Introduction to Object Oriented Programming

For 2023 (and 2024 ...) - we are now fully retired from IT training.
We have made many, many friends over 25 years of teaching about Python, Tcl, Perl, PHP, Lua, Java, C and C++ - and MySQL, Linux and Solaris/SunOS too. Our training notes are now very much out of date, but due to upward compatability most of our examples remain operational and even relevant ad you are welcome to make us if them "as seen" and at your own risk.

Lisa and I (Graham) now live in what was our training centre in Melksham - happy to meet with former delegates here - but do check ahead before coming round. We are far from inactive - rather, enjoying the times that we are retired but still healthy enough in mind and body to be active!

I am also active in many other area and still look after a lot of web sites - you can find an index ((here))

So what exactly IS object oriented programming? Easy question to ask, but a hard one to answer in just a sentence or two. Let's try.

In an object oriented scenario, you group together all the pieces of code that relate to a certain type of data. That code grouping will be called a class and it will usually be kept in a separate file to your main programs, so that you can write a whole suite of programs that handle the same data in different ways without having to keep re-writing the low level code.

For example, this Blog might be using an "entry" class (a class is the name given to the bundle of code that relates to a type of data) so that the logic I use when I write each day is shared with the logic used to generate the pages you see when you read it on our site, and is also shared with the logic that's use if anyone calls up an XML feed.

This isn't an easy way to start writing a small and simple program, but it's great when you expand your applications. You don't have to re-invent the wheel ... and if you change the internals of a class, all your applications will just keep on running provided that you keep the calls to the class compatible with the previous ones. In other words, it's a great way of cutting maintenance costs too.

A language is described as "An object oriented language" if it has a number of extra features that weren't in languages such as Fortran, Algol and C (on which I cut my teeth) and which facilitate programming in the OO way. OO has its whole world of extra concepts and buzzwords, but to bring them all up here on a horse's mouth entry would take me beyond my challenge of telling you what OO is about in just a short item. Longer articles (part of our training notes) may be downloaded from our training notes site.
(written 2005-11-27, updated 2006-06-05)

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

Q907 - Object Orientation and General technical topics - Object Orientation: Design Techniques
  [80] OO - real benefits - (2004-10-09)
  [236] Tapping in on resources - (2005-03-05)
  [534] Design - one name, one action - (2005-12-19)
  [656] Think about your design even if you don't use full UML - (2006-03-24)
  [747] The Fag Packet Design Methodology - (2006-06-06)
  [831] Comparison of Object Oriented Philosophy - Python, Java, C++, Perl - (2006-08-13)
  [836] Build on what you already have with OO - (2006-08-17)
  [1047] Maintainable code - some positive advice - (2007-01-21)
  [1217] What are factory and singleton classes? - (2007-06-04)
  [1224] Object Relation Mapping (ORM) - (2007-06-09)
  [1435] Object Oriented Programming in Perl - Course - (2007-11-18)
  [1528] Object Oriented Tcl - (2008-02-02)
  [1538] Teaching Object Oriented Java with Students and Ice Cream - (2008-02-12)
  [2169] When should I use OO techniques? - (2009-05-11)
  [2170] Designing a heirarcy of classes - getting inheritance right - (2009-05-11)
  [2327] Planning! - (2009-08-08)
  [2380] Object Oriented programming - a practical design example - (2009-08-27)
  [2501] Simples - (2009-11-12)
  [2523] Plan your application before you start - (2009-12-02)
  [2717] The Multiple Inheritance Conundrum, interfaces and mixins - (2010-04-11)
  [2741] What is a factory? - (2010-04-26)
  [2747] Containment, Associative Objects, Inheritance, packages and modules - (2010-04-30)
  [2785] The Light bulb moment when people see how Object Orientation works in real use - (2010-05-28)
  [2865] Relationships between Java classes - inheritance, packaging and others - (2010-07-10)
  [2878] Program for reliability and efficiency - do not duplicate, but rather share and re-use - (2010-07-19)
  [2889] Should Python classes each be in their own file? - (2010-07-27)
  [2953] Turning an exercise into the real thing with extreme programming - (2010-09-11)
  [2977] What is a factory method and why use one? - Example in Ruby - (2010-09-30)
  [3063] Comments in and on Perl - a case for extreme OO programming - (2010-11-21)
  [3085] Object Oriented Programming for Structured Programmers - conversion training - (2010-12-14)
  [3260] Ruby - a training example that puts many language elements together to demonstrate the whole - (2011-04-23)
  [3454] Your PHP website - how to factor and refactor to reduce growing pains - (2011-09-24)
  [3607] Designing your application - using UML techniques - (2012-02-11)
  [3760] Why you should use objects even for short data manipulation programs in Ruby - (2012-06-10)
  [3763] Spike solutions and refactoring - a Python example - (2012-06-13)
  [3798] When you should use Object Orientation even in a short program - Python example - (2012-07-06)
  [3844] Rooms ready for guests - each time, every time, thanks to good system design - (2012-08-20)
  [3878] From Structured to Object Oriented Programming. - (2012-10-02)
  [3887] Inheritance, Composition and Associated objects - when to use which - Python example - (2012-10-10)
  [3928] Storing your intermediate data - what format should you you choose? - (2012-11-20)
  [3978] Teaching OO - how to avoid lots of window switching early on - (2013-01-17)
  [4098] Using object orientation for non-physical objects - (2013-05-22)
  [4374] Test driven development, and class design, from first principles (using C++) - (2014-12-30)
  [4430] The spirit of Java - delegating to classes - (2015-02-18)
  [4449] Spike solution, refactoring into encapsulated object methods - good design practise - (2015-03-05)
  [4628] Associative objects - one object within another. - (2016-01-20)

Q906 - Object Orientation and General technical topics - Object Orientation: Individual Objects
  [227] Bellringing and Programming and Objects and Perl - (2005-02-25)
  [1543] Learning Object Oriented Principles (and perhaps Java) - (2008-02-17)
  [1864] Object Oriented Perl - First Steps - (2008-11-01)
  [1925] Introduction to Object Oriented Programming - (2008-12-06)
  [2171] Cleaning up redundant objects - (2009-05-11)
  [2173] Basic OO principles - (2009-05-11)
  [2393] A first demonstration of OO, including polymorphism - (2009-09-04)
  [2651] Calculation within objects - early, last minute, or cached? - (2010-02-26)
  [3436] Moving from scripting to Object Orientation in Python - (2011-09-13)
  [3721] Naming blocks of code, structures and Object Orientation - efficient coding in manageable chunks - (2012-05-06)
  [4021] Spike solution, refactored and reusable, Python - Example - (2013-02-28)
  [4448] What is the difference between a function and a method? - (2015-03-04)
  [4591] From single block to structure and object oriented programming - (2015-12-02)
  [4650] Why populate object with values as you construct them? - (2016-02-18)

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