The problem: code duplication

Let's start with the following two classes that can generate an eBook and a paper book.

// Class to generate paperback books.
class Paperback {
  private $title   = "";
  private $content = "";
    
  function setTitle( $str )
  {
    $this->title = $str;
  }
    
  function setContent( $str )
  {
    $this->content = $str;
  }
    
  function printBook()
  {
    var_dump("The book '{$this->title}' was printed.");
  }
}

// Class to generate eBooks.
class Ebook {
  private $title   = "";
  private $content = "";
    
  function setTitle( $str )
  {
    $this->title = $str;
  }
    
  function setContent( $str )
  {
    $this->content = $str;
  }
    
  function generatePdf()
  {
    var_dump("A PDF was generated for the eBook '{$this->title}'.");
  }
}

You are probably concerned with the code duplication since both classes contain the private variables $title and $content as well as the methods that set them, setTitle and setContent.

The solution: abstract class

The template pattern suggests that we avoid the code duplication by creating an abstract class that the classes need to extend. Within this abstract class we convene the code instead of duplicating it. Since the subclasses inherit the code of the abstract class they are able to re-use the methods of the parent class, instead of each sub class having to duplicate the exact same code.

Let's create an abstact Book class and make it convene the duplicated code of the original classes. Be sure to make the variables protected so they can be accisble from the subclasses.

// The abstract parent class.
abstract class Book {
  protected $title;
  protected $content;
     
  function setTitle( $str )
  {
    $this->title = $str;
  }
    
  function setContent( $str )
  {
    $this->content = $str;
  }
}
 
class Paperback extends Book {
      
  function printBook()
  {
    var_dump("The book '{$this->title}' was printed.");
  }
}
 
class Ebook extends Book {
      
  function generatePdf()
  {
    var_dump("A PDF was generated for the eBook '{$this->title}'.");
  }
}

Let's test the code:

$paperback = new Paperback;
    
$paperback -> setTitle("The greatest paperback ever");
$paperback -> printBook();

And the result is:

string "The book 'The greatest paperback ever' was printed." (length=51)

In conclusion

As I said, the template pattern is the simplest design pattern ever. All we need to do is to convene the duplicated code from the classes into an abstract parent class and make the original classes into subclasses that inherit the code of the parent abstract class.

Was this tutorial helpful?

If so, the eBook"The essentials of object oriented PHP" can further help you.

"The essentials..." is an in-depth guide to help you quickly and easily increase your productivity and become a hot commodity in the job market.

Don't waste time!
Click on the green button to buy the eBook and start achieving your potential today!

Buy the eBook!