(An Extended) Beginners Guide to Object Orientation In PHP

byRick Ogden

http://www.rickogden.com/

Drinking Game

Take a drink when:I mention class, object, method, property

Every time a piece of example code is displayed

Finish your drink when:I accidentally say function instead of method

What is Object Orientation?

Object-Oriented Programming is a programming methodology that consists of multiple interacting objects, each completely self-sufficient.

This allows for flexible, expandable programming

Encapsulated code

Protection of data

Many more things beyond the scope of this tutorial

Mindset

With OO you need quite a different mindset to programming using procedural methodology.

You need to think about things as entities:What each entity is

What each entity does

What each entity needs

From there you can go on to realise your ideas in Classes, which will in turn be instantiated into Objects

Examples of Objects

Examples of Objects

Examples of Objects

Class

A class is a blueprint of an object, and is the basis of what the object will consist of.

It contains two major entities:Properties

Methods

A class is self sufficient by nature, and therefore can be implemented into multiple applications without modification.

Example of a Class

Here we're going to create a new class for containing someone's profile information on a social networking website.

Object

An object is created by creating a new instance of a class.

Objects of the same class have exactly the same functionality, but the properties within the object are what makes them different.

Eg.A news article on a website may be an object from a NewsArticle class, but the contents of the article will differ from another news article

Referencing

In order for an object to be useful, you need to be able to call its contents. For this, PHP uses the arrow operator ( -> ).

$object->property;

$object->method();

Self Referencing

Throughout the instance of an object, chances are it will need to reference itself (to get its properties, or call its own methods). In order for an object to reference itself, the variable $this is used in the class.

$this->property;

$this->method();

Properties

Properties are class-wide variables.

They are often initialised when an object of the class is created (although they do not have to be)

They are defined at the top of the class

Methods can alter and interact with these properties throughout the existence of the object

Adding Properties

We will add some properties to our Profile class. Of course the properties are not limited to the ones here:

Methods

A method is a piece of code within a class which performs a task or calculation. These are similar to functions.It can:Interact and modify properties of the object (set)

Take arguments on execution

Return a value after execution (get)None of these are compulsory (although if it doesn't do any of these, it's a bit useless!)

Method Uses

Methods are used for a number of different things. These include:Retrieve data from a property in a read only fashion

Format data

Alter properties in a controlled way

Method: Parameters

A method can include parameters (exactly like functions)

Parameters can either be required, or have a default value

Constructor

The constructor is called when the object is initialised.A constructor often takes parameters to initialise some (if not all) of the properties of that object

It is identified in a class as it has the method name __construct (for backwards-compatibility, a method with the same name as the class also works)

Our class so far

I've added a constructor to initialise the properties

Added a method to return the full name of the person whose profile it is.

Profile.php

Instantiate an Object

To create an object from a class you use the new keyword.$object = new MyClass();

This creates a new object and calls the constructor

Any arguments that need to be given to the constructor are given on creation.

We will store our class in Profile.php

controller.php

Execute Program

Execute Program

Encapsulation

Why Use Encapsulation

Encapsulation gives the ability to hide data from outside of the object.Gives the programmer control over what is inputted into properties (validation etc..)

What form data is when it is returned from the class

Ability to alter code within the class, without having to worry about needing to change code in other parts of the application

Public/Private/Protected

Properties and methods can take one of 3 forms to encapsulatePublic: Property/method can be accessed from anywhere, inside or outside the object

Protected: Can only be accessed from within the class, or inherited class

Private: Can only be accessed from directly within the class (and not subclasses)

controller

Execute the Controller

Execute the Controller

Attempt to access Private Property

Attempt to access Private Property

Inheritance

Inheritance

Inheritance allows a programmer to reuse a class and expand it for a different purpose.Reasons:Add code to a class to make it more specialised

Override existing code

Why reinvent the wheel?

Execute

Execute

Fluent Interfaces

An accessor method by its nature must return a value a mutator method does not.

Fluent Interfaces are a convenience for programmers (who are inherently lazy) to perform multiple mutations in one statement.

$myObject->changeSurname('Ogden')->changeForename('Rick');

Fluent Interfaces

This is achieved by having methods return this

Any method that returns this can have a method call appended to it.

return $this;

Instance Control

What happens if you want to make sure if you only want one instance of a Class?

Eg Database connection

Use a Singleton!

This is achieved using a static method.

Static Method

Static methods (unlike standard methods) can be called at the Class level. This means it does not require an object to be created for it to be called.

This can be used to control the creation and use of an object.

Static Referencing

As static methods are not part of objects, you do not use an arrow. You use a double colon:

$object->method();

Class::method();

Also, for self referencing within the class, the keyword self is used (sort of like $this).

Singleton Example

Get/Create Singleton

As there can only ever be one instance of a singleton, creation of instance and retrieval of instance is done by the same (static) method.

From there on, the object can be interacted with as normal

Cons of Object Orientation

Object Orientation does not come without its drawbacks

Main reason is it is less efficient than procedural code

For smaller projects, often means writing more code

Thank You

Any (other) questions?

For these slides, example code and other things please visit my website:
http://www.rickogden.com/

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