Web Programming Step by Step

Lecture 12
Object-Oriented PHP

References: PHP.net, Developer.com, KillerPHP, DevX

Except where otherwise noted, the contents of this presentation are Copyright 2009 Marty Stepp and Jessica Miller.

Valid XHTML 1.1 Valid CSS!

Why use classes and objects?

Constructing and using objects

# construct an object
$name = new ClassName(parameters);

# access an object's field (if the field is public)
$name->fieldName

# call an object's method
$name->methodName(parameters);
$zip = new ZipArchive();
$zip->open("moviefiles.zip");
$zip->extractTo("images/");
$zip->close();

Object example: Fetch file from web

# create an HTTP request to fetch student.php
$req = new HttpRequest("student.php", HttpRequest::METH_GET);
$params = array("first_name" => $fname, "last_name" => $lname);
$req->addPostFields($params);

# send request and examine result
$req->send();
$http_result_code = $req->getResponseCode();   # 200 means OK
print "$http_result_code\n";
print $req->getResponseBody();

Class declaration syntax

class ClassName {
	# fields - data inside each object
	public $name;    # public field
	private $name;   # private field
	
	# constructor - initializes each object's state
	public function __construct(parameters) {
		statement(s);
	}
	
	# method - behavior of each object
	public function name(parameters) {
		statements;
	}
}

Class example

<?php
class Point {
	public $x;
	public $y;
	
	# equivalent of a Java constructor
	public function __construct($x, $y) {
		$this->x = $x;
		$this->y = $y;
	}
	
	public function distance($p) {
		$dx = $this->x - $p->x;
		$dy = $this->y - $p->y;
		return sqrt($dx * $dx + $dy * $dy);
	}
	
	# equivalent of Java's toString method
	public function __toString() {
		return "(" . $this->x . ", " . $this->y . ")";
	}
}
?>

Class usage example

<?php
# this code could go into a file named use_point.php
include("Point.php");

$p1 = new Point(0, 0);
$p2 = new Point(4, 3);
print "Distance between $p1 and $p2 is " . $p1->distance($p2) . "\n\n";

var_dump($p2);   # var_dump prints detailed state of an object
?>
Distance between (0, 0) and (4, 3) is 5

object(Point)[2]
  public 'x' => int 4
  public 'y' => int 3

Basic inheritance

class ClassName extends ClassName {
	...
}
class Point3D extends Point {
	public $z;
	
	public function __construct($x, $y, $z) {
		parent::__construct($x, $y);
		$this->z = $z;
	}
	
	...
}

Static methods, fields, and constants

static $name = value;    # declaring a static field
const $name = value;     # declaring a static constant
# declaring a static method
public static function name(parameters) {
	statements;
}
ClassName::methodName(parameters);  # calling a static method (outside class)
self::methodName(parameters);       # calling a static method (within class)

Abstract classes and interfaces

interface InterfaceName {
	public function name(parameters);
	public function name(parameters);
	...
}

class ClassName implements InterfaceName { ...
abstract class ClassName {
	abstract public function name(parameters);
	...
}