Factory Class

PHP
1

I think I understand what a factory class does, I’m just unsure when I’d use it. For example, I have this is my bootstrap:

/**
 * Generic objects
 */								
$clean	 			= new Helpers\\Clean();
$page 				= new Helpers\\Page();
$email 				= new Helpers\\Email();
$date 				= new Helpers\\Date();
$seconds 			= new Helpers\\Seconds();
$image	 			= new Files\\Image();


/**
 * Database connection
 */
if($settings['DEV']) {

	$db = new Database\\Connection($settings['DEV_DATABASE_HOST'],
						          $settings['DEV_DATABASE'],
						          $settings['DEV_DATABASE_USER'],
						          $settings['DEV_DATABASE_PASSWORD'],
						          $settings['DEV_DATABASE_CHARSET'],
						          $settings['DEV_DATABASE_LOG']);
				
}
else {

	$db = new Database\\Connection($settings['LIVE_DATABASE_HOST'],
						          $settings['LIVE_DATABASE'],
						          $settings['LIVE_DATABASE_USER'],
						          $settings['LIVE_DATABASE_PASSWORD'],
						          $settings['LIVE_DATABASE_CHARSET'],
						          $settings['LIVE_DATABASE_LOG']);

}


/**
 * Objects that require dependencies
 */
$generate 			= new Helpers\\Generate($clean);
$format 			= new Helpers\\Format($clean);
$validateServer		= new Helpers\\ValidateServer($clean, $date);
$validateClient		= new Helpers\\ValidateClient($clean);
$generate			= new Helpers\\Generate($clean);
$query 				= new Database\\Query($db, $clean);
$file	 			= new Files\\File($clean);
$upload	 			= new Files\\Upload($file, $generate);
$search				= new Content\\Search($db, $clean);

If I understand factory classes they create a bunch of objects. But why not just have code like the above?

Finally, I have just found out about ReflectionClass. Does this have any relevance to factory classes or is it just for debugging?

Thanks.

2

There could be a few reasons for using factories. One is when the exact class to instantiate can vary depending on runtime information. For example, let’s pretend you have a variety of “Clean” classes, such as HtmlClean, JavaScriptClean, and SqlClean (though, I would name these as a noun “Cleaner” rather than as a verb).

class HtmlCleaner
{
    public function clean($something)
    {}
}

class JavaScriptCleaner
{
    public function clean($something)
    {}
}

class SqlCleaner
{
    public function clean($something)
    {}
}

class CleanerFactory
{
    public function getCleaner($content)
    {
        if (/* some test */) {
            return new HtmlCleaner();
        } elseif (/* some test */) {
            return new JavaScriptCleaner();
        } elseif (/* some test */) {
            return new SqlCleaner();
        }
    }
}

$cleanerFactory = new CleanerFactory();

// the factory decides which class to instantiate
$cleaner = $cleanerFactory->getCleaner('<html>');

Another example from the wiki page… Pretend you have classes GifReader and JpegReader. Which should be instantiated depends on runtime information, on the kind of image you’re trying to read.

class ImageReaderFactory
{
    public function getImageReader($image)
    {
        if (/* some test */) {
            return new GifReader();
        } elseif (/* some test */) {
            return new JpegReader();
        }
    }
}