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7.2 PHP Classes/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

<?php
class Fruit {
  // code goes here...
}
?>

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:

Example 1: PHP Classes/Objects - Define a Class

<?php
class Fruit {
  // Properties
  public $name;
  public $color;

  // Methods
  function set_name($name) {
    $this->name = $name;
  }
  function get_name() {
    return $this->name;
  }
}
?>

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 is created using the new keyword.
In the example below, $apple and $banana are instances of the class Fruit:

Example 2: PHP Classes/Objects - Define Objects

<?php
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 "<br>";
echo $banana->get_name();
?>

In the example below, we add two more methods to class Fruit, for setting and getting the $color property:

Example 3: PHP Classes/Objects - Define Objects part 2

<?php
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 "<br>";
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

<?php
class Fruit {
  public $name;
}
$apple = new Fruit();
?>

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 4: PHP Classes/Objects - The $this Keyword part 1

<?php
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 5:PHP Classes/Objects - The $this Keyword part 2

<?php
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:

Example 6: PHP Classes/Objects - instanceof

<!DOCTYPE html>
<html>
<body>

<?php
class Fruit {
  // Properties
  public $name;
  public $color;

  // Methods
  function set_name($name) {
    $this->name = $name;
  }
  function get_name() {
    return $this->name;
  }
}

$apple = new Fruit();
var_dump($apple instanceof Fruit);
?>
 
</body>
</html>

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Example files created in this module:
PHP Classes/Objects - Define a Class PHP Classes/Objects - Define Objects part 1 PHP Classes/Objects - Define Objects part 2 PHP Classes/Objects - The $this Keyword part 1 PHP Classes/Objects - The $this Keyword part 2 PHP Classes/Objects - instanceof PHP Constructor part 1 PHP Constructor part 2 PHP Destructor part 1 PHP Destructor part 2 PHP Access Modifiers part 1 PHP Access Modifiers part 2 PHP Inheritance PHP Inheritance - Inheritance and the Protected Access Modifier part 1 PHP Inheritance - Inheritance and the Protected Access Modifier part 2 PHP Inheritance - Overriding Inherited Methods PHP Inheritance - The final Keyword part 1 PHP Inheritance - The final Keyword part 2 PHP Class Constants part 1 PHP Class Constants part 2 PHP Abstract Classes part 1 PHP Abstract Classes part 2 PHP Abstract Classes part 3 PHP Interfaces - Using Interfaces part 1 PHP Interfaces - Using Interfaces part 2 PHP - Using Traits PHP - Using Multiple Traits PHP Static Methods part 1 PHP Static Methods part 2 PHP Static Methods part 3 PHP Static Methods part 4 PHP Static Properties part 1 PHP Static Properties part 2 PHP Static Properties part 3 menu Test (text file for navigating the site) Drop Down Menu PHP Namespaces - Declaring a Namespace PHP Namespaces - Using Namespaces part 1 PHP Namespaces - Using Namespaces part 2 PHP Namespaces - Namespace Alias part 1 PHP Namespaces - Namespace Alias part 2 PHP Iterables - Using Iterables part 1 PHP Iterables - Using Iterables part 2 PHP Iterables - Creating Iterables