Abstract classes and Interface are very important concept in object oriented programming in PHP.

In this section we will look on following topics:

·         What is abstract class?

·         How to implement abstract class?

·         What is interface?

·         How to implement interface?

·         Difference between abstract class and interface

What is abstract class? 

Abstract classes are those classes which cannot be instantiated and require subclasses to provide implementation for the abstract methods or in other words you cannot create object of abstract classes and these classes are used for inheritance purpose. Abstract classes can only inherited in your child class.

An abstract class may contain one or more abstract method, but in PHP it may or may not contain abstract methods.  Class Abstraction is a way to inherit another class to implement specific methods. In other words, when we extend any abstract class (parent class), all the methods in parent’s class must be defined by child class.

The parent class is called abstract class and the child class which is called as a concrete class. So, parent class force concrete class to implement specific methods and these methods are called abstract methods.

 Some points to be remember

·    If any class that has one abstract method, is termed as abstract class.

·    An abstract class cannot be instantiated, you must instantiate child class or concrete class.

·    An abstract method does not implement the method they only provide the abstract for the child class to implement.

How to implement abstract class?

You can create abstract class using keyword abstract in PHP. Once you have created abstract class then you cannot create object of that abstract class. Let’s see an example in which you have created the object of an abstract class:

<?php
abstract class test
{
public function abc()
{
return 1;
}
}
$obj = new test(); // Code will throw fatal error.

?>

<?php
abstract class My_parent
{
abstract public function text();
}
class Child extends My_parent
{
public function text()
{
echo "Hello World!! I am child class";
}
}
$obj = new Child();
$obj->text();

?>

<?php
interface test
{
public function abc($a); // visibility should always be public
}
?>

<?php
interface test
{
public function abc($a);
}
class child implements test
{
public function abc($a)
{
//your function body
}
}
?>

<?php
interface AName{
public function Add();
} 
interface SName{
function Sub();
} 
class CName implements AName,SName
{
public function Add()
{ 
$x = 5;
$x = $x + 1;
echo "The answer of Add function:".$x ."</br>";
}
function Sub()
{ 
$y=10;
$z=5;
$c = $y -$z;
echo "The answer of Sub function:".$c;
}
}
$obj= new CName();
$obj->Add();
$obj->Sub();
?>