PHP Object Oriented Programming (OOPs) concept Tutorial with Example

Details

What is OOPs?

Object Oriented is an approach to software development that models application around real world objects such as employees, cars, bank accounts, etc. A class defines the properties and methods of a real world object. An object is an occurrence of a class.

The three basic components of object orientation are;

Object Oriented Programming Principles

The three major principles of OOP are;

OOPs Concepts in PHP

PHP is an object oriented scripting language; it supports all of the above principles. The above principles are achieved via;

Now that we have the basic knowledge of OOP and how it is supported in PHP, let us look at examples that implement the above principles

What is UML?

Unified Modeling Language UML is a technique used to design and document object oriented systems.

UML produces a number of documents, but we will look at the class diagram which is very important to object oriented php programming.

Class Diagram Example

PHP Object Oriented Programming (OOPs)

Class Diagram Key

How to Create a class in PHP

The class keyword is used to define a class in PHP. Below are the rules for creating a class in PHP.

Let’s say we want to create a class for representing animals.

We will start with identifying the features that are common to all animals.

The diagram below shows the diagram for the animal

PHP Object Oriented Programming (OOPs)

Let’s now code our animal class 

<?php
class Animal
{
    private $family;
    private $food;
    public function __construct($family, $food)
    {
        $this->family = $family;
        $this->food   = $food;
    }
    public function get_family()
    {
        return $this->family;
    }
    public function set_family($family)
    {
        $this->family = $family;
    }
    public function get_food()
    {
        return $this->food;
    }
    public function set_food($food)
    {
        $this->food = $food;
    }
}
?>

  HERE,

How implement Inheritance in PHP

We will work with a cow and a lion. Both the cow and lion inherit from the Animal class.

The class diagram below shows the relationships.

PHP Object Oriented Programming (OOPs)

Note the cow inherits from the animal class and defines its own variable and methods too.

Let’s now code the Cow class 

<?php
class Cow extends Animal
{
    private $owner;
    public function __construct($family, $food)
    {
        parent::__construct($family, $food);
    }
    public function set_owner($owner)
    {
        $this->owner = $owner;
    }
    public function get_owner()
    {
        return $this->owner;
    }
}
?>

  Let’s now code the Lion class 

<?php
class Lion extends Animal
{
    public function __construct($family, $food)
    {
        parent::__construct($family, $food);
    }
}
?>

  HERE,

How to Create object of the class

The Animal, Cow, and Lion classes should all be in the same directory for simplicity’s sake.

Let’s now create the application that uses our classes.

PHP Class Example 

<?php
require 'Animal.php';
require 'Cow.php';
require 'Lion.php';
$cow  = new Cow('Herbivore', 'Grass');
$lion = new Lion('Canirval', 'Meat');
echo '<b>Cow Object</b> <br>';
echo 'The Cow belongs to the ' . $cow->get_family() . ' family and eats ' . $cow->get_food() . '<br><br>';
echo '<b>Lion Object</b> <br>';
echo 'The Lion belongs to the ' . $lion->get_family() . ' family and eats ' . $lion->get_food();
?>

 

Testing our application

Let’s now view our application in a web browser

. PHP Object Oriented Programming (OOPs)

Fantastic right! Let’s now look at the third principle of OOP, polymorphism.

Let’s say we want to develop an application that connects to different database engines such as MySQL and SQL Server but use the same uniform interface.

We can create an interface that defines the standard methods and an abstract class that implements the common methods.

The class diagram below illustrates the relationship among our abstract class, interface, and implementation classes.

PHP Object Oriented Programming (OOPs)

Let’s now create our abstract class 

<?php
abstract class DBCommonMethods
{
    private $host;
    private $db;
    private $uid;
    private $password;
    public function __construct($host, $db, $uid, $password)
    {
        $this->host     = $host;
        $this->db       = $db;
        $this->uid      = $uid;
        $this->password = $password;
    }
}
?>

  HERE,

Let’s now create the interface that contains the standard methods which will be implemented differently depending on the database engine. 

<?php
interface DBInterface
{
    public function db_connect();
    public function insert($data);
    public function read($where);
    public function update($where);
    public function delete($where);
}
?>

  HERE,

Let’s now create the concrete classes that will extend the DBCommonMethods class and extend the DBInterface interface. MySQLDriver.php 

<?php class MySQLDriver extends 
DBCommonMethods implements DBInterface { public function __construct($host, $db, $uid, $password) 
{ 
parent::__construct($host, $db, $uid, $password); } 
public function db_connect() { //connect code goes here } 
public function delete($where) { //delete code goes here } 
public function insert($data) { //insert code goes here } 
public function read($where) { //read code goes here } 
public function update($where) { //update code goes here } 
} ?>

  MSSQLServerDriver.php 

<?php 
class MSSQLServerDriver extends 
DBCommonMethods implements DBInterface { public function __construct($host, $db, $uid, $password)
 { 
 parent::__construct($host, $db, $uid, $password); } 
 public function db_connect() { //connect code goes here } 
 public function delete($where) { //delete code goes here }
 public function insert($data) { //insert code goes here }
 public function read($where) { //read code goes here }
 public function update($where) { //update code goes here }
 } ?>

  HERE,

Usage of the above code The code using the above class would look like this 

<?php $db = new MySQLDriver($host,$db,$uid,$password); ?>

Or 

<?php $db = new MSSQLServerDriver ($host,$db,$uid,$password); ?>

The rest of the code would be the same for both drivers such as; 

<?php
$db->db_connect();
$db->insert($data);
?>

Summary

 

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