. PHP Design Patterns

PHP Design Patterns Decorator

About the Decorator

In the Decorator pattern, a class will add functionality to another class, without changing the other classes' structure.

In this example, the Book class will have it's title shown in different ways by the BookTitleDecorator and it's child classes BookTitleExclaimDecorator and BookTitleStarDecorator.

In my example I do this by having BookTitleDecorator make a copy of Book's title value, which is then changed for display. Depending on the implementation, it might be better to actually change the original object.

Book.php

//copyright Lawrence Truett and FluffyCat.com 2005, all rights reserved
  
  class Book {


    private $author;
    private $title;


    function __construct($title_in, $author_in) {
      $this->author = $author_in;
      $this->title  = $title_in;
    }


    function getAuthor() {return $this->author;}


    function getTitle() {return $this->title;}


    function getAuthorAndTitle() {
      return $this->getTitle() . ' by ' . $this->getAuthor();
    }


  }

download source, use right-click and "Save Target As..." to save with a .php extension.

BookTitleDecorator.php

//copyright Lawrence Truett and FluffyCat.com 2005, all rights reserved


  include_once('Book.php');


    class BookTitleDecorator {
	
    protected $book;
	protected $title;
	
    public function __construct(Book $book_in) {
	  $this->book = $book_in;
      $this->resetTitle();
    }
	
    //doing this so original object is not altered
	function resetTitle() {
	  $this->title = $this->book->getTitle();
	}


    function showTitle() {
	  return $this->title;
	}


  }

download source, use right-click and "Save Target As..." to save with a .php extension.

BookTitleExclaimDecorator.php

  include_once('BookTitleDecorator.php');
  
  class BookTitleExclaimDecorator extends BookTitleDecorator {
	
	   private $btd;


    public function __construct(BookTitleDecorator $btd_in) {
	     $this->btd = $btd_in;
    }


    function exclaimTitle() {
	     $this->btd->title = "!" . $this->btd->title . "!";
	   }


  }

download source, use right-click and "Save Target As..." to save with a .php extension.

BookTitleStarDecorator.php

  include_once('BookTitleDecorator.php');
  
    class BookTitleStarDecorator extends BookTitleDecorator {
	
	private $btd;


    public function __construct(BookTitleDecorator $btd_in) {
	  $this->btd = $btd_in;
    }


    function starTitle() {
	  $this->btd->title = Str_replace(" ","*",$this->btd->title);
	}


  }

download source, use right-click and "Save Target As..." to save with a .php extension.

Try the Design Patterns Video Tutorial from SourceMaking

testDecorator.php

//copyright Lawrence Truett and FluffyCat.com 2005, all rights reserved


  include_once('Book.php');
  include_once('BookTitleDecorator.php');
  include_once('BookTitleExclaimDecorator.php');
  include_once('BookTitleStarDecorator.php');


  echo tagins("html");
  echo tagins("head");  
  echo tagins("/head");  
  echo tagins("body");


  echo "BEGIN TESTING DECORATOR PATTERN";
  echo tagins("br").tagins("br");


  $patternBook = 
    new Book("Gamma, Helm, Johnson, and Vlissides",
	            "Design Patterns");
				
  $decorator = new BookTitleDecorator($patternBook);
  $starDecorator = new BookTitleStarDecorator($decorator);
  $exclaimDecorator = new BookTitleExclaimDecorator($decorator);
  
  echo "showing title : "
    .tagins("br");
  echo $decorator->showTitle();
  echo tagins("br").tagins("br");
  
  echo "showing title after two exclaims added : "
    .tagins("br");
  $exclaimDecorator->exclaimTitle();
  $exclaimDecorator->exclaimTitle();
  echo $decorator->showTitle();
  echo tagins("br").tagins("br");
  
  echo "showing title after star added : "
    .tagins("br");
  $starDecorator->starTitle();
  echo $decorator->showTitle();
  echo tagins("br").tagins("br");
  
  echo "showing title after reset: "
    .tagins("br");
  echo $decorator->resetTitle();
  echo $decorator->showTitle();
  echo tagins("br").tagins("br");


  echo tagins("br");
  echo "END TESTING DECORATOR PATTERN";
  echo tagins("br");
  
  echo tagins("/body");
  echo tagins("/html");
  
  //doing this so code can be displayed without breaks
  function tagins($stuffing) {
    return "<".$stuffing.">";
  }

download source, use right-click and "Save Target As..." to save with a .php extension.

output of testDecorator.php

BEGIN TESTING DECORATOR PATTERN


showing title : 
Design Patterns


showing title after two exclaims added : 
!!Design Patterns!!


showing title after star added : 
!!Design*Patterns!!


showing title after reset: 
Design Patterns



END TESTING DECORATOR PATTERN

References

Design Patterns
Design Patterns by Erich Gamma, Richard Helm, Ralph Johnson, and John Vlissides

PHP 5
The Official PHP web site
Core PHP Programming, 3rd Edition by Leon Atkinson and Zeev Suraski

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