php oop 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

<?phpclass 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

<?phpclass 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 is created using the new keyword.

In the example below, $apple and $banana are instances of the class Fruit:

Example

<?phpclass 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

<?phpclass 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

<?phpclass 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

<?phpclass 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

<?phpclass 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

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

Fruit);?>