[thelist] Object Oriented Programming

David Kaufman david at gigawatt.com
Thu Jun 2 08:23:10 CDT 2011

Hi Kevin,

Despite the oft-cited "pillars", the best explanation I've ever heard of 
OO was (not coincidentally) the simplest.  I think it was in the second 
paragraph of a text book and it was the person/employee classes example 
which you've probably seen as well, where the developer codes a Person 
class to instantiate Person objects with attributes like first_name, 
last_name, date_of_birth, etc. and methods general to all people like 
age(), and can then reuse that code by inheriting from Person to create 
an Employee class, by simply adding employee-specific attributes and 
methods such as salary, department and, of course, terminate().

When future needs arise, such as the need to treat hourly and salaried 
Employees differently, it is easy to create classes for those, by 
further subclassing Employee.  The HourlyEmployee class might only need 
to contain one method that overrides, say, compute_paycheck() 
implemented one way, while SalariedEmployee has the same method 
implemented a different way.

To me the example illustrates the (alleged) benefits of OO Abstraction, 
Encapsulation and Inheritance much better than the definitions of those 
concepts do, and may do so in fewer syllables!  Bu then, for me, 
information is like code: less is more :-)

I will add that: I do wish I'd been taught in school that, while this 
type of class inheritance was *designed* to ease development and 
maintenance of code with oodles of opportunities for code reuse, in the 
real world it seldom works out that way.  In my experience, the class 
stack itself tends to add more complexity, inefficiency, and plain old 
bugs than the developer would have had to contended with, had she just 
reused code in other (non-hierarchical) ways.


On 5/30/2011 6:17 PM, Kipper Timmins wrote:
 > Hi all,
 > I was wondering if any of you could offer your opinion with regards
 > to what Object Oriented Programming actually is. Most developers
 > will know how to use it, however it seems defining it is full of a
 > lot of different opinions.
 > My current take on the foundations of OO (before we move further
 > into the topic) is the following:
 > 4 key pillars/concepts
 > Encapsulation : The ability to logically group functionality
 > together into a meaningful concept (object) without defining access
 > rights to the information.
 > Abstraction : The ability to remove irrelevant information for the
 > task at hand. i.e. a bank not holding records of your favourite
 > colour on your account records because the information has no
 > purpose there.
 > Inheritance : The ability to generalise concepts to improve
 > reusability.
 > Polymorphism : Early binding – Same method name with different
 > argument signature (usually within the same class). Late binding –
 > Same method name, same argument signature, different functionality
 > (between inherited classes)
 > I would really appreciate any of you sharing your thoughts on this.
 > Many thanks,
 > Kevin Timmins

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