Oop

By the end of this lesson you'll be able to model real things as classes — bundling their data and behaviour into objects with constructors, visibility, static members, constants, and readonly properties — the foundation of every modern PHP application.

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Part of the free Php course at LearnCodingFast — hands-on lessons with examples you run in your browser, plus practice exercises and a quick quiz.

What You'll Learn in This Lesson

1️⃣ Classes, Properties & Objects

Up to now your data has lived in loose variables. Object-oriented programming (OOP) bundles related data and the code that works on it into one unit. A class is the blueprint: it lists the properties (the data each object holds) and the methods (the things it can do). An object is a single thing built from that blueprint with the new keyword. You reach inside an object with the arrow operator - . Typing each property ( string $name ) tells PHP — and your editor — exactly what kind of value belongs there.

Notice $rex and $buddy are completely separate — each carries its own name and age . That independence is the whole point: one blueprint, many self-contained objects.

2️⃣ The Constructor, $this & Methods

Setting every property by hand is tedious. A constructor — the special method named __construct() — runs automatically the instant you write new , so an object is born ready to use. Inside any method, $this means "this particular object", so $this- name = $name stores the passed-in value on the object. A method is just a function that lives in the class and can use $this .

3️⃣ Visibility & Constructor Promotion

Each property has a visibility that decides who may touch it. public means anyone, anywhere; private means only code inside the same class ; protected is like private but also visible to classes that extend it. Hiding data behind private lets a class guarantee it stays valid — outsiders go through methods (a getter like getBalance() ) instead of poking the value directly. PHP 8's constructor property promotion declares the property and assigns the argument in one move: put the visibility keyword right in the constructor's parameter list and PHP does the $this- x = $x for you.

The whole class is just a constructor and two short methods, yet $balance can never be set to a nonsense value from outside — that's encapsulation , the real payoff of private .

4️⃣ Static Members & Class Constants

Most properties belong to an object . A static property or method belongs to the class itself — there's one shared copy and you reach it with Class::member , no new needed. From inside the class you write self:: to mean "this class" ( static:: is its close cousin that respects subclasses — handy once you use inheritance). A class constant ( const MAX = 100; ) is a fixed value attached to the class that can never change, written in UPPER_CASE by convention.

Now you try. The class below is almost complete — fill in each ___ using the 👉 hint, then run it and check it against the Output panel.

One more — this time the blanks are about static members. Fill them in so the shared counter works.

5️⃣ Readonly Properties

Some values should be set once and then frozen — an id , a created-at timestamp, a primary key. PHP 8.1's readonly keyword does exactly that: the property can be assigned a single time (almost always inside the constructor) and any later attempt to change it throws an error. It pairs perfectly with constructor promotion, giving you tamper-proof objects with almost no code.

📋 Quick Reference — PHP OOP

No code is filled in this time — just a brief and an outline. Write the class yourself, run it on onecompiler.com/php or your own machine, then check your result against the expected output in the comments. This is exactly the write-run-check loop you'll use on every real class.

Practice quiz

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