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Factory Method Design Pattern in PHP

In the Factory Method Pattern, a factory method defines what functions must be available in the non-abstract or concrete factory. These functions must be able to create objects that are extensions of a specific class. Which exact subclass is created will depend on the value of a parameter passed to the function.

In this example we have a factory method, AbstractFactoryMethod, that specifies the function, makePHPBook($param).

The concrete class OReillyFactoryMethod factory extends AbstractFactoryMethod, and can create the correct the extension of the AbstractPHPBook class for a given value of $param.

<?php

abstract class AbstractFactoryMethod {
    abstract function makePHPBook($param);
}

class OReillyFactoryMethod extends AbstractFactoryMethod {
    private $context = "OReilly";  
    function makePHPBook($param) {
	$book = NULL;	
        switch ($param) {
            case "us":
                $book = new OReillyPHPBook;
            break;
            case "other":
                $book = new SamsPHPBook;
            break;
            default:
                $book = new OReillyPHPBook;
            break;		  
        }  	  
	return $book;
    }
}

class SamsFactoryMethod extends AbstractFactoryMethod {
    private $context = "Sams";
    function makePHPBook($param) {
        $book = NULL;
        switch ($param) {
            case "us":
                $book = new SamsPHPBook;
            break;		
            case "other":
                $book = new OReillyPHPBook;
            break;
            case "otherother":
                $book = new VisualQuickstartPHPBook;
            break;
            default:
                $book = new SamsPHPBook;
            break;	  
        }	  
        return $book;
    }
}

abstract class AbstractBook {
    abstract function getAuthor();
    abstract function getTitle();
}

abstract class AbstractPHPBook {
    private $subject = "PHP";
}

class OReillyPHPBook extends AbstractPHPBook {
    private $author;
    private $title;
    private static $oddOrEven = 'odd';
    function __construct() {
        //alternate between 2 books
        if ('odd' == self::$oddOrEven) {
            $this->author = 'Rasmus Lerdorf and Kevin Tatroe';
            $this->title  = 'Programming PHP';
            self::$oddOrEven = 'even';
        } else {
            $this->author = 'David Sklar and Adam Trachtenberg';
            $this->title  = 'PHP Cookbook'; 
            self::$oddOrEven = 'odd';
        }  
    }
    function getAuthor() {return $this->author;}
    function getTitle() {return $this->title;}
}

class SamsPHPBook extends AbstractPHPBook {
    private $author;
    private $title;
    function __construct() {
        //alternate randomly between 2 books
        mt_srand((double)microtime()*10000000);
        $rand_num = mt_rand(0,1);      
 
        if (1 > $rand_num) {
            $this->author = 'George Schlossnagle';
            $this->title  = 'Advanced PHP Programming';
        } else {
            $this->author = 'Christian Wenz';
            $this->title  = 'PHP Phrasebook'; 
        }  
    }
    function getAuthor() {return $this->author;}
    function getTitle() {return $this->title;}
}

class VisualQuickstartPHPBook extends AbstractPHPBook {
    private $author;
    private $title;
    function __construct() {
      $this->author = 'Larry Ullman';
      $this->title  = 'PHP for the World Wide Web';
    }
    function getAuthor() {return $this->author;}
    function getTitle() {return $this->title;}
}

  writeln('START TESTING FACTORY METHOD PATTERN');
  writeln('');

  writeln('testing OReillyFactoryMethod');
  $factoryMethodInstance = new OReillyFactoryMethod;
  testFactoryMethod($factoryMethodInstance);
  writeln('');

  writeln('testing SamsFactoryMethod');
  $factoryMethodInstance = new SamsFactoryMethod;
  testFactoryMethod($factoryMethodInstance);
  writeln('');

  writeln('END TESTING FACTORY METHOD PATTERN');
  writeln('');

  function testFactoryMethod($factoryMethodInstance) {
    $phpUs = $factoryMethodInstance->makePHPBook("us");
    writeln('us php Author: '.$phpUs->getAuthor());
    writeln('us php Title: '.$phpUs->getTitle());

    $phpUs = $factoryMethodInstance->makePHPBook("other");
    writeln('other php Author: '.$phpUs->getAuthor());
    writeln('other php Title: '.$phpUs->getTitle());
 
    $phpUs = $factoryMethodInstance->makePHPBook("otherother");
    writeln('otherother php Author: '.$phpUs->getAuthor());
    writeln('otherother php Title: '.$phpUs->getTitle());
  }

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

Output

START TESTING FACTORY METHOD PATTERN

testing OReillyFactoryMethod
us php Author: Rasmus Lerdorf and Kevin Tatroe
us php Title: Programming PHP
other php Author: George Schlossnagle
other php Title: Advanced PHP Programming
otherother php Author: David Sklar and Adam Trachtenberg
otherother php Title: PHP Cookbook


testing SamsFactoryMethod
us php Author: Christian Wenz
us php Title: PHP Phrasebook
other php Author: Rasmus Lerdorf and Kevin Tatroe
other php Title: Programming PHP
otherother php Author: Larry Ullman
otherother php Title: PHP for the World Wide Web


END TESTING FACTORY METHOD PATTERN

Code examples

More info, diagrams and examples of the Factory Method design pattern you can find on our new resource Refactoring.Guru.