OOP Basics: Constructor

A constructor is a special, so-called "magic" method within a class that triggers automatically at the moment you create a new instance of the class using the new command. Its main task is to give the object initial values right at birth (initialization), which ensures that the object is ready for use without any additional settings.

Imagine the constructor as a factory robot on an assembly line. When you order a new car (create an object), the robot makes sure the car does not leave the factory empty – it immediately installs the chosen brand, engine, and color. Without a constructor, you would get a "raw" chassis, and then you would have to manually set each property individually in the code, which would take a huge amount of time and open the door to numerous errors.

EXAMPLE

[file:Basic Constructor]
<?php
class Car {
    public $brand;
    public $model;

// The constructor accepts parameters upon creation
    public function __construct($brand, $model) {
        $this->brand = $brand;
        $this->model = $model;
        echo "Object for $brand $model was successfully created!<br>";
    }

public function info() {
        return "Vehicle: {$this->brand} {$this->model}";
    }
}

// We pass the parameters inside the parentheses with "new"
$myCar = new Car("Toyota", "Yaris");
echo $myCar->info();
?>

[file:Constructor in Inheritance (parent)]
<?php
// Superclass with basic logic
class Vehicle {
    public $brand;

public function __construct($brand) {
        $this->brand = $brand;
    }
}

// Subclass that extends the parent constructor
class ElectricCar extends Vehicle {
    public $batteryCapacity;

public function __construct($brand, $capacity) {
        // Important: First we call the parent constructor!
        parent::__construct($brand);
        $this->batteryCapacity = $capacity;
    }

public function status() {
        return "Brand: {$this->brand}, Battery: {$this->batteryCapacity} kWh";
    }
}

$tesla = new ElectricCar("Tesla", 75);
echo $tesla->status();
?>

RESULT

The result will be displayed here...

What is Worth Remembering About Constructors?

When designing your classes, always consider the following four golden rules of constructor operation:

Method Name: In PHP, the constructor is always named __construct (with two underscores before the word).
Automatic Call: You never call it manually like regular methods; PHP triggers it entirely on its own when using the new keyword.
Data Preparation: It is the ideal place for setting initial values, filling mandatory properties, and even for initial connections to a database.
Safety in Inheritance: If a subclass defines its own constructor, the parent constructor will not execute automatically. If you want to preserve the parent's logic, you must use the parent::__construct() command.