Tag Archives: OOPS

Abstract Classes

PHP 5 introduces abstract classes and methods. Classes defined as abstract may not be instantiated, and any class that contains at least one abstract method must also be abstract. Methods defined as abstract simply declare the method’s signature – they cannot define the implementation.

When inheriting from an abstract class, all methods marked abstract in the parent’s class declaration must be defined by the child; additionally, these methods must be defined with the same (or a less restricted) visibility. For example, if the abstract method is defined as protected, the function implementation must be defined as either protected or public, but not private. Furthermore the signatures of the methods must match, i.e. the type hints and the number of required arguments must be the same. For example, if the child class defines an optional argument, where the abstract method’s signature does not, there is no conflict in the signature.

Constructor

A is special method of the class that will be automatically invoked when an instance of the class is created is called as constructor.

Constructors are mainly used to initialize private fields of the class while creating an instance for the class.

When you are not creating a constructor in the class, then compiler will automatically create a default constructor in the class that initializes all numeric fields in the class to zero and all string and object fields to null.

Types of Constructors

  • Default Constructor
  • Parameterized Constructor
  • Copy Constructor
  • Static Constructor
  • Private Constructor

Abstract Class vs Interface

1) For abstract class a method must be declared as abstract. Abstract methods doesn’t have any implementation.
For interface all the methods by default are abstract methods only. So one cannot declare variables or concrete methods in interfaces.

2) The Abstract methods can declare with Access modifiers like public, internal, protected. When implementing in subclass these methods must be defined with the same (or a less restricted) visibility.
All methods declared in an interface must be public.

3)Abstract class can contain variables and concrete methods.Interfaces cannot contain variables and concrete methods except constants.

4)A class can Inherit only one Abstract class and Multiple inheritance is not possible for Abstract class.
A class can implement many interfaces and Multiple interface inheritance is possible.

 

Difference Between abstract class and interface PHP

1) For abstract class a method must be declared as abstract. Abstract methods doesn’t have any implementation.
For interface all the methods by default are abstract methods only. So one cannot declare variables or concrete methods in interfaces.

2) The Abstract methods can declare with Access modifiers like public, internal, protected. When implementing in subclass these methods must be defined with the same (or a less restricted) visibility.
All methods declared in an interface must be public.

3)Abstract class can contain variables and concrete methods.Interfaces cannot contain variables and concrete methods except constants.

4)A class can Inherit only one Abstract class and Multiple inheritance is not possible for Abstract class.
A class can implement many interfaces and Multiple interface inheritance is possible.

 

Factory Classes

Factory classes provide an interface for creating families of related objects. Factory classes are useful when the decision of which class to use must be done at run time and cannot be hard coded during development. Factory classes encapsulate the logic needed to decide which subclass to instantiate and so removes this decision from the application, delegating it to the factory.

 

Class

A class is used to specify the form of an object and it combines data representation and methods for manipulating that data into one neat package. The data and functions within a class are called members of the class.

Use classes to encapsulate code and represent objects, and namespaces to avoid symbol name collisions

A. A class can not extend more than one class.

B. A class can not implement more than one class.

C. A class cannot extend more than one interface.

D. A class can implement more than one interface.

Example

<?php
 class a{
 function function_a(){
 echo "Function A";
 }
 }

a::function_a();
 ?>

Data encapsulation

Encapsulation is an Object Oriented Programming concept that binds together the data and functions that manipulate the data, and that keeps both safe from outside interference and misuse. Data encapsulation led to the important OOP concept of data hiding.

Data encapsulation is a mechanism of bundling the data, and the functions that use

Implements

We use implements keyword to extend interface of class, at the same time we can implement more than one interface and one interface can be implemented by another interface.

All methods declared in an interface must be public and the variables should be constant.

This is mandatory that we must declare the body part of the method in the derived class otherwise an error message will be generated.

Example

<?php
interface a{
public function test();
}

class b implements a{
public function test(){
echo “Function Test”;
}
}

$b=new b();
$b->test();
?>