A short series on OOP (Object Orient(at)ed Programming)

I'm going to do a short series of blog entries on OOP. I'll be using 2 languages in order to emphasise that the concepts are not language specific. All then entries will have simple code to demonstrate the point and be short in text.

Why OOP?

Good question Mick. Funnily enough, when you begin learning a language, it's rare to dive into OOP. It's possible that just grapsing this first concept would be enough to put any newbie off. Unfortunately, this also presents it's own problem. The newbie was doing perfectly well, creating useful code, only to be held up by a new concept (OOP) which slows them down. So the first question on their mind is why do I have to learn OOP? What is it going to give me.

Enough Mick. Give me the answer. Here I probably attack the problem from a different point of view than many of my programming friends.

Suppose I asked you to explain something. The mug of tea I'm drinking from. You might say, It's a cylindrical object, just big enough to hold, with a handle. It's yellow. They don't always look like that. Some are small for espresso, some are blue etc.

This would be an OOP way of looking at a mug of tea. Something which actually comes naturally to us. Strangely, if you were to use the concept we come into programming with (procedural), you'd describe the cup of tea as, 'It is the thing I am drinking from'.

First concept - classes and objects

So, here is the first concept. What is a class, and what is an object?
A class is a description of the thing. An object is a version of the thing.
Using our cup of tea example, we create a class called 'cup of tea', and in order to have a cup of tea, we need to create an object (my cup of tea).

Time to start coding I think. We are going to do this with 2 languages; PHP and JavaScript. First the classes.
PHP : cupoftea.class.php
<?php
class cupoftea
{
public $height, $diameter, $colour;
}
?>

JavaScript : cupoftea.class.js
cupoftea = function()
{
var height, diameter, colour;
};

Now a file (index.php) which creates objects from both.
<?php
require_once 'cupoftea.class.php';
$mycupoftea = new cupoftea;
$mycupoftea->height = 20;
echo $mycupoftea->height;
?>

<script src="cupoftea.class.js"></script>
<script>
var mycupoftea = new cupoftea;
mycupoftea.height = 30;
document.write(mycupoftea.height);
</script>