Demystifying Object-Oriented Programming - Midwest PHP

DEMYSTIFYING OBJECT-ORIENTED
PROGRAMMING
MAKING SENSE OF ALL THE MUMBO JUMBO
HTTPS://GITHUB.COM/SKETCHINGS/OOP-BASICS

TERMINOLOGY
THE SINGLE MOST IMPORTANT PART

TERMS
• Class (properties, methods)
• Object
• Instance
• Abstraction
• Encapsulation

TERMS CONTINUED
• Polymorphism
• Inheritance
• Interface
• Abstract Class
• Traits
• Namespaces

CLASS
• A template/blueprint that facilitates creation of objects.
A set of program statements to do a certain task. Usually
represents a noun, such as a person, place or thing.
• Includes properties and methods — which are class
functions

OBJECT
• Instance of a class.
• In the real world object is a material thing that
can be seen and touched.
• In OOP, object is a self-contained entity that
consists of both data and procedures.

INSTANCE
• Single occurrence/copy of an object
• There might be one or several objects, but an
instance is a speciﬁc copy, to which you can have
a reference

class User { //class 
private $name; //property 
public getName() { //method 
echo $this->name; 
} 
}
$user1 = new User(); //ﬁrst instance of object
$user2 = new User(); //second instance of object

ABSTRACTION
• “An abstraction denotes the essential characteristics
of an object that distinguish it from all other kinds of
object and thus provide crisply deﬁned conceptual
boundaries, relative to the perspective of the
viewer.” 
— G. Booch
• This is the class architecture itself.
• Use something without knowing exactly how it works

ENCAPSULATION
• Scope. Controls who can access what. Restricting
access to some of the object’s components (properties
and methods), preventing unauthorized access.
• Public - everyone
• Protected - inherited classes
• Private - class itself, not children

class User { 
protected $name; 
protected $title; 
public function getFormattedSalutation() { 
return $this->getSalutation(); 
} 
protected function getSalutation() { 
return $this->title . " " . $this->name; 
} 
public function getName() { 
return $this->name; 
} 
public function setName($name) { 
$this->name = $name; 
} 
public function getTitle() { 
return $this->title; 
} 
public function setTitle($title) { 
$this->title = $title; 
} 
}

CREATING / USING THE OBJECT INSTANCE
$user = new User(); 
$user->setName("Jane Smith"); 
$user->setTitle("Ms"); 
echo $user->getFormattedSalutation();
When the script is run, it will return:
Ms Jane Smith

CONSTRUCTOR METHOD & MAGIC METHODS
class User { 
protected $name; 
protected $title; 
 
public function __construct($name, $title) { 
$this->name = $name; 
$this->title = $title; 
} 
 
public function __toString() { 
return $this->getFormattedSalutation(); 
} 
... 
}
For more see http://php.net/manual/en/language.oop5.magic.php

CREATING / USING THE OBJECT INSTANCE
$user = new User("Jane Smith","Ms"); 
echo $user;
When the script is run, it will return the same result as before:
Ms Jane Smith

POLYMORPHISM
DRY and Sharing Code

INHERITANCE: PASSES KNOWLEDGE DOWN
• Subclass, parent and a child relationship, allows for
reusability, extensibility.
• Additional code to an existing class without modifying it.
Uses keyword “extends”
• NUTSHELL: create a new class based on an existing class
with more data, create new objects based on this class

CREATING AND USING A CHILD CLASS
class Developer extends User { 
public $skills = array(); 
public function getSalutation() { 
return $this->title . " " . $this->name. ", Developer"; 
} 
public function getSkillsString() { 
echo implode(", ",$this->skills); 
} 
}
$developer = new Developer("Jane Smith", "Ms"); 
echo $developer; 
echo "<br />"; 
$developer->skills = array("JavasScript", "HTML", "CSS"); 
$developer->skills[] = "PHP"; 
$developer->getSkillsString();

WHEN RUN, THE SCRIPT RETURNS:
Ms Jane Smith, Developer
JavasScript, HTML, CSS, PHP

INTERFACE
• Interface, speciﬁes which methods a class must implement.
• All methods in interface must be public.
• Multiple interfaces can be implemented by using comma
separation
• Interface may contain a CONSTANT, but may not be
overridden by implementing class

interface UserInterface {
public function getFormattedSalutation();
public function getName();
public function setName($name);
public function getTitle();
public function setTitle($title);
}
class User implements UserInterface { … }

ABSTRACT CLASS
An abstract class is a mix between an interface and a class. It can deﬁne
functionality as well as interface.
Classes extending an abstract class must implement all of the abstract
methods deﬁned in the abstract class.

abstract class User { //class
public $name; //property
public getName() { //method
echo $this->name;
}
abstract public function setName($name);
}
class Developer extends User { … }

COMPOSITION
Horizontal Code Reuse

TRAITS
• Multiple traits can be implemented

CREATING TRAITS
trait Toolkit { 
public $tools = array(); 
public function setTools($task) { 
switch { 
case “eat": 
$this->tools[] = ("Spoon", "Fork", "Knife"); 
exit; 
... 
} 
} 
public function showTools() { 
echo implode(", ",$this->skills); 
} 
}

USING TRAITS
class Developer extends User { 
use Toolkit; 
 
... 
}
$developer = new Developer("Jane Smith", "Ms"); 
echo $developer; 
echo "<br />"; 
$developer->setTools("Eat"); 
echo $developer->showTools();

WHEN RUN, THE SCRIPT RETURNS:
Ms Jane Smith
Spoon, Fork, Knife

NAMESPACES
Prevent Code Collision

NAMESPACES
• Help create a new layer of code encapsulation
• Keep properties from colliding between areas of your code
• Only classes, interfaces, functions and constants are
affected
• Anything that does not have a namespace is considered in
the Global namespace (namespace = "")

NAMESPACES
• Must be declared first (except 'declare)
• Can define multiple in the same file
• You can define that something be used in the "Global" namespace by
enclosing a non-labeled namespace in {} brackets.
• Use namespaces from within other namespaces, along with aliasing

• namespace myUser;
• class User { //class
• public $name; //property
• public getName() { //method
• echo $this->name;
• }
• public function setName($name);
• }
• class Developer extends myUserUser { … }

EXPLANATION COMPLETE
QUESTION AND ANSWER TIME

ALENA HOLLIGAN
@sketchings 
sketchings.com
Wife and Mother of 3 young children  
PHP Teacher at Treehouse 
PHP Users Group Leader 
Women Who Code Leader
https://joind.in/talk/6b753

CHALLENGES
1. Change to User class to an abstract class.
2. Throw an error because your access is too restricted.
3. Extend the User class for another type of user, such as our
Developer example
4. Deﬁne 2 “User” classes in one ﬁle using namespacing
https://github.com/sketchings/oop-basics

RESOURCES
• LeanPub: The Essentials of Object Oriented PHP
• Head First Object-Oriented Analysis and Design

Demystifying Object-Oriented Programming - Midwest PHP

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