Object Oriented PHP5

OBJECT-ORIENTED PRINCIPLES
WITH PHP5

Jason Austin - @jason_austin

TriPUG Meetup - Jan 18, 2011

Goals

Explain object-oriented concepts

Introduce PHP5’s object oriented interface

Illustrate how object-oriented programming can help you

Help you write better code

What makes good software?

"The function of good software is to make the complex
appear to be simple." - Grady Booch

"Always code as if the guy who ends up maintaining your
code will be a violent psychopath who knows where you
live." - Martin Golding

Good software needs good software engineering

Software engineering != programming

“Programming is just typing” - Everette Allen

What is software engineering then?

Software engineering is the application of a systematic,
quantiﬁable, disciplined approach to development.

Programming is simply one phase of development

PHP & Software Engineering

PHP is quick to learn, almost to a fault

Easy to write bad code

However, PHP provides tools to facilitate the creation of
solid and organized software

PHP started as a procedural language, but has evolved!

Procedural Code

<?php
include “config.php”;
include “display.php”;
mysql_connect($host, $user, $pass);
echo “<html>”;
echo “ <head>”;
echo “ <title>Page</title>”;
echo “ </head>”;
echo “ <body>”;
printMenu();
$result = mysql_query(“Select * from news”);
printContent($result);
echo “</body></html>”;
?>

What’s Wrong With That!?

Nothing is really wrong with it. But...

It’s really hard to read and follow

As the code base grows, maintainability decreases

New additions often become hacks

Designers can’t easily design unless they know PHP

How else would I do it?!

Object Oriented Programming FTW!

What is OOP?

Programming paradigm using “objects” and their interactions

Not really popular until 1990’s

Basically the opposite of procedural programming

When would I use this OOP stuff?

When you...

ﬁnd yourself repeating code

want to group certain functions together

want to easily share some of your code

want to have an organized code base

think you may reuse some of your code later

Why OOP?

code resuse!!!

maintainability

code reuse!!!

readability

code reuse!!!

OOP Techniques

Before we get to the code, a little OOP primer

Encapsulation

Modularity

Inheritance

Polymorphism

Encapsulation (It’s like a Twinkie!)
Group together data and functionality (bananas and cream)

Hide implementation details (how they get the ﬁlling in there)

Provide an explicitly deﬁned
way to interact with the data
(they’re always the same shape)

Hides the creamy center!

Modularity (It’s like this sofa!)

A property of an application that measures the extent to
which the application has been composed of separate parts
(modules)

Easier to have a more
loosely-coupled application

No one part is programatically
bound to another

Inheritance (It’s like Joan & Melissa Rivers)

A hierarchical way to organize data and functionality

Children receive functionality and properties of their
ancestors

is-a and has-a relationships

Inherently (hah!) encourages
code reuse

Polymorphism (It’s like that guy)

Combines all the other techniques

Kind of complicated so we’ll get to
it later

Need to know terms

class - A collection of interrelated functions and variables
that manipulates a single idea or concept.

instantiate - To allocate memory for a class.

object - An instance of a class

method - A function within a class

class member - A method or variable within a class

What does a class look like?
<?php

// this is a class. $name and getHeight() are class members

class Person
{
public $name = “Bob McSmithyPants”; // this is a class variable

public function getHeight() // this is a class method
{}
}
?>

How to instantiate a class

<?php
$p = new Person(); // at this point $p is a new Person object
?>

Now anyone can use the Person object (call its methods,
change its variables, etc.)

Protecting Your Stuff

What if you want to keep methods and data from being changed?

Scoping

Foundation of OOP

Important for exposing functionality and data to users

Protect data and method integrity

Scopes

public

private

protected

Public
Anyone (the class itself or any instantiation of that class) can have access to the
method or property

If not speciﬁed, a method or property is declared public by default

Public Example
<?php

class Person
{
public function getName()
{
return “Bob McSmithyPants”;
}
}
?>

<?php

$p = new Person();
echo $p->getName();
?>

Private
Only the class itself has access to the method or property

Private Example
<?php

class Person
{
public function firstName()
{
return “Bob”;
}

private function lastName()
{
return “McSmithyPants”;
}
}
?>

<?php
$p = new Person();
echo $p->firstName(); // this will work
echo $p->lastName(); // this does not work
?>

Protected
Only the class itself or a class that extends this class can
have access to the method or property

Protected Example
<?php

class Person
{
protected function getName()
{
}
}

class Bob extends Person
{
public function whatIsMyName()
{
return $this->getName();
}
}
?>

<?php
$p = new Person();
echo $p->getName(); // this won’t work

$b = new Bob();
echo $b->whatIsMyName(); // this will work
?>

What was with that $this stuff?

You can access the protected data and methods with “object
accessors”

These allow you to keep the bad guys out, but still let the good
guys in.

Object Accessors

Ways to access the data and methods from within objects

$this

self

parent

$this
variable

refers to the current instantiation
<?php

class Person
{
public $name = ‘bob’;

{
return $this->name;
}
}

$p = new Person();
echo $p->getName();

// will print bob
?>

self
keyword that refers to the class itself regardless of
instantiation status

not a variable
<?php

class Person
{
public static $name = ‘bob’;

{
return self::$name;
}
}

$p = new Person();
echo $p->getName();

// will print bob
?>

parent
<?php

class Person keyword that refers to the parent class
{
public $name = ‘bob’;
most often used when overriding
{ methods
return $this->name;
}
} also not a variable!
{ What would happen if we used
{ $this->getName() instead of
}
return strtoupper(parent::getName()); parent::getName()?
}

$bob = new Bob();
echo $bob->getName();

// will print BOB
?>

Class constants

Deﬁned with the “const” keyword

Always static

Not declared or used with $

Must be a constant expression, not a variable, class member,
result of a mathematical expression or a function call

Must start with a letter

Constant Example

<?php

class DanielFaraday
{
const MY_CONSTANT = 'Desmond';

public static function getMyConstant()
{
return self::MY_CONSTANT;
}
}

echo DanielFaraday::MY_CONSTANT;

echo DanielFaraday::getMyConstant();

$crazyTimeTravelDude = new DanielFaraday();
echo $crazyTimeTravelDude->getMyConstant();

?>

Class and Method Properties

Final and Static

Classes and methods can be declared either ﬁnal, static, or
both!

Important Note!

Class member scopes (public, private, and protected) and
the class and method properties (ﬁnal and static) are not
mutually exclusive!

Final

Properties or methods declared ﬁnal cannot be overridden by a subclass

Final Example
<?php

class Person
{
public final function getName()
{
return “Steve Dave”;
}
}

{
{
}
}

// this will fail when trying to include Bob
?>

Static

A method declared as static can be accessed without
instantiating the class

You cannot use $this within static functions because $this
refers to the current instantiation

Accessed via the scope resolution operator ( :: )

i.e. – About::getVersion();

Static Example
<?php

class About
{
public static function getVersion()
{
return “Version 2.0”;
}
}
?>

<?php echo About::getVersion(); ?>

Types of Classes

Abstract Class

Interface

Abstract Classes

Never directly instantiated

Any subclass will have the properties and methods of the
abstract class

Useful for grouping generic functionality of subclassed
objects

At least one method must be declared as abstract

Abstract Example
<?php
<?php
abstract class Car
{ $honda = new Honda();
private $_color; $honda->setColor(“black”);
$honda->drive();
abstract public function drive();
?>
public function setColor($color)
{
$this->_color = $color;
}

public function getColor()
{
return $this->_color;
}
}

class Honda extends Car
{
public function drive()
{
$color = $this->getColor();
echo “I’m driving a $color car!”;
}
}
?>

Interfaces

Deﬁnes which methods are required for implementing an
object

Speciﬁes the abstract intention of a class without providing
any implementation

Like a blueprint or template

A class can simultaneously implement multiple interfaces

Interface Example
<?php
<?php
interface Car
{ $honda = new Honda();
public function start(); $honda->start();
public function drive(); $honda->drive();
public function stop(); $honda->stop();
} ?>

class Honda implements Car
{
public function start()
{
echo “Car is started!”;
}
public function drive()
{
echo “I’m driving!”;
}
public function stop()
{
echo “The car has stopped!”;
}
}
?>

instanceof

Operator to check if one class is an instance of another class
<?php
<?php
class Car
class Car
{}
{}
{}
{}
$car = new Car(); OR $car = new Honda();
$honda = new Honda();
if ($car instanceof Car) {
if ($car instanceof $honda) {
echo “true”;
echo “true”;
} else {
} else {
echo “false”;
echo “false”;
}
}
?>
?>

What will get printed?

Type Hinting

PHP is not strongly typed (i.e. - variables can be
pretty much anything anytime)

In PHP4 you have to do a lot of checking
to ﬁnd out if a parameter is the correct type

Type Hinting helps make this more efﬁcient

Type Hinting Example
<?php
// this can be made better with type hinting!
public function promoteToManager($bob)
{
if (!is_a($bob, “Person”)) {
throw new Exception(“$bob is not a Person!”);
}
// do stuff with $bob
}
?>

... becomes ...
<?php
// this is better!
public function promoteToManager(Person $bob)
{
// do stuff with $bob
}
?>

A Few More Terms

serialize - Converting an object to a binary form (i.e. -
writing an object to a ﬁle)

unserialize - The opposite of serialize. To convert the
stored binary representation of an object back into the
object.

reference - An pointer to an object’s location in memory
rather than the actual object

Magic Methods

Methods provided by PHP5 automagically (called by PHP on certain events)

Always begin with __ (two underscores)

Declared public by default but can be overridden

Magic Methods

__construct() __sleep()

__destruct() __wakeup()

__get() __isset()

__set() __unset()

__call() __autoload()

__toString() __clone()

__construct() & __destruct()

__construct() runs when a new object is instantiated.

Suitable for any initialization that the object may need before
it’s used.

__destruct() runs when all references to an object are no
longer needed or when the object is explicitly destroyed.

__get()

__get() is called when trying to access an undeclared
property
<?php
class Car
{

protected $_data = array(
‘door’ => 4,
‘type’ => ‘Jeep’,
‘vin’ => ‘2948ABJDKZLE’
);

public function __get($varName)
{
return $this->_data[$varName];
}
}

$car = new Car();
echo $car->vin; // will print out 2948ABJDKZLE

?>

__set()
__set() is called when trying to assign an undeclared
property

<?php
class Car
{

‘door’ => 4,
);

public function __set($varName, $value)
{
$this->_data[$varName] = $value;
}
}

$car = new Car();
$car->vin = ‘ABC’;
echo $car->vin; // will print out ABC

?>

__isset()
Used to check whether or not a data member has been declared
<?php
class Car
{

‘door’ => 4,
);

public function __isset($varName)
{
return isset($this->_data[$varName]);
}
}

$car = new Car();

if (isset($car->color)) {
echo “color is set!”;
} else {
echo “color isn’t set!”;
}
// will print color isn’t set
?>

__unset()
Removes a data member from a class
<?php
class Car
{

‘door’ => 4,
);

public function __unset($varName)
{
return unset($this->_data[$varName]);
}
}

$car = new Car();
unset($car->vin);

if (isset($car->vin)) {
echo “vin is set!”;
} else {
echo “vin isn’t set!”;
}
// will print vin isn’t set
?>

__call()

__call() is executed when trying to access a method that
doesn’t exist

This allows you to handle unknown functions however you’d
like.

_call() Example
<?php
class Sample
{

public function __call($func, $arguments)
{
echo "Error accessing undefined Method ";
echo "Method Called: " . $func . " ";
echo "Argument passed to the Method: ";
print_r($arguments);
}
}

$sample = new Sample();
echo $sample->doSomeStuff("Test");

?>

__toString()

Returns the string representation of a class

Is automatically called whenever trying to print or echo a
class.

Useful for deﬁning exactly what you want an object to look
like as a string

Can also be used to prevent people from printing the class
without throwing an exception

__toString() Example
<?php
class SqlQuery
{
protected $_table;
protected $_where;
protected $_orderBy;
protected $_limit;

public function __construct($table, $where, $orderBy, $limit)
{
$this->_table = $table;
$this->_where = $where;
$this->_orderBy = $orderBy;
$this->_limit = $limit;
}

public function __toString()
{
$query = “SELECT * “
. “FROM $this->_table “
. “WHERE $this->_where “
. “ORDER BY $this->_orderBy “
. “LIMIT $this->_limit”;

return $query;
}
}

$test = new SqlQuery('tbl_users', “userType = ‘admin’”, ‘name’, 10);
echo $test;

?>

__sleep()

Called while serializing an object

__sleep() lets you deﬁne how you want the object to be
stored

Also allows you to do any clean up you want before
serialization

Used in conjunction with __wakeup()

__wakeup()

The opposite of __sleep() basically

Called when an object is being unserialized

Allows you to restore the class data to its normal form

__clone()

In php setting one object to another
does not copy the original object;
only a reference to the original is
made

To actually get a second copy of the
object, you must use the __clone
method

__clone() example

<?php
class Animal
{
public $color;

public function setColor($color)
{
$this->color = $color;
}

public function __clone()
{
echo " Cloning animal...";
}
}

$tiger = new Animal();
$tiger->color = "Orange";

$unicorn = clone $tiger;
$unicorn->color = "white";

echo " A tiger is " . $tiger->color;
echo " A unicorn is " . $unicorn->color;
?>

__autoload()
Called when you try to load a class in a ﬁle that was not
already included

Allows you to do new myClass() without having to include
myClass.php ﬁrst.

_autoload() example
<?php

class Account
{

public function __autoload($classname)
{
require_once $classname . ‘.php’; //$classname will be Profile
}

public function __construct()
{
$profile = new Profile();
}
}
?>

A little example

You can use all this stuff you just learned about inheritance,
scoping, interfaces, and abstract classes to do some more
complex things!

How Would You Solve This?

I have a bunch of shapes of which I want to ﬁnd the area

I could get any combination of different shapes

I want to be able to ﬁnd the area without having to know
the details of the calculation myself.

What OOP techniques could we use to solve this problem?

Polymorphism is the answer!

...What exactly would you say that is?

Polymorphism

The last object-oriented technique!

Combination of the other techniques

Allowing values of different types to be handled by a uniform
interface

Polymorphism Example!

Polymorphism allows a set of heterogeneous elements to be
treated identically.

Achieved through inheritance

Polymorphism

<?php

interface HasArea
{
public function area();
}
?>

Polymorphism

<?php

abstract class Shape
{
private $_color;

public function __construct($color)
{
$this->_color = $color;
}

public function getColor()
{
return $this->_color;
}
}
?>

Polymorphism
<?php

class Rectangle extends Shape implements HasArea
{
private $_w; // width
private $_h; // height

public function __construct($color, $w, $h)
{
parent::__construct($color);
$this->_w = $w;
$this->_h = $h;
}

public function area()
{
return ($this->_w * $this->_h);
}
}
?>

Polymorphism

<?php

class Circle extends Shape implements HasArea
{
private $_r; // radius

public function __construct($color, $r)
{
parent::__construct($color);
$this->_r = $r;
}

public function area()
{
return (3.14 * pow($this->_r, 2));
}
}
?>

Polymorphism
<?php

// this function will only take a shape that implements HasArea
function getArea(HasArea $shape)
{
return $shape->area();
}

$shapes = array(
'rectangle' => new Rectangle("red", 2, 3),
'circle' => new Circle("orange", 4)
);

foreach ($shapes as $shapeName => $shape) {
$area = getArea($shape);
echo $shapeName . " has an area of " . $area . " ";
}

// will print:
// rectangle has an area of 6
// circle has an area of 50.24
?>

QUESTIONS?

Jason Austin

@jason_austin

jfaustin@gmail.com

http://jasonawesome.com

Object Oriented PHP5

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