Constructor (__construct)

Part of the Object Oriented Programming section of Coddy's PHP journey — lesson 7 of 91.

The __construct method is a special method that automatically runs when you create a new object. It initializes the object's properties.

Here is an example of a class with a constructor:

<?php
class Dog {
    public $name;
    public $breed;

    public function __construct($name, $breed) {
        $this->name = $name;
        $this->breed = $breed;
    }
}

The __construct method takes parameters and assigns them to properties using $this.

Create objects using the constructor:

$rex = new Dog("Rex", "German Shepherd");
$buddy = new Dog("Buddy", "Golden Retriever");

When you call new Dog("Rex", "German Shepherd"), PHP automatically calls __construct and passes the arguments.

Access the properties that were set by the constructor:

echo $rex->name . "\n";
echo $rex->breed . "\n";
echo $buddy->name . "\n";
echo $buddy->breed . "\n";

Output:

Rex
German Shepherd
Buddy
Golden Retriever

You can also have a constructor with default parameter values:

class Cat {
    public $name;
    public $age;

    public function __construct($name, $age = 1) {
        $this->name = $name;
        $this->age = $age;
    }
}

$fluffy = new Cat("Fluffy", 3);
$whiskers = new Cat("Whiskers");  // age defaults to 1

echo $fluffy->name . " is " . $fluffy->age . " years old\n";
echo $whiskers->name . " is " . $whiskers->age . " years old\n";

Output:

Fluffy is 3 years old
Whiskers is 1 years old

Key Point: The __construct method ensures every object is properly set up with its initial data when created. It saves you from manually setting properties after object creation.

Challenge

Easy

You are given PHP files (book.php and driver.php) to implement a book system.

Your task is to:

Complete the Book class in book.php with a __construct method that initializes $title, $author, and $pages properties
In driver.php, import and create a book object for "Harry Potter" by "J.K. Rowling" with 400 pages

Follow the TODO comments in each file.

Cheat sheet

The __construct method is a special method that automatically runs when you create a new object to initialize its properties.

Define a constructor in a class:

<?php
class Dog {
    public $name;
    public $breed;

    public function __construct($name, $breed) {
        $this->name = $name;
        $this->breed = $breed;
    }
}

Create objects using the constructor:

$rex = new Dog("Rex", "German Shepherd");
$buddy = new Dog("Buddy", "Golden Retriever");

Access properties set by the constructor:

echo $rex->name;  // Rex
echo $rex->breed;  // German Shepherd

Constructors can have default parameter values:

class Cat {
    public $name;
    public $age;

    public function __construct($name, $age = 1) {
        $this->name = $name;
        $this->age = $age;
    }
}

$fluffy = new Cat("Fluffy", 3);
$whiskers = new Cat("Whiskers");  // age defaults to 1

Try it yourself

<?php
require_once 'book.php';

// TODO: Create a Book object with:
// title: "Harry Potter", author: "J.K. Rowling", pages: 400
$myBook = ?;

echo "'" . $myBook->title . "' by " . $myBook->author . ", " . $myBook->pages . " pages\n";

Test yourself

This lesson includes a short quiz. Start the lesson to answer it and track your progress.

Constructor (__construct)

Cheat sheet

All lessons in Object Oriented Programming