Lecture 17 - PHP-Object-Orientation.pptx

http://xkcd.com/327/
Remember our last lecture?

Encapsulation, Inheritance, Polymorphism

Object Orientation
 PHP is an Object-Oriented programming
language
 Fundamental feature of OO is the class
 PHP classes support
 Encapsulation
 Inheritance
 Polymorphism

What is a Class?
Classes
 Sophisticated ‘variable types’
 Data variables (data members) and functions
(methods) are wrapped up in a class. Collectively,
data members and methods are referred to as class
members.
An instance of a class is known as an object.
//defining a new class named Robot
class Robot {
//place class members here...
}

Instantiating a class using new
 Once a class has been created, any number of
object instances of that class can be created.
 $dogRobot = new Robot();
 To invoke methods:
 object->method()
 e.g.
<?php
....
$dogRobot = new Robot();
$dogRobot ->crawlWeb();
$dogRobot -> play();
echo $dogRobot ->talk();
...
?>

<?php
class Person {
private $strFirstname = “Napoleon";
private $strSurname = “Reyes";
function getFirstname() {
return $this->strFirstname;
}
function getSurname() {
return $this->strSurname;
}
}
// outside the class definition
$obj = new Person; // an object of type Person
echo "Firstname: " . $obj->getFirstname() . "";
echo "Surname: " . $obj->getSurname() . "";
?>
Defining classes
Data members
Methods
Example16-1.php

Encapsulation
Data members are normally set inaccessible from outside
the class (as well as certain types of methods) protecting
them from the rest of the script and other classes.
This protection of class members is known as
encapsulation.
 e.g.
<?php
....
$dogRobot = new Robot();
$dogRobot ->crawlWeb();
$dogRobot -> play();
echo $dogRobot ->talk();
...
?>

Inheritance
New classes can be defined very similar to existing ones.
All we need to do is specify the differences between the
new class and the existing one.
Data members and methods which are not defined as
being private to a class are automatically accessible by
the new class.
This is known as inheritance and is an extremely powerful
and useful programming tool.

Polymorphism
A concept where a number of related classes all have a
method, which shares the same name.
class Fish { draw()... //draws a fish... }
class Dog { draw()... //draws a dog... }
class Bird { draw()... //draws a bird... }
We can write a generic code that can operate on any of
these classes, invoking the appropriate draw() method
based on certain conditions.

Example: Defining classes
class ShoppingCart {
private $name; // Name of shopper
private $items; // Items in our shopping cart
public function ShoppingCart($inputname) {
$this->name = $inputname;
}
// Add $num articles of $artnr to the cart
public function addItem($artnr, $num) {
$this->items[$artnr] += $num;
}
// Take $num articles of $artnr out of the cart
public function removeItem($artnr, $num) {
if ($this->items[$artnr] > $num) {
$this->items[$artnr] -= $num;
return true;
} elseif ($this->items[$artnr] == $num) {
unset($this->items[$artnr]);
return true;
} else {
return false;
}
}
}
Let’s examine the syntax of defining a class next...

Data members and Methods
class Class1 {
private $strName = “A”;
private $intNumber = 1;
function getName() {
}
function getNumber(){
}
}
 We need to provide
accessor functions to
allow users of Class1
to access the private
data members:
function getName(){
return $this->strName;
}
Is this publicly accessible?

$this object pointer
 As with so many languages, there is a special
pointer that references an instance of a class:
 $this
function getName(){
return $this->strName;
}
function getName(){
return strName;
}
 

Invoking methods inside a class
class Person{
...
function setFirstname($strSurname) {
$this->strFirstname = $strSurname;
}
function setSurname($strSurname) {
$this->strSurname = $strSurname;
}
private function display() {
echo "Firstname: " . $this->strFirstname . "";
echo "Surname: " . $this->strSurname . "";
}
function setDisplayFirstnameSurname($strFirstname, $strSurname) {
$this->setFirstname($strFirstname);
$this->setSurname($strSurname);
$this->display();
}
}
$this->functionName();
Example16-4.php

Classes
class MyClassName{
....methods
....data members
}
 Visibility of a method
or data member:
 Public
 Protected
 Private
 By default, without
the access specifiers,
class members are
defined public.

Private Access Specifier
class MyClassName{
private $strFirstName;
}
 private – limits the
visibility of the methods
and data members only
to the class that defines
them.

Modifying data members
 Outside the class, trying to execute
the following:
$clMyObj->intNumber++;
 will fail!...
 We need a method to access and change its
value:
function setNumber($intNumber) {
$this->intNumber = $intNumber;
}
 intNumber is private
Look at the position of the dollar sign ($) – no
longer attached to the variable name

Public Access Specifier
class MyClassName{
public $strFirstName;
public function getFirstName(){
}
}  public – class
members can be
accessed both within
and outside the
class.

Protected Access Specifier
Class MyClassName{
protected $strFirstName;
protected function getFirstName(){
}
}
 Inherited protected class members –
accessible inside a derived class
 Visibility of protected class
members outside the class definition
– protected class members are
inaccessible.
//protected for public use, but accessible in a
derived class

<?php
class MyClass {
public $public = 'Public';
protected $protected = 'Protected'; //protected for public use, but accessible in a derived class
private $private = 'Private';
function printHello() {
echo $this->public;
echo $this->protected;
echo $this->private;
}
}
$obj = new MyClass();
echo $obj->public; // Works
echo $obj->protected; // Fatal Error
echo $obj->private; // Fatal Error
$obj->printHello(); // Shows Public, Protected and Private
//...
Example: Access Specifiers




http://php.net/manual/en/language.oop5.visibility.php

<?php
//...
class MyClass2 extends MyClass
{
// We can redeclare the public and protected method, but not private
// protected – ‘protected’ for public use, but accessible in a derived class
protected $protected = 'Protected2';
function printHello()
{
echo $this->public;
echo $this->protected;
echo $this->private;
}
}
$obj2 = new MyClass2();
echo $obj2->public; // Works
echo $obj2->private; // Undefined
echo $obj2->protected; // Fatal Error
$obj2->printHello(); // Shows Public, Protected2, Undefined
?>
Example: Access Specifiers




a Derived class

//OUTSIDE THE CLASS DEFINITION...
$myclass = new MyClass;
$myclass->MyPublic(); // Works
$myclass->MyProtected(); // Fatal Error
$myclass->MyPrivate(); // Fatal Error
$myclass->Foo(); // Public, Protected and Private work
//...
<?php
class MyClass
{
// Declare a public constructor
public function __construct() { }
// Declare a public method
public function MyPublic() { }
// Declare a protected method
protected function MyProtected() { }
// Declare a private method
private function MyPrivate() { }
// This is public
function Foo()
{
$this->MyPublic();
$this->MyProtected();
$this->MyPrivate();
}
}




Example: Method Declaration

class MyClass2 extends MyClass
{
// This is public
function Foo2()
{
$this->MyPublic();
$this->MyPrivate(); // Fatal Error
}
}
$myclass2 = new MyClass2;
$myclass2->MyPublic(); // Works
$myclass2->Foo2(); // Public and Protected work, not Private
  
<?php
class MyClass
{
// Declare a public constructor
public function __construct() { }
// Declare a public method
public function MyPublic() { }
// Declare a protected method
protected function MyProtected() { }
// Declare a private method
private function MyPrivate() { }
// This is public
function Foo()
{
$this->MyPublic();
$this->MyPrivate();
}
}

$myFoo = new foo();
$myFoo->test(); // Bar::testPrivate
// Foo::testPublic
?>


<?php
class Bar
{
public function test() {
$this->testPrivate();
$this->testPublic();
}
public function testPublic() {
echo "Bar::testPublicn";
}
private function testPrivate() {
echo "Bar::testPrivaten";
}
}
class Foo extends Bar
{
public function testPublic() {
echo "Foo::testPublicn";
}
private function testPrivate() {
echo "Foo::testPrivaten";
}
}

string(5) "hello"
Accessed the private method
Accessing Private Members of
the same object type

<?php
class Test
{
private $foo;
public function __construct($foo)
{
$this->foo = $foo;
}
private function bar()
{
echo 'Accessed the private method.';
}
public function baz(Test $other)
{
// We can change the private property:
$other->foo = 'hello';
var_dump($other->foo);
// We can also call the private method:
$other->bar();
}
}
$test = new Test('test');
$test->baz(new Test('other'));
?>
Objects of the same type will have access to each others
Private and protected members even though they are
not the same instances.

Creating objects
•Instantiate classes using new keyword
–$myCart= new ShoppingCart(“Charlie”);
Constructors
–In earlier versions of PHP (< PHP5.3.3) Same as the
name of the class. This no longer holds!
– (PHP5 only) declared as
• public function __construct(…)
Destructors
–Declared as
–public function __destruct()

Latest in PHP5.3.3
<?php
namespace Foo;
class Bar {
public function Bar() {
// treated as constructor in PHP 5.3.0-5.3.2
// treated as regular method in PHP 5.3.3
}
}
?>
22 Sept. 2010

Constructors
 A constructor is a function that does
initializations when the class is instantiated
function __construct($intNumber, $strName){
$this->set_intNumber($intNumber);
$this->set_strName($strName);
$this->printInit();//use this method
}

Constructors
 Default arguments
function __construct ($strName = “A”, $intNumber=0) {
$this->set_intNumber($int_Number);
$this->set_strName($str_Name);
}
 Instantiating a class without parameters will
make use of the default values

Another Example: Constructors
<?php
class vehicle {
private $strDescription;
function getDescription() {
return $this->strDescription;
}
function setDescription($strDescription) {
$this->strDescription = $strDescription;
}
function __construct ($strDescription) {
$this->strDescription = $strDescription;
}
}
?>
vehicle.php

Another Example: Constructors
<?php
require_once("vehicle.php");
$objBike = new vehicle("Bicycle");
echo "Vehicle: " . $objBike->getDescription() . "";
?>
example16-7.php

Destructors
 Called when objects are destroyed – free up
memory
 e.g.:
function __destruct () {
echo “freeing up memory, destroying this object... ”;
}
This sample code above simply informs us that the object is
being destroyed already.

Objects as variables
 Can be used in arrays
 Can be passed to functions
 Passed as reference all the time (PHP 5)
 e.g.:
function test1($objClass1){
$objClass1->set_intName(“B”);
}
 No need to use & in the formal parameter
definition. It is always passed by reference.

Arrays and objects
<?php
function __autoload($class_name) {
require_once $class_name . '.php';
}
$objSimon = new revisedperson("Simon", "Stobart");
$objLiz = new revisedperson("Liz", "Hall");
$objIan = new revisedperson("Ian", "Walker");
$objBilly = new revisedperson("Billy", "Lee");
$objHayley = new revisedperson("Hayley", "West");
$arrPeople = array($objSimon, $objLiz, $objIan, $objBilly, $objHayley);
foreach($arrPeople as $objThePerson){
echo($objThePerson->display());
}
?>
The function display() is common to all array elements
(elements = objects in this example).
example16-9.php

Multiple Object Instances
<?php
$cart1 = new ShoppingCart(“Joe Bloggs”);
$cart1->addItem("10", 1);
$cart2 = new ShoppingCart(“Fred Smith”);
$cart2->addItem("0815", 3);
?>

Example: Polymorphism
<?php
}
$objRectangle = new rectangle(100,50, "rectangle.gif");
$objSquare = new square(100, "square.gif");
$objTriangle = new triangle(50,100, "triangle.gif");
$objEllipse = new ellipse(50,100, "ellipse.gif");
$arrShapes = array ($objRectangle,$objSquare,$objTriangle,$objEllipse);
foreach ($arrShapes as $objShape){
$objShape->display();
$objShape->area();
}
?>
The functions area() and display() are common to all array
elements, but executes a different formula for each type of object.
Example17-5.php

• Recommended: Create one PHP
source file per class definition.
• This aids class reuse and script clarity.

Remember these PHP Constructs?
• require(….)
 Includes file specified, terminates on errors
• include(…)
 Includes file specified, gives warning on errors
• require_once(….)
 Includes file specified only if it has not already been
included, terminates on errors
• include_once(….)
 Includes file specified only if it has not already been
included, gives warning on errors
Example16-6.php

Really useful but would require you to write a long list of include() or require() statements
at the beginning of each script, one for each class. In PHP5, this is no longer
necessary. You may define an __autoload function!

function __autoload()
• The function is invoked automatically each time a class is
required but has not been defined.
• We can insert this function into our script:
Example16-7.php
}
Note: Class_name = File_name

function __autoload()
Example16-7.php
<?php
}
$objSimon = new person;
$objSimon->setDisplayFirstnameSurname(“Napoleon", “Reyes");
$objBike = new vehicle("Bicycle");
echo "Vehicle: " . $objBike->getDescription() . "";
?>
Class definition comes from
another file.

Exceptions
Like all good OO languages, PHP5 supports the exception
mechanism for trapping and handling “unexpected conditions”
Note: not all exceptions are necessarily errors
Exceptions not supported in PHP4

class MyException extends Exception {
// Redefine the exception so message isn't
optional
public function __construct($message, $code = 0) {
// some code
// make sure everything is assigned properly
parent::__construct($message, $code);
}
// custom string representation of object
public function __toString() {
return __CLASS__ . ": $this->messagen";
}
public function customFunction() {
echo "A Custom function for this type of exceptionn";
}
}
Extend the built-in PHP Exception class with your own
exceptions (as in Java)
Exceptions
<?php
Throw new MyException("Message to display");
?>
To generate an exception

Objects can...
 Invoke another
 Be embedded within another object
 Support for:
 Inheritance
 Scope resolution ( :: operator)
 Class abstraction (define a class that does not
instantiate, use “abstract class classname”)
 Polymorphism (same function names with different data
/ behaviour)
 '==‘ to check if two object have the same attributes and values
 '===‘ to check if two objects are the same instance of the same class

Advanced OO in PHP
 PHP5 has rich OO support (similar to the Java model)
 Single inheritance (multiple inheritance not allowed)
 Abstract classes and methods
 Interfaces
 PHP is a reflective programming language
 Names of functions/classes to be invoked do not have to be hard
wired
 See also documentation at www.php.net

Reflection-Oriented Programming
// without reflection
$Foo = new Foo();
$Foo->hello();
// with reflection
$f = new ReflectionClass("Foo");
$m = $f->getMethod("hello");
$m->invoke( $f->newInstance() );
Normally, instructions are
executed and data is
processed; however, in some
languages, programs can
also treat instructions as
data and therefore make
reflective modifications.
http://en.wikipedia.org/wiki/Reflection_(computer_science)
Program execution could be
modified at run-time.
New in PHP, not properly
documented yet!
http://nz2.php.net/manual/en/reflectionclass.newinstance.php

For a complete reference
http://www.php.net

Lecture 17 - PHP-Object-Orientation.pptx

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