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Why objects?

PHP scripts become more and more complex, the difficulty of maintaining them increases dramatically especially if you are programming in a procedural style which is < php4.
php4 and php5 have been completely redesigned to meet OOP evolution.

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Creating basic classes

A class can be thought of as a blueprint of an object and defines all the actions that object is capable of.
Class definitions thus contain variables, functions (called methods), and even constants that are specific to that class or its instances only

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Implementation of OOP

Create a class

Create an instance of class

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Implementation of OOP

Accessing the instance object

calls the my_method() method of the class, the following output will be generated as:

Hello, you called my_method(MyParam)!

The value of my variable is 10

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Private and Public

Public : Class members can be accessed from anywhere within a script.

can be called or modified internally by the object or from outside the object.

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Private and Public

Private: access to the class member only from within an instance of that class through the $this variable

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Constructors and Destructors

Functions that are called when a new instance of an object is created (constructors) and/or destroyed (destructors).
Purpose is to allow for a means to initialize and clean up after an object during its use.

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Class Constants

A facility to define constant values within a class definition

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Static Methods

Methods that are part of a class, but that are designed to be called from outside the context of the instance of an object.
Cannot use the $this variable to reference the current instance of the object
To create a static method, add the static keyword in front of any class method declaration:

static function myMethod() {

... }

To call a static method, the syntax is as follows:

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Class Inheritance

Capability for one class definition to extend another class definition's functionality.
When one class inherits from another, all of the parent's methods, properties, and constants are available from the child class as well.
Child classes can also reimplement some or all of the methods, properties, and constants of a parent class to provide additional or different functionality.
Classes are inherited from one another using the extends keyword in the class definition.

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Example inheritance

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Class member overloading

When the preceding script is executed, what will happen?

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Class Member Binding

When the callMe() method is called, what will happen?

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Advanced classes

Abstract Classes and Methods

To provide a superclass that defines the abstract characteristics of classes that inherit from it.
May or may not actually contain any code within them, and they can never be instantiated directly.

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Example Abstract Classes

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Interfaces

Designed to assure functionality within a class.
To define a set of methods a class claiming to implement that interface must have.
Example

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Implementing Interfaces

A class that implements an interface

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Final Classes and Methods

Used to provide control over inheritance.
Classes or methods declared as final cannot be extended and/or overloaded by child classes.
To ensure that a particular class or method is never overloaded, �simply add the �final keyword to �the method or �class definition

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Special methods

Getters and Setters

to provide a catch-all interface when accessing properties in objects.

The __call() Method

used to provide a catch-all for method calls within an object.

The __toString() Method

to provide an easy way to access the string representation of a complex object.

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Getters and Setters

These methods, named __get() and __set() respectively, will be called when a particular property was not defined.
The prototype for these special methods are as follows:

Getter and setter methods are useful when dealing with Web services or container objects where the properties available within an instance of a class may not be completely known until the execution of the script.

function __get($name);

function __set($name, $value);

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The __call() Method

When an attempt to call a method not previously defined within the class is received, if possible the __call method will be called.
The prototype of this method is as follows:

useful when a complete function list is not available until the execution of the script.
another application of the __call() method is to provide a catch-all method to handle attempts to call invalid methods

function __call($method, $arguments);

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Using the __call() Method

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The __toString() Method

When defined, PHP will call this method under certain circumstances when the object would be better treated as a string
The value of the string returned by the __toString() method can be anything

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Using the __toString() Method

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Class autoloading

To specify a function to load classes as they are needed, if desired.
This function is called the __autoload() function and has a prototype as follows:

function __autoload($classname);

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Using the __autoload() Function

This example used to load classes by looking up their location in a predefined associative array. Because neither MyClass nor anotherClass has been defined yet in this script, the __autoload() function will be called in both instances to give the script an opportunity to find the class itself