OOP

Quick Introduction

OOP is a single PHP idea you'll use in almost every backend project.

In this lesson you learn only oop — not five topics at once. By the end you can write a small working example and explain it in an interview.

We connect each lesson to our course projects: Login System, Blog CMS, REST API, Inventory, Employee Management, and E-Commerce Backend.

Business Problem

You're building the Employee Management. After a user signs in, you need oop working correctly before storing data or showing a dashboard.

Without understanding OOP, the team ships bugs: wrong totals, broken sessions, or type errors that only appear in production. This lesson fixes that with one clear pattern you can copy into your project today.

Core Concept

• OOP is one focused idea — learn it before mixing with other PHP topics.
• Use it in PHP 8.3+ with declare(strict_types=1); at the top of every file.
• Our course project (Employee Management) uses oop in real handlers.
• Run small scripts with php file.php after each change — don't just read.
• Interviewers ask for a one-minute explanation plus a tiny code sample.

Syntax

Core syntax for OOP. Every keyword below appears in production PHP — Laravel and Symfony use the same primitives under the hood.

declare(strict_types=1);

Keywords: declare · strict_types · namespace

Step-by-Step Example

Run this script locally. Change one value, run again, and watch what changes.

<?php
declare(strict_types=1);

namespace Shop\Catalog;

abstract class Sellable {
    public function __construct(protected readonly string $name, protected float $price) {}

    abstract public function lineTotal(int $qty): float;

    public function label(): string {
        return sprintf('%s ($%.2f)', $this->name, $this->price);
    }
}

final class Book extends Sellable {
    public function lineTotal(int $qty): float {
        return $this->price * $qty * 0.95; // 5% book discount
    }
}

echo (new Book('Clean Code', 39.99))->lineTotal(2);

Line by line

1. — part of the oop example; run the file to see the result.
2. declare(strict_types=1); — turns on strict type checking for this file.
3. namespace Shop\Catalog; — part of the oop example; run the file to see the result.
4. abstract class Sellable { — part of the oop example; run the file to see the result.
5. public function __construct(protected readonly string $name, protected float $price) {} — part of the oop example; run the file to see the result.

OOP OK

Real-World Example

In the Employee Management, oop appears in a single request handler — not spread across ten files. Keep the example small, test it with php, then paste the pattern into your project branch.

<?php
declare(strict_types=1);

// TODO: OOP exercise for Employee Management