. PHP Design Patterns . PHP Design Patterns Bridge

PHP Design Patterns Bridge

About the Bridge

In the Bridge Design Pattern, functionality abstraction and implementation are in separate class hierarchies.

In this example we have BridgeBook which uses either BridgeBookCapsImp or BridgeBookStarsImp. BridgeBook will assign one implementation or the other each time BridgeBook is instantiated.

The bridge pattern is helpful when you want to decouple a class from it's implementation.

BridgeBook.php


//copyright Lawrence Truett and FluffyCat.com 2006, all rights reserved
  
  include_once('BridgeBookCapsImp.php');
  include_once('BridgeBookStarsImp.php');  
  
  abstract class BridgeBook {
      
    private $bbAuthor;
    private $bbTitle;
    private $bbImp;
    
    function __construct($author_in, $title_in, $choice_in) {
      $this->bbAuthor = $author_in;
      $this->bbTitle  = $title_in;
      if ('STARS' == $choice_in) {
        $this->bbImp = new BridgeBookStarsImp();
      } else {
        $this->bbImp = new BridgeBookCapsImp();
      }
    }    
  
    function showAuthor() {
      return $this->bbImp->showAuthor($this->bbAuthor);
    }
    
    function showTitle() {
      return $this->bbImp->showTitle($this->bbTitle);
    }
  
  }

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BridgeBookAuthorTitle.php

  
//copyright Lawrence Truett and FluffyCat.com 2006, all rights reserved
  
  include_once('BridgeBook.php');;  
  
  class BridgeBookAuthorTitle extends BridgeBook {    
  
    function showAuthorTitle() {
      return $this->showAuthor() . "'s " . $this->showTitle();
    }
  
  }

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BridgeBookTitleAuthor.php

//copyright Lawrence Truett and FluffyCat.com 2006, all rights reserved
  
  include_once('BridgeBook.php');;  
  
  class BridgeBookTitleAuthor extends BridgeBook {    
  
    function showTitleAuthor() {
      return $this->showTitle() . ' by ' . $this->showAuthor();
    }
  
  }

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BridgeBookImp.php


//copyright Lawrence Truett and FluffyCat.com 2006, all rights reserved 
  
  abstract class BridgeBookImp {    
  
    abstract function showAuthor($author);
    
    abstract function showTitle($title);

  }

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BridgeBookCapsImp.php


//copyright Lawrence Truett and FluffyCat.com 2006, all rights reserved 
  
  include_once('BridgeBookImp.php');  
  
  class BridgeBookCapsImp extends BridgeBookImp {    
  
    function showAuthor($author_in) {
      return strtoupper($author_in); 
    }
    
    function showTitle($title_in) {
      return strtoupper($title_in); 
    }
    
  }

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BridgeBookStarsImp.php


//copyright Lawrence Truett and FluffyCat.com 2006, all rights reserved 
  
  include_once('BridgeBookImp.php');  
  
  class BridgeBookStarsImp extends BridgeBookImp {    
  
    function showAuthor($author_in) {
      return Str_replace(" ","*",$author_in); 
    }
    
    function showTitle($title_in) {
      return Str_replace(" ","*",$title_in); 
    }
    
  }

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testBridge.php


//copyright Lawrence Truett and FluffyCat.com 2006, all rights reserved

  include_once('BridgeBookAuthorTitle.php');
  include_once('BridgeBookTitleAuthor.php');

  define('BR', '<'.'BR'.'>');

  echo 'BEGIN TESTING BRIDGE PATTERN'.BR;
  echo BR;
  
  echo 'test 1 - author title with caps'.BR;
  $book = 
    new BridgeBookAuthorTitle('Larry Truett','PHP for Cats','CAPS');
  echo $book->showAuthorTitle();
  echo BR.BR;

  echo 'test 2 - author title with stars'.BR;
  $book = 
    new BridgeBookAuthorTitle('Larry Truett','PHP for Cats','STARS');
  echo $book->showAuthorTitle();
  echo BR.BR;

  echo 'test 3 - title author with caps'.BR;
  $book = 
    new BridgeBookTitleAuthor('Larry Truett','PHP for Cats','CAPS');
  echo $book->showTitleAuthor();
  echo BR.BR;

  echo 'test 4 - title author with stars'.BR;
  $book = 
    new BridgeBookTitleAuthor('Larry Truett','PHP for Cats','STARS');
  echo $book->showTitleAuthor();
  echo BR.BR;

  echo 'END TESTING BRIDGE PATTERN'.BR;

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output of testBridge.php

BEGIN TESTING BRIDGE PATTERN


test 1 - author title with caps
LARRY TRUETT's PHP FOR CATS


test 2 - author title with stars
Larry*Truett's PHP*for*Cats


test 3 - title author with caps
PHP FOR CATS by LARRY TRUETT


test 4 - title author with stars
PHP*for*Cats by Larry*Truett


END TESTING BRIDGE 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

Comments Comments are left by visitors to FluffyCat.com, are not endorsed by FluffyCat.com, and may or may not be accurate.

Comment by mamad876 Rate this Comment

Hi,

I'm just thinking that your example is likely to be Strategy pattern instead of Bridge pattern.

Comment by Larry Rate this Comment

As noted in GOF p. 161, The Bridge Pattern and the Adapter Pattern are similar in that they both fill the need to allow unrelated classes to work together.

One essential difference is that in the Bridge Pattern the classes are designed to work together and are aware of each other's existence.

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