PHP Classes and Object Orientation

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

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) {

• >

• }

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 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 class dog { Define the name of the class.

Class Definition public $name; Define an object attribute (variable), the dogs name.

Class Definition public function bark() { echo Woof! ; } Define an object action (function), the dogs 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

Class Usage require ( dog.class.php ); Include the class definition

Class Usage $puppy = new dog(); Create a new instance of the class.

Class Usage $puppy->name = Rover ; Set the name variable of this instance to Rover.

Class Usage echo {$puppy->name} says ; Use the name variable of this instance in an echo statement..

Class Usage $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

Constructor Example 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 ($heighttype = Toy ; } elseif ($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 ($heighttype = Toy ; } elseif ($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 parents 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 dont 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

Thank you