Approaches to Web Development for Bioinformatics

Medical Computing > Web Development for Bioinformatics > Web Development > PHP > OOP in PHP 4

Object Oriented Programming in PHP 4

Object oriented programming first appeared in PHP 4. The implementation was fairly minimal until PHP 5. Therefore, I will split the discussion on object oriented programming into two sections: one on PHP 4 and the other on PHP 5.

Object types (classes) can be defined with the class keyword:

PHP

<?php

/*
* An object encapsulating gene information
*/
class Gene_Info {

var $id; // The NCBI identifier field
var $symbol; // The gene symbol
var $name; // The name of the gene

function Gene_Info($myid, $mysymbol, $myname) {

$this->id = $myid;
$this->symbol = $mysymbol;
$this->name = $myname;

}

function get_id() {

return $this->id;

}

function get_symbol() {

return $this->symbol;

}

function get_name() {

return $this->name;

}

}

header('Content-Type: text/plain;charset=utf-8');

// Create a few Gene_Info objects and put them in an array
$hd = new Gene_Info(3064, "HD", "huntingtin (Huntington disease)");
$sry = new Gene_Info(6736, "SRY", "sex determining region Y");
$geneList = array($hd, $sry);

// Iterate over the Gene_Info objects and print them out
$count = count($geneList);
for ($i = 0; $i <$count; $i++) {

echo $geneList[$i]->get_id() . "\t" . $geneList[$i]->get_symbol() . "\t" .

$geneList[$i]->get_name() . "\n";

}

This example demonstrates a very language features. The name of the class or object type, Gene_Info, follows the class keyword. Inheritance can be used with the extends keyword but I will not demonstrate that. The Gene_Info class declares three member variables id, symbol, and name. The constructor is a method (function) with the same name as the class. It is invoked when a new object instance is created with the new keyword. Code within the class definition can use the $this psuedo variable to access member variables (not the absence of the $ for member variables). The program output is

Pogram output

3064 HD huntingtin (Huntington disease)
6736 SRY sex determining region Y

Objects can be serialized with the predefined function serialize(). This is useful for storing them in a user session. They can be unserialized with the predefined unserialize() function.

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