This document provides an overview of PHP classes and object-oriented programming. It defines what a class is conceptually and how to define a class in PHP, including defining attributes and methods. It explains how to instantiate class objects and use their methods. The document also covers class inheritance, constructors, and the differences between PHP4 and PHP5 object models.

1. PHP Classes
and
Object Orientation

2. Revision HIstory
#
Version
Date
Rationale for
change
1
1.0
26-Feb-2008
Initial Version
2
Change Description

3. Revision HIstory
Document Name
Training Material
Document Code
QMS-TEM-OT 08
Version
1.0
Date
26-Feb-2008
Created By
Ms. Padmavathy
Reviewed BY
SPG
Approved By
Mr. Vijay

4. Agenda
•
•
•
•
•
•
•
Introduction
Function
Class Definition
Class Usage
Constructor
Inheritance
PHP4 vs PHP5

5. Reminder… a function
• Reusable piece of code.
• Has its own ‘local scope’.
function my_func($arg1,$arg2) {
<< function statements >>
}

6. Conceptually, what does a
function represent?
…give the function something (arguments), it does
something with them, and then returns a result…
Action or
Method

7. What is a class?
Conceptually, a class represents an
object, with associated methods
and variables

8. Class Definition
<?php
class dog {
public $name;
public function bark() {
echo ‘Woof!’;
}
}
?>
An example class
definition for a dog.
The dog object has a
single attribute, the
name, and can
perform the action of
barking.

9. Class Definition
<?php
Define the name of the class.
class dog { class dog {
public $name;
public function bark() {
echo ‘Woof!’;
}
}
?>

10. Class Definition
<?php
class dog { public $name;
public $name;
public function bark() {
echo ‘Woof!’; Define an object attribute
(variable), the dog’s name.
}
}
?>

11. Class Definition
<?php
Define an object
action (function), the
class dog {
dog’s bark.
public $name;
public function bark() {
echo ‘Woof!’;
}
public function bark() {
echo ‘Woof!’;
}
}
?>

12. Class Defintion
Similar to defining a function..
The definition does not do anything by
itself. It is a blueprint, or description, of an
object. To do something, you need to use
the class…

13. Class Usage
<?php
require(‘dog.class.php’);
$puppy = new dog();
$puppy->name = ‘Rover’;
echo “{$puppy->name} says ”;
$puppy->bark();
?>

14. Class Usage
<?php require(‘dog.class.php’);
require(‘dog.class.php’);
$puppy = new dog();
$puppy->name = ‘Rover’;
Include the class definition
echo “{$puppy->name} says ”;
$puppy->bark();
?>

15. Class Usage
<?php
require(‘dog.class.php’);
$puppy = new dog();
$puppy = new dog();
$puppy->name = ‘Rover’;
echo “{$puppy->name} Create a new”; of the
says instance
class.
$puppy->bark();
?>

16. Class Usage
<?php
require(‘dog.class.php’);
$puppy = new dog();
$puppy->name = ‘Rover’;
$puppy->name = ‘Rover’;
echo “{$puppy->name} says ”;
Set the name variable of this
$puppy->bark();
instance to ‘Rover’.
?>

17. Class Usage
<?php
require(‘dog.class.php’); Use the name variable
of this instance in an
echo statement..
$puppy = new dog();
$puppy->name = ‘Rover’;
echo “{$puppy->name} says ”;
echo “{$puppy->name} says ”;
$puppy->bark();
?>

18. Class Usage
<?php
require(‘dog.class.php’);
Use the dog object
$puppy = new dog();
bark method.
$puppy->name = ‘Rover’;
echo “{$puppy->name} says ”;
$puppy->bark();
$puppy->bark();
?>

19. One dollar and one only…
$puppy->name = ‘Rover’;
The most common mistake is to use more
than one dollar sign when accessing
variables. The following means something
entirely different..
$puppy->$name = ‘Rover’;

20. Using attributes within the
class..
• If you need to use the class variables
within any class actions, use the special
variable $this in the definition:
class dog {
public $name;
public function bark() {
echo $this->name.‘ says Woof!’;
}
}

21. Constructor methods
• A constructor method is a function that is
automatically executed when the class is
first instantiated.
• Create a constructor by including a
function within the class definition with the
__construct name.
• Remember.. if the constructor requires
arguments, they must be passed when it
is instantiated!

22. Constructor Example
<?php
class dog {
public $name;
public function __construct($nametext) {
$this->name = $nametext;
}
public function bark() {
echo ‘Woof!’;
}
}
?>

23. Constructor Example
<?php
…
$puppy = new dog(‘Rover’);
…
?>
Constructor arguments are passed during the
instantiation of the object.

24. Class Scope
• Like functions, each instantiated object
has its own local scope.
e.g. if 2 different dog objects are
instantiated, $puppy1 and $puppy2, the
two dog names $puppy1->name and
$puppy2->name are entirely
independent..

25. Inheritance
• The real power of using classes is the
property of inheritance – creating a
hierarchy of interlinked classes.
dog
parent
children
poodle
alsatian

26. Inheritance
• The child classes ‘inherit’ all the methods
and variables of the parent class, and can
add extra ones of their own.
e.g. the child classes poodle inherits the
variable ‘name’ and method ‘bark’ from the
dog class, and can add extra ones…

27. Inheritance example
The American Kennel Club (AKC) recognizes three sizes of poodle - Standard,
Miniature, and Toy…
class poodle extends dog {
public $type;
public function set_type($height) {
if ($height<10) {
$this->type = ‘Toy’;
} elseif ($height>15) {
$this->type = ‘Standard’;
} else {
$this->type = ‘Miniature’;
}
}
}

28. Inheritance example
The American Kennel Club (AKC) recognizes three sizes of poodle - Standard,
Miniature, and Toy…
class poodle extends dog { class poodle extends dog {
public $type;
public function set_type($height) {
if ($height<10) {
Note the use of the extends keyword to
$this->type = ‘Toy’;
indicate that the poodle class is a child o
the dog class…
} elseif ($height>15) {
$this->type = ‘Standard’;
} else {
$this->type = ‘Miniature’;
}
}
}

29. Inheritance example
…
$puppy = new poodle(‘Oscar’);
$puppy->set_type(12); // 12 inches high!
echo “Poodle is called {$puppy->name}, ”;
echo “of type {$puppy->type}, saying “;
echo $puppy->bark();
…

30. …a poodle will always ‘Yip!’
• It is possible to over-ride a parent method with a new
method if it is given the same name in the child class..
class poodle extends dog {
…
public function bark() {
echo ‘Yip!’;
}
…
}

31. Child Constructors?
• If the child class possesses a constructor
function, it is executed and any parent
constructor is ignored.
• If the child class does not have a constructor,
the parent’s constructor is executed.
• If the child and parent does not have a
constructor, the grandparent constructor is
attempted…
• … etc.

32. Deleting objects
• So far our objects have not been
destroyed till the end of our scripts..
• Like variables, it is possible to explicitly
destroy an object using the unset()
function.

33. There is a lot more…
• We have really only touched the edge of
object orientated programming…
• But I don’t want to confuse you too much!

34. PHP4 vs. PHP5
• OOP purists will tell you that the object
support in PHP4 is sketchy. They are
right, in that a lot of features are missing.
• PHP5 OOP system has had a big
redesign and is much better.
…but it is worth it to produce OOP
code in either PHP4 or PHP5…