Building a few simple subclasses - PHP

If you're looking for a friendly guide on how to implement the template design pattern with PHP 5, then this group of articles might be what you need. Welcome to the final installment of the series that began with "Working with template classes in PHP 5." As the title indicates, this series steps you through creating template classes in PHP-controlled development environments, and also shows you how to use this rather uncommon pattern in real-world situations.

TABLE OF CONTENTS:

By: Alejandro Gervasio

Poor Best

Rating:

/ 2

March 26, 2007

print this article

SEARCH DEV SHED

TOOLS YOU CAN USE

As you'll certainly recall from the previous section, the template class that you saw presented a method called "getFormattedFileContents()," which doesn't have a concrete implementation. Naturally, this fact implies that the method in question must be explicitly defined by all the subclasses derived from the corresponding parent.

Therefore, I'm going to build three different child classes. These classes will be tasked with displaying the data fetched from a given file in diverse formats. With reference to this, the first class will return file contents as an uppercased string, while the other two will show this data in (X)HTML and XML formats respectively.

Having explained how these subclasses are going to work, you can now take a look at their respective signatures. They look like this:

// define concrete 'UppercasedFileTemplate' class
class UppercasedFileTemplate extends FileTemplate{
   public function getFileSize($fileProcessor){
     return 'SIZE OF DATA FILE IS :'.strtoupper($fileProcessor-
>getFileSize()).' BYTES';
   }
   public function getFormattedFileContents($fileProcessor){
     return 'CONTENTS OF DATA FILE ARE AS FOLLOWS :'.strtoupper
($fileProcessor->readData());
   }
}

// define concrete 'HTMLFileTemplate' class
class HTMLFileTemplate extends FileTemplate{
   public function getFileSize($fileProcessor){
     return '<html><head><title>Testing Template Pattern</title></head><body><h2>Size of data file is:
'.$fileProcessor->getFileSize().' bytes</h2>';
   }
   // display file contents as HTML
   public function getFormattedFileContents($fileProcessor){
     $output='<p>Contents of data file are as follows :</p>';
     $contents=explode("n",$fileProcessor->readData());
     foreach($contents as $line){
       $output.='<p>'.$line.'</p>';
     }
     $output.='</body></html>';
     return $output;
   }
}

// define concrete 'XMLFileTemplate' class
class XMLFileTemplate extends FileTemplate{
   public function getFileSize($fileProcessor){
     return '<?xml version="1.0" encoding="iso-8859-1"?><contents><size>Size of data file is: '.$fileProcessor-
>getFileSize().' bytes</size>';
   }
   // display file contents as XML
   public function getFormattedFileContents($fileProcessor){
     $output='';
     $contents=explode("n",$fileProcessor->readData());
     foreach($contents as $line){
       $output.='<data>'.$line.'</data>';
     }
     $output.='</contents>';
     return $output;
   }
}

As you'll possibly agree, the pertinent structures of the above three subclasses are quite simple to understand. As you can see, each one of them accepts an instance of the file processor class that was shown in a previous section, and implements concretely the "getFormattedFileContents()" method that you learned before.

Of course, the output format applied to the data retrieved from a specified file will depend on the subclass being instantiated, certainly a fact that can be seen clearly when examining each of the subclasses listed above.

Okay, now that you know how the previous child classes look, the programmatic schema imposed by the template pattern should be familiar to you, since on top of the hierarchy there's a template class that defines a specific formatting algorithm, which is implemented by the respective subclasses.

Nonetheless, I believe that the functionality of the template pattern is better appreciated by a functional example. In the upcoming section I'm going to build a simple PHP script where all the previous template classes will be put to work in conjunction.

Want to see how this script will be created? Keep reading, please.

Next: Seeing the template pattern in action >>