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Using this class is simple — you start by referencing the

rss_factory.inc.php

file (which contains the

class), and creating your

$rss_feed

object:

<?php

// load the URL factory library

require_once ‘include/rss_factory.inc.php’;

// create feed

$rss_feed = new RSSFactory(‘SEOEgghead.com New Products Feed’,

http://www.seoegghead.com/seo-with-php-updates.html’,

‘Exciting new products, updated daily’);

Your class is named

RSSFactory

, and the object you create is named

$rss_feed

. You create the

object using the

new

operator, and, as you can see, you provide parameters in parentheses after the

class name.

Class? Object? An OOP Primer

The term

class

comes from the lexicon of object-oriented programming (OOP). If you

do not know much about OOP, here is a very quick primer that will help you under-

stand the

RSSFactory

, as well as other examples in this book that use this language

feature.

As the name implies, OOP puts objects at the center of the programming model. The

object

is the most important concept in the world of OOP — a self-contained entity that

has state and behavior, just like a real-world object.

A class acts as a blueprint for the object, and an object represents an instance of the

class defined by its state. You may have objects of class

Car

, for example, and create as

many

Car

objects as desired — named

$myCar

,

$johnsCar

,

$davesCar

, and so on.

But

$davesCar

may be stopped while John is busy outrunning a police officer on the

freeway at 100MPH.

So you get the idea; the class defines the

functionality

provided by the objects. All objects

of type Car will have the same basic capabilities — for example, the ability to accelerate

to a new speed. However, each individual Car object may register a different speed on

its speedometer at any particular time.

The object’s state is described by its variable fields, also called “properties.” Its func-

tionality is defined by its “methods.” These methods are functions inside a class, except

that they are called through (

->

) an object and reference the functions in the context of

the state provided by its properties.

In the particular example of the RSS Factory exercise, the class is named

RSSFactory

,

and the object you create is named

$rss_feed

. When you needed to call the

addItem

method of the

$rss_feed

object, you typed

$rss_feed->addItem

to add an item to

the object. You did this twice to add two feed items. Finally, to output the feed you

called

echo $rss_feed->get()

, which displays the feed in accordance with the

items that you added to it.

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Chapter 7: Web Feeds and Social Bookmarking

c07.qxd:c07 10:42 158

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