This document provides an overview of object-oriented programming concepts in PHP, including classes, instances, properties, methods, constructors, and special methods. A class defines the blueprint for an object, while an instance refers to an actual object in memory. Classes contain properties to store data and methods to implement behaviors. Constructors are special methods that run when a new object is created.

1. Beginning PHP
Session #6
January 5, 2011
Josh Butts

2. Agenda
• Freebies from Zend
• OOP

3. What are Objects
• Programming constructs
• Represent a real-life entity
• Store data (state)
• Implement behaviors

4. Object Oriented
Programming
• ...programming with objects
• Use objects to model real world concepts
in your code
• Objects encapsulate pieces of logic or data
• Objects are easy to re-use

5. Terms
• Class - the definition of an object; what
does it represent, what can it do
• Instance - an actual object variable in
memory

6. Classes & Instances
• A class is defined in code as you write your
program
• An instance happens when you program
actually runs

7. Example
User Class
Instance of User
$username
$password
jimbojsb
$email
password
$firstname
josh@joshbutts.com
$lastname
Josh
Butts
authenticate()
createPassword()
getPosts()

8. Classes & Instances
• A class is defined in code as you write your
program
• An instance happens when you program
actually runs

9. “Static”
• Static describes a class or part of a class
that can be used without actually creating
an instance and filling it with data
• Pieces of data that are the same for every
instance of a class
• Logic that operates on generic data rather
than modifying a specific instance’s state

10. Building Objects
• Properties (variables)
• Methods (functions)
• Methods & Properties can both be static or
not

11. Constructors
• A special method (1 per object) that gets
called when you get a new instance
• Does any utility or setup work needed
before the instance is ready to be used
• Optional
• Usually take one or more parameters

12. PHP Objects
• Preferably you define one class per file
• Objects are always passed by reference
instead of by value
• :: operator is used for static properties and
methods
• -> operator is used for instance properties
and methods

13. PHP Objects
• self - refers to the current object in a static
manner
• $this - refers to the current instance

14. Special Methods
• __construct()
• __destruct()
• __toString()
• many others, for a later discussion