OOP Basics: Objects

If classes are merely blueprints on paper, objects are the real, tangible things we build from those blueprints. In programming terminology, an object is also called an instance or a specimen of a class. The process of moving from theory (a class) into practice and creating a live thing in the computer's memory is called instantiation.

Imagine the following real-world examples:

Cookie Cutter (Class) determines the star shape. Baked Cookies (Objects) are the ones we can actually eat. Every cookie is made from the same cutter, but each can have a different topping or glaze (different property values).
Architectural Blueprint (Class) describes where the walls and windows stand. A Brick House (Object) is the actual one you can move into. You can build a whole neighborhood of identical houses from a single blueprint, but each will have its own house number and facade color.

EXAMPLE

[file:Cookie Cutter]
<?php
// CLASS: The blueprint that defines what a cookie has
class CookieCutter {
    public $shape = "Star"; // Default shape for everyone
    public $topping; // Specific property for each object

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

public function describeCookie() {
        return "A cookie in the shape of {$this->shape} has a great topping: {$this->topping}.<br>";
    }
}

// OBJECTS: We bake 3 completely different cookies from a single cutter!
$cookie1 = new CookieCutter("Chocolate");
$cookie2 = new CookieCutter("Icing sugar");
$cookie3 = new CookieCutter("Strawberry jam");

// We print their descriptions
echo $cookie1->describeCookie();
echo $cookie2->describeCookie();
echo $cookie3->describeCookie();
?>

[file:Class Definition]
<?php
// Here we only define the "blueprint"
class Person {
    public $firstName;
    public $lastName;

public function __construct($firstName, $lastName) {
        $this->firstName = $firstName;
        $this->lastName = $lastName;
    }
}
echo "The Person class is defined. There are no objects in memory yet.";
?>

[file:Creating an Object]
<?php
class Person {
    public $firstName;
    public $lastName;
    public function __construct($firstName, $lastName) {
        $this->firstName = $firstName;
        $this->lastName = $lastName;
    }
}

// We use the "new" keyword to create an object from the class
$person = new Person("yourFirstName", "yourLastName");

echo "Created object for: " . $person->firstName . " " . $person->lastName;
?>

[file:Complete Example]
<?php
class Person {
    public $firstName;
    public $lastName;

public function __construct($firstName, $lastName) {
        $this->firstName = $firstName;
        $this->lastName = $lastName;
    }

public function greet() {
        return "Hello, " . $this->firstName . " " . $this->lastName . "!";
    }
}

// Creation and usage
$person = new Person("yourFirstName", "yourLastName");
echo $person->greet();
?>

RESULT

The result will be displayed here...

How Do Objects Work Behind the Scenes?

When you use the new keyword in PHP, something magical happens: the computer reserves a special space in its working memory (RAM) exclusively for this new object. Every object you create from the same class is completely independent of the others.

If you change the color or mileage of your car (object), it won't affect your neighbor's car at all, even though both were made according to the same factory blueprint (class). Through objects, we manage data in our application in a safe and organized manner.