Objects in PHP

 

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:

Syntax

To declare an object of a class we need to use new statement

class myclass

{

   ..

   ..

}

$obj=new myclass;

Example

<?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();
?>

Output:

Apple
Banana

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

Example

<?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();
?>

Output:

 

Name: Apple
Color: Red

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

<?php
class Fruit {
  public $name;
  function set_name($name) {
    $this->name = $name;
  }
}
$apple = new Fruit();
$apple->set_name("Apple");

echo $apple->name;
?>

Output:

Apple

2. Outside the class (by directly changing the property value):

Example

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

echo $apple->name;
?>

Output:

Apple

PHP - instanceof

You can use the instanceof keyword to check if an object belongs to a specific class:

Example

<?php
$apple = new Fruit();
var_dump($apple instanceof Fruit);
?>

Output:

bool(true)