PHP Classes and Objects

Object-oriented programming (OOP) groups data and the code that works on it into one unit called a class.

Class and Object

A class is a plan or template, like the design of a car
An object is a real thing made from that plan, like one actual car
Properties are the data of an object (colour, model)
Methods are functions inside a class (start, stop)

Your First Class

Example

php

<?php
class Student {
    public string $name;
    public int $marks;

    public function result(): string {
        return $this->marks >= 40 ? "Pass" : "Fail";
    }
}

$s = new Student();
$s->name = "Ali";
$s->marks = 68;

echo $s->name . ": " . $s->result();

Output

Ali: Pass

new Student() creates an object
-> reaches a property or method of an object
$this means "this object" inside the class

Constructors

A constructor runs automatically when you create the object. It is the place to set starting values.

Example

php

<?php
class Product {
    public function __construct(
        public string $name,
        public float $price,
        public int $stock = 0
    ) {}

    public function label(): string {
        return "{$this->name} - Rs " . number_format($this->price);
    }
}

$fan = new Product("Ceiling Fan", 8500, 12);
echo $fan->label() . "<br>";
echo "In stock: " . $fan->stock;

Output

Ceiling Fan - Rs 8,500
In stock: 12

Writing public before the constructor parameters is called constructor promotion (PHP 8). It creates and fills the properties in one step.

Visibility

Keyword	Who can use the property or method
`public`	Everyone
`protected`	The class and its child classes
`private`	Only the class itself

Keep data private and give methods to change it safely:

Example

php

<?php
class BankAccount {
    private float $balance = 0;

    public function deposit(float $amount): void {
        if ($amount <= 0) {
            throw new InvalidArgumentException("Amount must be positive.");
        }
        $this->balance += $amount;
    }

    public function getBalance(): float {
        return $this->balance;
    }
}

$acc = new BankAccount();
$acc->deposit(5000);
$acc->deposit(2500);
echo "Balance: Rs " . $acc->getBalance();

Output

Balance: Rs 7500

Writing $acc->balance = 1000000; from outside would give an error, because the property is private.

Inheritance

A child class gets everything from its parent class and can add or change things. Use extends:

Example

php

<?php
class Person {
    public function __construct(protected string $name) {}

    public function introduce(): string {
        return "I am {$this->name}.";
    }
}

class Teacher extends Person {
    public function __construct(string $name, private string $subject) {
        parent::__construct($name);
    }

    public function introduce(): string {
        return parent::introduce() . " I teach {$this->subject}.";
    }
}

$t = new Teacher("Sir Imran", "PHP");
echo $t->introduce();

Output

I am Sir Imran. I teach PHP.

Frameworks like Laravel and WordPress plugins use classes everywhere. Understanding OOP makes them much easier to learn.

Exercise

Which keyword makes a property usable only inside its own class?