PHP Classes and Object Orientation
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PHP Classes and
Object Orientation
# Version DateRationale for change
Change Description
1 1.0 26-Feb-2008 Initial Version
2
Revision HIstory
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
Agenda
• Introduction• Function• Class Definition• Class Usage• Constructor • Inheritance• PHP4 vs PHP5
Reminder… a function
• Reusable piece of code.
• Has its own ‘local scope’.
function my_func($arg1,$arg2) {
<< function statements >>
}
Conceptually, what does a function represent?
…give the function something (arguments), it does something with them, and then returns a result…
Action or Method
What is a class?
Conceptually, a class represents an object, with associated methods
and variables
Class Definition
<?phpclass 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.
Class Definition
<?phpclass dog {public $name;public function bark() {echo ‘Woof!’;
}} ?>
class dog {
Define the name of the class.
Class Definition
<?phpclass dog {public $name;public function bark() {echo ‘Woof!’;
}} ?>
public $name;
Define an object attribute (variable), the dog’s name.
Class Definition
<?phpclass dog {public $name;public function bark() {echo ‘Woof!’;
}} ?>
public function bark() {echo ‘Woof!’;
}
Define an object action (function), the dog’s bark.
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…
Class Usage
<?php
require(‘dog.class.php’);
$puppy = new dog();
$puppy->name = ‘Rover’;
echo “{$puppy->name} says ”;
$puppy->bark();
?>
Class Usage
<?php
require(‘dog.class.php’);
$puppy = new dog();
$puppy->name = ‘Rover’;
echo “{$puppy->name} says ”;
$puppy->bark();
?>
require(‘dog.class.php’);
Include the class definition
Class Usage
<?php
require(‘dog.class.php’);
$puppy = new dog();
$puppy->name = ‘Rover’;
echo “{$puppy->name} says ”;
$puppy->bark();
?>
$puppy = new dog();
Create a new instance of the class.
Class Usage
<?php
require(‘dog.class.php’);
$puppy = new dog();
$puppy->name = ‘Rover’;
echo “{$puppy->name} says ”;
$puppy->bark();
?>
$puppy->name = ‘Rover’;
Set the name variable of this instance to ‘Rover’.
Class Usage
<?php
require(‘dog.class.php’);
$puppy = new dog();
$puppy->name = ‘Rover’;
echo “{$puppy->name} says ”;
$puppy->bark();
?>
echo “{$puppy->name} says ”;
Use the name variable of this instance in an echo statement..
Class Usage
<?php
require(‘dog.class.php’);
$puppy = new dog();
$puppy->name = ‘Rover’;
echo “{$puppy->name} says ”;
$puppy->bark();
?>
$puppy->bark();
Use the dog object bark method.
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’;
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!’; }}
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!
Constructor Example
<?phpclass dog {
public $name;public function __construct($nametext) {
$this->name = $nametext;} public function bark() {
echo ‘Woof!’;}} ?>
Constructor Example
<?php
…
$puppy = new dog(‘Rover’);
…
?> Constructor arguments are passed during the instantiation of the object.
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..
Inheritance
• The real power of using classes is the property of inheritance – creating a hierarchy of interlinked classes.
dog
poodle alsatian
parent
children
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…
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’;}
}}
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’;
} }}
class poodle extends dog {
Note the use of the extends keyword to indicate that the poodle class is a child of the dog class…
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();
…
…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!’;}…
}
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.
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.
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!
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…
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