What is a factory?

A Factory is somewhere that takes raw material, and converts into objects of some value. And so it is in Object Oriented Programming, where a "factory method" takes a chunk of raw material and makes an object out of it. It may differ from a constructor in that we may not know what type of object we're actually going to make when we call it!

Let's see an example (in PHP). Here's some source code which takes each of the lines from an incoming data file and passes them in turn into a factory method. The factory return an object each time it's called, which is stored into an array called options.

$southbound = file("southbound.txt");

$options = array();

foreach ($southbound as $lyne) {

   array_push($options,pubtrans::myfactory($lyne));

   }

From that application code, you can't tell what types of objects have been set up, nor can you tell how the code has decided which to set up - it's all encapsulated (hidden) within the factory.

Here's the code within the pubtrans class / namespace:

static function myfactory($lyne) {

  list($dep_t,$capa,$run_t,$dest,$wotsit) = explode(" ",trim($lyne));

  if ($wotsit == "train") {

    return (new train($dep_t,$capa,$run_t,$dest));

  } else {

    return (new bus($dep_t,$capa,$run_t,$dest));

  }

}

... and from that you can see that we're making either a train or a bus (they are probably classes that are subclasses of pubtrans, but not necessarily so).

The complete example is online - [source code] and [running example]. The data is [here].

(written 2010-04-26)

Associated topics are indexed as below, or enter http://melksh.am/nnnn for individual articles

H108 - Objects in PHP
  [4073] Learning about Object Orientation in PHP - a new set of examples - (2013-04-28)
  [4057] stdClass in PHP - using an object rather than an associative array - (2013-04-02)
  [3953] Objects in PHP - Revision - (2012-12-16)
  [3843] Caching Design Patterns - (2012-08-20)
  [3841] Copying, duplicating, cloning an object in PHP - (2012-08-18)
  [3840] Autoload in PHP - (2012-08-17)
  [3609] How do classes relate to each other? Associated Classes - (2012-02-12)
  [3608] Design Patterns - what are they? Why use them? - (2012-02-12)
  [3607] Designing your application - using UML techniques - (2012-02-11)
  [3211] Computer Graphics in PHP - World (incoming data) to Pixel (screen) conversion - (2011-03-24)
  [3210] Catchable fatal error in PHP ... How to catch, and alternative solutions such as JSON - (2011-03-22)
  [3142] Private and Public - and things between - (2011-01-22)
  [2922] Getting the OO design write - with PHP a example - (2010-08-14)
  [2921] Does copying a variable duplicate the contents? - (2010-08-14)
  [2774] PHP - Object Oriented Design in use - (2010-05-21)
  [2717] The Multiple Inheritance Conundrum, interfaces and mixins - (2010-04-11)
  [2680] Static class members in PHP - a documented example - (2010-03-16)
  [2641] Object Oriented Programming in PHP - (2010-02-19)
  [2632] Shipping a test harness with your class in PHP - (2010-02-12)
  [2435] Serialization - storing and reloading objects - (2009-10-04)
  [2434] Abstract classes, Interfaces, PHP and Java - (2009-10-03)
  [2380] Object Oriented programming - a practical design example - (2009-08-27)
  [2172] PHP4 v PHP5 - Object Model Difference - (2009-05-11)
  [2171] Cleaning up redundant objects - (2009-05-11)
  [2169] When should I use OO techniques? - (2009-05-11)
  [2160] PHP - getclass v instanceof - (2009-05-07)
  [1925] Introduction to Object Oriented Programming - (2008-12-06)
  [1820] Sorting objects in PHP - (2008-10-04)
  [1819] Calling base class constructors - (2008-10-03)
  [1682] Accounts in PHP - an OO demo - (2008-06-19)
  [1535] OO PHP demonstration - comparing objects and more - (2008-02-08)
  [1217] What are factory and singleton classes? - (2007-06-04)
  [1153] Object Oriented Model - a summary of changes from PHP4 to PHP5 - (2007-04-18)
  [1027] Cue the music, I'm happy. - (2007-01-09)
  [836] Build on what you already have with OO - (2006-08-17)
  [720] Planning a hotel refurb - an example of a Gant chart in PHP - (2006-05-14)
  [656] Think about your design even if you don't use full UML - (2006-03-24)
  [485] North, Norther and Northest - PHP 5 Objects - (2005-11-04)
  [421] Don't repeat code - use loops or functions - (2005-08-21)
  [343] Should I use structured or object oriented? - (2005-06-10)
  [205] PHP5 lets you say no - (2005-02-07)
  [124] PHP v Java - (2004-11-20)
  [67] Object Oriented Programming in PHP - (2004-09-29)

Q908 - Object Orientation and General technical topics - Object Orientation: Design Patterns
  [4098] Using object orientation for non-physical objects - (2013-05-22)
  [4096] Perl design patterns example - (2013-05-20)
  [4021] Spike solution, refactored and reusable, Python - Example - (2013-02-28)
  [3810] Reading files, and using factories to create vectors of objects from the data in C++ - (2012-07-21)
  [3716] Learning C++ - a design pattern for your first class - (2012-05-02)
  [2977] What is a factory method and why use one? - Example in Ruby - (2010-09-30)
  [2322] Looking for a practical standards course - (2009-08-05)
  [1224] Object Relation Mapping (ORM) - (2007-06-09)

Q907 - Object Orientation and General technical topics - Object Orientation: Design Techniques
  [3978] Teaching OO - how to avoid lots of window switching early on - (2013-01-17)
  [3928] Storing your intermediate data - what format should you you choose? - (2012-11-20)
  [3887] Inheritance, Composition and Associated objects - when to use which - Python example - (2012-10-10)
  [3878] From Structured to Object Oriented Programming. - (2012-10-02)
  [3844] Rooms ready for guests - each time, every time, thanks to good system design - (2012-08-20)
  [3798] When you should use Object Orientation even in a short program - Python example - (2012-07-06)
  [3763] Spike solutions and refactoring - a Python example - (2012-06-13)
  [3760] Why you should use objects even for short data manipulation programs in Ruby - (2012-06-10)
  [3454] Your PHP website - how to factor and refactor to reduce growing pains - (2011-09-24)
  [3260] Ruby - a training example that puts many language elements together to demonstrate the whole - (2011-04-23)
  [3085] Object Oriented Programming for Structured Programmers - conversion training - (2010-12-14)
  [3063] Comments in and on Perl - a case for extreme OO programming - (2010-11-21)
  [2953] Turning an exercise into the real thing with extreme programming - (2010-09-11)
  [2889] Should Python classes each be in their own file? - (2010-07-27)
  [2878] Program for reliability and efficiency - do not duplicate, but rather share and re-use - (2010-07-19)
  [2865] Relationships between Java classes - inheritance, packaging and others - (2010-07-10)
  [2785] The Light bulb moment when people see how Object Orientation works in real use - (2010-05-28)
  [2747] Containment, Associative Objects, Inheritance, packages and modules - (2010-04-30)
  [2523] Plan your application before you start - (2009-12-02)
  [2501] Simples - (2009-11-12)
  [2327] Planning! - (2009-08-08)
  [2170] Designing a heirarcy of classes - getting inheritance right - (2009-05-11)
  [1538] Teaching Object Oriented Java with Students and Ice Cream - (2008-02-12)
  [1528] Object Oriented Tcl - (2008-02-02)
  [1435] Object Oriented Programming in Perl - Course - (2007-11-18)
  [1047] Maintainable code - some positive advice - (2007-01-21)
  [831] Comparison of Object Oriented Philosophy - Python, Java, C++, Perl - (2006-08-13)
  [747] The Fag Packet Design Methodology - (2006-06-06)
  [534] Design - one name, one action - (2005-12-19)
  [507] Introduction to Object Oriented Programming - (2005-11-27)
  [236] Tapping in on resources - (2005-03-05)
  [80] OO - real benefits - (2004-10-09)

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