An abstract class defines the basic skeleton for the class. It contains attributes and members but
some members are incomplete and is waiting for some other class to extend it through inheritance
so that the derived class provides a full functionality for the incomplete methods. A abstract class
cannot be instantiated and it can only be extended. A class prefix with “abstract” keywords are
abstract class. If a method is defined as abstract then it cannot be declared as private (it can only be
public or protected).
Syntax:
< ?
abstract class classname
{
//attributes and methods
.
.
abstract function methodname
}
class derived extends classname
{
function methodname
}
?>
Example 1 – Basic Abstract Class Usage
< ?
abstract class employee
{
protected $empname;
protected $empage;
function setdata($empname,$empage)
{
$this->empname = $empname;
$this->empage = $empage;
}
abstract function outputData();
}
//extending abstract class
class EmployeeData extends employee
{
function __construct($name,$age)
{
$this->setdata($name,$age);
}
function outputData()
{
echo $this->empname;
echo $this->empage;
}
}
$a = new EmployeeData("Hitesh","24");
$a->outputData();
?>
Output:
Hitesh
24
Explanation for the Example 1:
• Here i have made employee class an abstract class
• Employee class has 2 data members $empname and $empage. It also has a abstract method
outputData() and public method setData()
• Now i am extending the employee class in EmployeeData. It contains the functionality for
the abstract method outputData defined in employee class
Example 2 – Abstract Class Error
< ?
abstract class employee
{
protected $empname;
protected $empage;
function setdata($empname,$empage)
{
$this->empname = $empname;
$this->empage = $empage;
}
abstract function outputData();
}
class EmployeeData extends employee
{
function __construct($name,$age)
{
$this->setdata($name,$age);
}
}
$a = new EmployeeData("Hitesh","24");
$a->outputData();
//Will generate error as the EmployeeData class doesn't has the abstract
method defined
?>
Output
This will give you an error “Class EmployeeData contains 1 abstract method and must therefore be
declared abstract or implement the remaining methods (employee::outputData)”
Example3 – Multiple Abstract Class
< ?
abstract class employee
{
protected $empname;
protected $empage;
function setdata($empname,$empage)
{
$this->empname = $empname;
$this->empage = $empage;
}
abstract function outputData();
}
abstract class EmployeeData extends employee
{
abstract function setDataForEmployee();
}
class Payment extends EmployeeData
{
function setDataForEmployee()
{
//Functionality
}
function outputData()
{
echo "Inside Payment Class";
}
}
$a = new Payment();
$a->outputData();
?>
Output: “Inside Payment Class”
Interface :
This article will guide through the Interface Class in Object Oriented Programming. In simple
words Interface is a class with no data members and contains only member functions and they lack
its implementation. Any class that inherits from an interface must implement the missing member
function body. Interfaces is also an abstract class because abstract class always require an
implementation. In PHP 5 class may inherit only one class, but because interfaces lack an
implementation any number of class can be inherited. In PHP 5, interfaces may declare only
methods. An interface cannot declare any variables. To extend from an Interface, keyword
implements is used. PHP5 supports class extending more than one interface.
Syntax:
interface interfacename
{
function name()
function name1()
}
href='http://www.hiteshagrawal.com/php/oops-in-php5-polymorphism'>Polymorphism
in PHP5
class temp implements interfacename
{
public function name
{
}
}
Example1 – Interface Class in PHP5
< ?
interface employee
{
function setdata($empname,$empage);
function outputData();
}
class Payment implements employee
{
function setdata($empname,$empage)
{
//Functionality
}
function outputData()
{
echo "Inside Payment Class";
}
}
$a = new Payment();
$a->outputData();
?>
Output: “Inside Payment Class”
Explanation for the above Example:
Here i have a interface class called employee having two methods setData() and
outputData()
I am implementing the interface class on Payment class. Payment class also contains the
functionality for the methods defined in the interface.
Example2 – Combining Abstract Class and Interface Class
< ?
interface employee
{
function setdata($empname,$empage);
function outputData();
}
abstract class Payment implements employee //implementing employee interface
{
abstract function PaymentInfo();
}
class PaySlip extends Payment
{
function collectPaySlip()
{
echo "PaySlip Collected";
$this->outputData();
}
function outputData()
{
echo "Inside PaySlip Class";
}
function PaymentInfo()
{
echo "Inside PaySlip Class";
}
function setData($empname,$empage)
{
//Functionality
}
}
$a = new PaySlip();
$a->collectPaySlip();
?>
Output:
PaySlip Collected
Inside Payment Class
Inheritance :
This tutorial will guide you through one of the main feature of Object Oriented Programing which
is called Inheritance. Basically Inheritance is a mechanism where a new class is derived from the
existing base class. The derived class shares/inherit the functionality of the base class. To extend the
class behavior PHP5 have introduced a new keyword called “extends“.
While performing Inheritance operation Access Specifiers specify the level of access that the
outside world (other objects and functions) have on the data members / member functions of the
class. During Inheritance operation the derived class can access the parent class attributes having
protected/public access specifier. To access private data of parent class from derived class you will
have to call public/protected method of the parent class which will access the private variable and
return the data to the derived class. In PHP5 only single inheritance is allowed. i.e. You can inherit
only one class.
Example 1 – Parent Keyword in Inheritance Error
< ?
//Generates an error
class parent
{
private $firstname;
private $lastname;
}
class children extends parent
{
function __construct()
{
echo $this->firstname;
echo $this->lastname;
}
}
$a = new children();
?>
Output: Generate error in PHP5 as parent is keyword in PHP5.
Explanation: Parent is the Keyword in PHP5 and it cannot be used in PHP5 for declaring
classname.
Example 2 – Basic Inheritance Call
< ?
class parent1
{
protected $firstname = 11;
protected $lastname = 23;
}
class children extends parent1
{
function __construct()
{
echo $this->firstname;
echo $this->lastname;
}
}
$a = new children();
?>
Output: 1123
Explanation: Parent1 class have extending its functionality to the children class. Now the children class can access the
$firstname and $lastname attributes.
Example 3 – Accessing Private Data Member through Inheritance
< ?
class parent1
{
private $firstname = "hitesh";
protected $lastname = 23;
protected function getData()
{
return $this->firstname;
}
}
class children extends parent1
{
function __construct()
{
echo $this->getData();
}
}
$a = new children();
?>
Output: hitesh
OOPS in PHP 5 – Polymorphism
Polymorphism in PHP5 is a technique where the function to be called is detected based on the class object calling it at runtime. The basis of Polymorphism is Inheritance and function overridden.
Example – Basic Polymorphism
< ?
class BaseClass
{
public function myMethod()
{
echo "BaseClass method called";
}
}
class DerivedClass extends BaseClass
{
public function myMethod()
{
echo "DerivedClass method called";
}
}
function processClass(BaseClass $c)
{
$c->myMethod();
}
$c = new DerivedClass();
processClass($c);
?>Output: DerivedClass method called
Explanation:
Here i am declaring BaseClass and DerivedClass but i am calling the the processClass with the Derived Class Object.
Encapsulation
Encapsulation is just wrapping some data in an object. The term "encapsulation" is often used interchangeably with "information hiding".
<?php
class App {
private static $_user;
public function User( ) {
if( $this->_user == null ) {
$this->_user = new User();
}
return $this->_user;
}
}
class User {
private $_name;
public function __construct() {
$this->_name = "Joseph Crawford Jr.";
}
public function GetName() {
return $this->_name;
}
}
$app = new App();
echo $app->User()->GetName();
?>
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