PHP OOP — Classes and Objects
A class is a template for objects, and an object is an instance of class.
OOP Case
Let’s assume we have a class named Fruit. A Fruit can have properties like name, color, weight, etc. We can define variables like $name, $color, and $weight to hold the values of these properties.
When the individual objects (apple, banana, etc.) are created, they inherit all the properties and behaviors from the class, but each object will have different values for the properties.
Define a Class
A class is defined by using the class keyword, followed by the name of the class and a pair of curly braces (<>). All its properties and methods go inside the braces:
Syntax
Below we declare a class named Fruit consisting of two properties ($name and $color) and two methods set_name() and get_name() for setting and getting the $name property:
class Fruit // Properties
public $name;
public $color;
// Methods
function set_name($name) $this->name = $name;
>
function get_name() return $this->name;
>
>
?>
Note: In a class, variables are called properties and functions are called methods!
Define Objects
Classes are nothing without objects! We can create multiple objects from a class. Each object has all the properties and methods defined in the class, but they will have different property values.
Objects of a class are created using the new keyword.
In the example below, $apple and $banana are instances of the class Fruit:
Example
class Fruit // Properties
public $name;
public $color;
// Methods
function set_name($name) $this->name = $name;
>
function get_name() return $this->name;
>
>
$apple = new Fruit();
$banana = new Fruit();
$apple->set_name(‘Apple’);
$banana->set_name(‘Banana’);
echo $apple->get_name();
echo «
«;
echo $banana->get_name();
?>
In the example below, we add two more methods to class Fruit, for setting and getting the $color property:
Example
class Fruit // Properties
public $name;
public $color;
// Methods
function set_name($name) $this->name = $name;
>
function get_name() return $this->name;
>
function set_color($color) $this->color = $color;
>
function get_color() return $this->color;
>
>
$apple = new Fruit();
$apple->set_name(‘Apple’);
$apple->set_color(‘Red’);
echo «Name: » . $apple->get_name();
echo «
«;
echo «Color: » . $apple->get_color();
?>
PHP — The $this Keyword
The $this keyword refers to the current object, and is only available inside methods.
Look at the following example:
Example
So, where can we change the value of the $name property? There are two ways:
1. Inside the class (by adding a set_name() method and use $this):
Example
class Fruit public $name;
function set_name($name) $this->name = $name;
>
>
$apple = new Fruit();
$apple->set_name(«Apple»);
2. Outside the class (by directly changing the property value):
Example
class Fruit public $name;
>
$apple = new Fruit();
$apple->name = «Apple»;
PHP — instanceof
You can use the instanceof keyword to check if an object belongs to a specific class: