Introduction to OOP using PHP - Page 4

In the previous page we covered a lot of territory, and we will wrap things up on this page by covering the last topic, Inheritance.

Introducing Inheritance
To make this system more robust, we don't want all of the users in our group to have the same status. Some users need to be administrators, others moderators, and others just regular users. How can we account for this in our objects? The answer is inheritance - the ability for one class to inherit methods and properties from another class. First, let's take a look at inheritance in code:

/* Kirupa has admin powers */ $kirupa = new Admin( array( 'name' => 'Kirupa' ) ); echo $kirupa->getName().'<br />'; // Kirupa echo $kirupa->getAdmin(); // Administrator /* Regular does not have admin powers */ $regular = new User( array( 'name' => 'Regular' ) ); $regular->getAdmin(); // breaks our code /* Normal User class */ class User { private $name; function __construct( $attribs ) { $this->name = $attribs['name']; } function getName() { return $this->name; } } /* Admin is a User, but with additional functionality */ class Admin extends User { function getAdmin() { return 'Administrator'; } }

As you can see, our Admin object has inherited the functionality of the User class using the keyword extends. On top of that, our Admin is given some additional functionality. In this case, our User class is known as the superclass. In PHP, a class may only inherit one superclass. There are more nuances to inheritance, but this tutorial will only cover the basics. In a more realistic scenario, we would code more functionality for just administrators. Perhaps something like:

/* Additional functionality for just Administrators */ class Admin extends User { function banUser( $id ) { /* code to ban user */ } function unbanUser( $id ) { /* code to unban or activate user account */ } //... }

For the sake of time and focus, these methods haven't actually been coded. But this should give you some insight into how inheritance works and why it can be useful.

Continue on for a few parting words and direction.

Parting Words
By now, you should understand what objects, how to create them, and how to access their properties and methods. This tutorial is by no means all-encompassing. In fact, this is just the tip of the iceberg and was designed as such. For further reading, I suggest PHP5: Objects, Patterns, and Practice by Matt Zandstra. In addition, you could read through the OOP documentation provided at php.net.

As you begin to understand OOP more and your PHP code becomes more object oriented, you will find more code reusable and ultimately save time and energy. Pre-existing code resources such as PEAR and PHPClasses.org will become increasingly useful.

If you have questions related to this tutorial or PHP in general, post them in the Server-Side forum here at kirupa.com.

Brian Haveri aka bwh2 brianhaveri.com

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