;<br/>        $this->price = $price;<br/>    }<br/><br/>    public function getTitle() {<br/>        return $this->title;<br/>    }<br/><br/>    public function getAuthor() {<br/>        return $this->author;<br/>    }<br/><br/>    public function getPrice() {<br/>        return $this->price;<br/>    }<br/>}<br/><br/>// Usage<br/>$cloth = new Product("T-shirt", 20);<br/>echo "Cloth: " . $cloth->getName() . ", Price: $" . $cloth->getPrice() . "<br>";<br/><br/>$book = new Book("The Great Gatsby", "F. Scott Fitzgerald", 15);<br/>echo "Book: " . $book->getTitle() . " by " . $book->getAuthor() . ", Price: $" . $book->getPrice();

It then discusses the drawbacks of duplicating similar classes, especially when many product types are needed, leading to redundant, hard‑to‑maintain code.

To address this, the article refactors the code by creating a Product base class and letting Book extend it, adding only the specific $author property and related method, while reusing the inherited getName and getPrice methods.

class Product {<br/>    protected $name;<br/>    protected $price;<br/><br/>    public function __construct($name, $price) {<br/>        $this->name = $name;<br/>        $this->price = $price;<br/>    }<br/><br/>    public function getName() {<br/>        return $this->name;<br/>    }<br/><br/>    public function getPrice() {<br/>        return $this->price;<br/>    }<br/>}<br/><br/>class Book extends Product {<br/>    protected $author;<br/><br/>    public function __construct($name, $price, $author) {<br/>        parent::__construct($name, $price);<br/>        $this->author = $author;<br/>    }<br/><br/>    public function getAuthor() {<br/>        return $this->author;<br/>    }<br/>}<br/><br/>// Usage<br/>$cloth = new Product("T-shirt", 20);<br/>echo "Cloth: " . $cloth->getName() . ", Price: $" . $cloth->getPrice() . "<br>";<br/><br/>$book = new Book("The Great Gatsby", 15, "F. Scott Fitzgerald");<br/>echo "Book: " . $book->getName() . " by " . $book->getAuthor() . ", Price: $" . $book->getPrice();

The revised implementation demonstrates how inheritance enhances reusability, reduces redundancy, and enables polymorphic behavior, laying a solid foundation for other OOP concepts such as abstraction and encapsulation.