Classes and Objects

Classes and Objects

// The constructor function

function Page()

{

$this->page = '';

}

Within any method (including the constructor) $this points to the object in

which the method is running. It allows the method to access the other methods

and variables that belong to that particular object. The -> (arrow) operator that

follows $this is used to point at a property or method that's named within the

object.

In the example above, the constructor assigns an empty string value to the $page

member variable we declared at the start. The idea of the $this variable may

seem awkward and confusing to start with, but it's a common strategy employed

by other programming languages, such as Java[5], to allow class members to interact

with each other. You'll get used to it very quickly once you start writing

object oriented PHP code, as it will likely be required for almost every method

your class contains.

Of the other class methods, addHeader and addFooter are almost the same as

before; however, notice that they no longer return values. Instead, they update

the object's $page member variable, which, as you'll see, helps simplify the code

that will use this class. We've also used the addContent method here; with this,

we can add further content to the page (e.g. HTML that we've formatted ourselves,

outside the object). Finally, we have the get method, which is the only method

that returns a value. Once we've finished building the page, we'll use this to create

the HTML.

All these methods access the $page member variable, and this is no coincidence.

The ability to tie PHP code (the methods) to the data (the variables) that it works

on is the most fundamental feature of object oriented programming.

Here's the class in action:

File: 3.php (excerpt)

// Instantiate the Page class

$webPage = new Page();

// Add the header to the page

$webPage->addHeader('A Page Built with an Object');

[5] http://java.sun.com/