To better understand the behavior of servlets, let’s take a look at the life cycle of servlets. A servlet is basically a small Java program that runs within a Web server. It can receive requests from clients and return responses. The whole life cycle of a servlet breaks up into 3 phases: • Initialization: A servlet is first loaded and initialized usually when it is requested by the corresponding clients. Some websites allow the users to load and initialize servlets when the server is started up so that the first request will get responded more quickly. • Service: After initialization, the servlets serve clients on request, implementing the ap- plication logic of the web application they belong to. • Destruction: When all pending requests are processed and the servlets have been idle for a specific amount of time, they may be destroyed by the server and release all the resources they occupy. More specifically, the behavior of a servlet is described in javax.servlet.Servlet interface, in which the following methods are defined: • public void init(ServletConfig config) throws ServletException This method is called once when the servlet is loaded into the servlet engine, before the servlet is asked to process its first request. The init method has a ServletConfig parameter. The servlet can read its initialization arguments through the ServletConfig object. How the initialization arguments are set is servlet engine dependent but they are usually defined in a configuration file. A typical example of an initialization argument is a database identifier. A servlet can read this argument from the ServletConfig at initialization and then use it later to open a connection to the database during processing of a request: private String databaseURL; public void init(ServletConfig config) throws ServletException { super.init(config); databaseURL = config.getInitParameter("database"); } • public void service(ServletRequest request, ServletResponse response) throws ServletException, IOException This method is called to process a request. It can be called zero, one or many times until the servlet is unloaded. Once a servlet is loaded, it remains in the server’s memory as a single object instance. Thereafter, the server invokes the servlet to handle a request using a simple, lightweight method invocation. Unlike with CGI, there’s no process to spawn or interpreter to invoke, so the servlet can begin handling the request almost immediately. Multiple, concurrent requests are handled by separate threads, so servlets are highly scalable. Servlets are naturally enduring objects. Because a servlet stays in the server’s memory as a single object instance, it automatically maintains its state and can hold on to external resources, such as database connections, that may otherwise take several seconds to establish. The following servlet presents information about how many times it has been accessed: To better understand the behavior of servlets, let’s take a lo

1. OOPS IN PHP
By
Dr M.RANI REDDY

2. Topics
What is OOPS
Class & Objects
Modifier
Constructor
Deconstructor
Class Constants
Inheritance In Php
Magic Function
Polymorphism
Interfaces
Abstract Classes
Static Methods And Properties
Accessor Methods
Determining A Object's Class

3. What Is Oop ?
Object Oriented Programming (OOP) is the
programming method that involves the use of
the data , structure and organize classes of an
application. The data structure becomes an
objects that includes both functions and data. A
relationship between one object and other
object is created by the programmer

4. Classes
A class is a programmer
defined datatype which
include local fuctions as well
as local data.
Like a pattern or a blueprint
a oops class has exact
specifications. The
specification is the class' s
contract.

5. Creating a class
<?php
Class emailer
{
Private $sender;
Private $receiver;
}

6. An object is a like a container that
contains methods and properties
which are require to make a certain
data types useful. An object’s
methods are what it can do and its
properties are what it knows.
Object

7. Modifier
In object oriented programming, some
Keywords are private and some are public in
class. These keyword are known as modifier.
These keywords help you to define how these
variables and properties will be accessed by the
user of this class.

8. Modifier
Private: Properties or methods declared as
private are not allowed to be called from
outside the class. However any method inside
the same class can access them without a
problem. In our Emailer class we have all these
properties declared as private, so if we execute
the following code we will find an error.

9. Modifier
<?
include_once("class.emailer.php");
$emobject = new Emailer("mranimca@rediff.com");
$emobject->subject = "Hello world";
?>
The above code upon execution gives a fatal error as shown below:
<b>Faprivate property emailer::$subject
in <b>C:OOP with PHP5Codesch1class.emailer.php</b> on line
<b>43</><br />
tal error</b>: Cannot access That means you can't access

10. Modifier
Public: Any property or method which is not
explicitly declared as private or protected is a
public method. You can access a public method
from inside or outside the class.
Protected: This is another modifier which has a
special meaning in OOP. If any property or
method is declared as protected, you can only
access the method from its subclass. To see
how a protected method or property actually
works, we'll use the following example:

11. Modifier
To start, let's open class.emailer.php file (the
Emailer class) and change the declaration of the
$sender variable. Make it as follows:
protected $sender
Now create another file name
class.extendedemailer.php with the following
code:

12. Modifier
<?
class ExtendedEmailer extends emailer
{
function construct(){}
public function setSender($sender)
{
$this->sender = $sender;
}
}
?>

13. Constructor & Destructor
Constructor is Acclimated to Initialize the
Object.
Arguments can be taken by constructor.
A class name has same name as Constructor.
Memory allocation is done by Constructor

14. Constructor & Destructor
The objects that are created in memory, are
destroyed by the destructor.
Arguments can be taken by the destructor.
Overloading is possible in destructor.
It has same name as class name with tiled operator.

15. Class
Contants

16. Class Constants
You can make constants in your PHP scripts
utilizing the predefine keyword to define
(constant name, constant value). At the same
time to make constants in the class you need to
utilize the const keyword. These constants
really work like static variables, the main
distinction is that they are read-only.

17. Class Constants
<?
class WordCounter
{
const ASC=1; //you need not use $ sign before Constants
const DESC=2;
private $words;
function construct($filename)
{
$file_content = file_get_contents($filename);
$this->words =
(array_count_values(str_word_count(strtolower
($file_content),1)));

18. Class Constants
}
public function count($order)
{
if ($order==self::ASC)
asort($this->words);
else if($order==self::DESC)
arsort($this->words);
foreach ($this->words as $key=>$val)
echo $key ." = ". $val."<br/>";
}
}
?>

19. Inheritance

20. Inheritance In Php
Inheritance is a well-known programming rule,
and PHP makes utilization of this standard in its
object model. This standard will influence the
way numerous objects and classes identify with
each other.
For illustration, when you extend a class, the
subclass inherits each public and protected
method from the guardian class. Unless a class
overrides those techniques, they will hold their
unique functionality

21. Inheritance

22. Magic Functions
There are some predefine function names
which you can’t use in your programme unless
you have magic functionality relate with them.
These functions are known as Magic Functions.
Magic functions have special names which
begine with two underscores.

23. Magic Functions
_ _construct()
_ _deconstruct()
_ _call()
_ _callStatic()
_ _get()
_ _set()
_ _isset()
_ _unset()
sleep()
wakeup()
tostring()
invoke()
set_state()
clone()
debugInfo()

24. Magic Functions
_ _construct()
Construct function is called when object is
instantiated. Generally it is used in php 5 for
creating constructor
_ _deconstruct()
It is the opposite of construct function. When
object of a class is unset, this function is called.

25. Magic Functions
_ _call()
When a class in a function is try to call an
accessible or inaccessible function , this method
is called.
_ _callStatic()
It is similar to callStatic() with only one
difference that is its triggered when you try to
call an accessible or inaccessible function in
static context.

26. Magic Functions
_ _get()
This function is triggered when your object try
call a variable of a class which is either
unavailable or inaccessible.
_ _set()
This function is called when we try to change to
value of a property which is unavailable or
inaccessible.

27. Polymorphism

28. Polymorphism
The ability of a object, variable or function to
appear in many form is known as
polymorphism. It allows a developer to
programme in general rather than programme
in specific. There are two types of
polymorphism.
compile time polymorphism
run-time polymorphism".

29. Interfaces
There are some specific set of variable and functions
which can be called outside a class itself. These are
known as interfaces. Interfaces are declared using
interface keyword.
<?
//interface.dbdriver.php
interface DBDriver
{
public function connect();
public function execute($sql);
}
?>

30. Abstract Classes

31. Abstract Classes
A class which is declared using abstract keyword is
known as abstract class. An abstract class is not
implemented just declared only (followed by
semicolon without braces)
<?
//abstract.reportgenerator.php
abstract class ReportGenerator
{
public function generateReport($resultArray)
{
//write code to process the multidimensional result array and
//generate HTML Report
}
}
?

32. Static Method And
Properties

33. Static Methods & Properties
In object oriented programming, static keyword is
very crucial. Static properties and method acts as a
significant element in design pattern and application
design. To access any method or attribute in a class
you must create an instance (i.e. using new keyword,
like $object = new emailer()), otherwise you can't
access them. But there is a difference for static
methods and properties. You can access a static
method or property directly without creating any
instance of that class. A static member is like a global
member for that class and all instances of that class

34. Static Methods & Properties
<?
//class.dbmanager.php
class DBManager
{
public static function getMySQLDriver()
{
//instantiate a new MySQL Driver object and return
}
public static function getPostgreSQLDriver()

35. Static Methods & Properties
{
//instantiate a new PostgreSQL Driver object and
return
}
public static function getSQLiteDriver()
{
//instantiate a new MySQL Driver object and return
}
}
?>

36. Accessor Method
Accessor methods are simply methods that are
solely devoted to get and set the value of any class
properties. It's a good practice to access class
properties using accessor methods instead of
directly setting or getting their value. Though
accessor methods are the same as other methods,
there are some conventions writing them. There
are two types of accessor methods. One is called
getter, whose purpose is returning value of any
class property. The other is setter that sets a value
into a class property.

37. Accessor Method
<?
class Student
{
private $name;
private $roll;
More free ebooks : http://fast-file.blogspot.com
Chapter 2
[ 39 ]
public function setName($name)
{
$this->name= $name;
}

38. Accessor Method
public function setRoll($roll)
{
$this->roll =$roll;
}
public function getName()
{
return $this->name;
}
public function getRoll()
{
return $this->roll;
}
}
?>

39. Determining A Object's Class
public function setRoll($roll)
{
$this->roll =$roll;
}
public function getName()
{
return $this->name;
}
public function getRoll()
{
return $this->roll;
}
}
?>