Month: November 2011

Final and auto load a class

To include a class within many languages you have to define it at the top and then off you go with programming with using that class. Well within PHP you can use the __autoload function that is called when you try to create a new instance of a class.

function __autoload($class_name) 
{
	include "classes/".$class_name.".php";
}

this __autoload function above takes a parameter as the class name to load and then within the code it will try and load that class with how ever you want to, in this case I have placed the classes within the directory called classes and under there classname.php filename.

So if you try to load the class

$newclass = new basic();

it will look within the classes directory for the file basic.php for the autoload function above, you can alter it to load from where ever and how ever you want to.

The next part of this post is about the keyword ‘final’, the final keyword means that it is final so if you try and extend that class and extend the function that has been declared as final this will cause php interpretor to fail due to syntax error with something similar to

Fatal error: Cannot override final method class_name::function_name()

For an example here is two classes one is called basic and the other is called extendbasic, where the basic class has the final function within it

class basic
{
	public function sayHello()
	{
		echo "<br/>".get_class($this) . " : Hello";
	}
 
	final public function sayGoodbye()
	{
		echo "<br/>".get_class($this) . " : Goodbye";
	}
}

and here is the extendclass

class extendbasic extends basic
{
	public function sayHello()
	{
		echo "<br/>".get_class($this). " : the newer hello!!";	
		parent::sayHello();
	}
        // this will cause the php engine to fail!!!!!. because it is trying to over load the function sayGoogbye which has been declared as final
/*	public function sayGoodbye()
	{
		echo "I should not get here!!";
	}*/
}

Here is some code to call them both which they have been placed within a directory called ‘classes’

function __autoload($class_name) 
{
	include "classes/".$class_name.".php";
}
 
$basicClass = new basic();
$basicClass->sayHello();
$basicClass->sayGoodbye();
$basicClass = new extendbasic();
$basicClass->sayHello();
$basicClass->sayGoodbye();

and the output would be

basic : Hello
basic : Goodbye
extendbasic : the newer hello!!
extendbasic : Hello
extendbasic : Goodbye

I am calling the parent function from within the extendbasic class sayHello function.

Node – install and test

One of my friends asked me what is Node and also how do you install and test to make sure it is working.

Well, Node is in essence a javascript server side environment that allows you to write code that will allow the event model to handle requests very quickly since it does not handle the I/O (well almost of all of the functions within node do not!) so there is no-blocking of code.

Node has a very quick and capable http class that allows for the user to create a server that is capable of doing some very quick responses to multiple connections.

To install Node you just need to do this in ubuntu

sudo -s
apt-get install python-software-properties
add-apt-repository ppa:chris-lea/node.js
apt-get update
apt-get install nodejs
exit

the first line allows you to be the root and thus the next commands are as the user root.

Or if you are using windows just download the executable from here

To test the node to make sure it is working with a basic “Hello world!” example if you save this below as helloworld.js.

var http = require("http");
// create the http server function req'uest, res'ult
http.createServer(function (req, res) 
{
    // 200 = means http response code of found page, then a array of the content type
    res.writeHead(200, {'Content-Type' : 'text/plain'});
    res.end('Hello world!');  // write out the text
}).listen(8080,'127.0.0.1');
// listen on port 8080 on the ip address 127.0.0.1
console.log('We have started, check your browser on http://127.0.0.1:8080/');

I am using a higher number than 1024 for the port because below that you need to be a root user or administrator on windows to allow anything to connect to those port numbers.

So if you now run the program with the javascript file above as the second parameter

node helloworld.js

and then if you open your browser at 127.0.0.1:8080 then you will see

Hello world!