What is a Factory Design Pattern? Explain with an example?

The Factory pattern allows for the instantiation of objects at runtime. It is called a Factory Pattern since it is responsible for "manufacturing" an object. A Parameterized Factory receives the name of the class to instantiate as argument.

Parameterized Factory Method


<?php
class Example
{
    // The parameterized factory method
    public static function factory($type)
    {
        if (include_once 'Drivers/' . $type . '.php') {
            $classname = 'Driver_' . $type;
            return new $classname;
        } else {
            throw new Exception('Driver not found');
        }
    }
}
?>

Defining this method in a class allows drivers to be loaded on the fly. If the Example class was a database abstraction class, loading a MySQL and SQLite driver could be done as follows:


<?php
// Load a MySQL Driver
$mysql = Example::factory('MySQL');

// Load an SQLite Driver
$sqlite = Example::factory('SQLite');
?>