Mediator Design Pattern in PHP

An object passes all interaction between a number of other objects through itself.

In this example, BookMediator is notified by BookAuthorColleague or BookTitleColleague if they change to all upper case or all lower case. When either changes case, BookMediator calls the other to change it’s case to match.

<?php

class BookMediator {
    private $authorObject;
    private $titleObject;
    function __construct($author_in, $title_in) {
      $this->authorObject = new BookAuthorColleague($author_in,$this);
      $this->titleObject  = new BookTitleColleague($title_in,$this);
    }
    function getAuthor() {return $this->authorObject;}
    function getTitle() {return $this->titleObject;}
    // when title or author change case, this makes sure the other
    // stays in sync
    function change(BookColleague $changingClassIn) {
      if ($changingClassIn instanceof BookAuthorColleague) {
        if ('upper' == $changingClassIn->getState()) {
          if ('upper' != $this->getTitle()->getState()) {
            $this->getTitle()->setTitleUpperCase();
          }
        } elseif ('lower' == $changingClassIn->getState()) {
          if ('lower' != $this->getTitle()->getState()) {
            $this->getTitle()->setTitleLowerCase();
          }
        }
      } elseif ($changingClassIn instanceof BookTitleColleague) {
        if ('upper' == $changingClassIn->getState()) {
          if ('upper' != $this->getAuthor()->getState()) {
            $this->getAuthor()->setAuthorUpperCase();
          }
        } elseif ('lower' == $changingClassIn->getState()) {
          if ('lower' != $this->getAuthor()->getState()) {
            $this->getAuthor()->setAuthorLowerCase();
          }
        }
      }
    }
}

abstract class BookColleague {
    private $mediator;
    function __construct($mediator_in) {
        $this->mediator = $mediator_in;
    }
    function getMediator() {return $this->mediator;}
    function changed($changingClassIn) {
        getMediator()->titleChanged($changingClassIn);
    }
}

class BookAuthorColleague extends BookColleague {
    private $author;
    private $state;
    function __construct($author_in, $mediator_in) {
      $this->author = $author_in;
      parent::__construct($mediator_in);
    }
    function getAuthor() {return $this->author;}
    function setAuthor($author_in) {$this->author = $author_in;}
    function getState() {return $this->state;}
    function setState($state_in) {$this->state = $state_in;}
    function setAuthorUpperCase() {
      $this->setAuthor(strtoupper($this->getAuthor()));
      $this->setState('upper');
      $this->getMediator()->change($this);
    }
    function setAuthorLowerCase() {
      $this->setAuthor(strtolower($this->getAuthor()));
      $this->setState('lower');
      $this->getMediator()->change($this);
    }
}

class BookTitleColleague extends BookColleague {
    private $title;
    private $state;
    function __construct($title_in, $mediator_in) {
        $this->title = $title_in;
        parent::__construct($mediator_in);
    }
    function getTitle() {return $this->title;}
    function setTitle($title_in) {$this->title = $title_in;}
    function getState() {return $this->state;}
    function setState($state_in) {$this->state = $state_in;}
    function setTitleUpperCase() {
        $this->setTitle(strtoupper($this->getTitle()));
        $this->setState('upper');
        $this->getMediator()->change($this);
    }
    function setTitleLowerCase() {
        $this->setTitle(strtolower($this->getTitle()));
        $this->setState('lower');
        $this->getMediator()->change($this);
    }
}
 
  writeln('BEGIN TESTING MEDIATOR PATTERN');
  writeln('');

  $mediator = new BookMediator('Gamma, Helm, Johnson, and Vlissides', 'Design Patterns');
 
  $author = $mediator->getAuthor();
  $title = $mediator->getTitle();
 
  writeln('Original Author and Title: ');
  writeln('author: ' . $author->getAuthor());
  writeln('title: ' . $title->getTitle());
  writeln('');
 
  $author->setAuthorLowerCase();
 
  writeln('After Author set to Lower Case: ');
  writeln('author: ' . $author->getAuthor());
  writeln('title: ' . $title->getTitle());
  writeln('');

  $title->setTitleUpperCase();
 
  writeln('After Title set to Upper Case: ');
  writeln('author: ' . $author->getAuthor());
  writeln('title: ' . $title->getTitle());
  writeln('');
 
  writeln('END TESTING MEDIATOR PATTERN');

  function writeln($line_in) {
    echo $line_in.'<br/>';
  }

?>

Output

BEGIN TESTING MEDIATOR PATTERN

Original Author and Title: 
author: Gamma, Helm, Johnson, and Vlissides
title: Design Patterns

After Author set to Lower Case: 
author: gamma, helm, johnson, and vlissides
title: design patterns

After Title set to Upper Case: 
author: GAMMA, HELM, JOHNSON, AND VLISSIDES
title: DESIGN PATTERNS

END TESTING MEDIATOR PATTERN

Code examples