Object-oriented programming (OOP) is a technique to
develop logical modules such as classes that contain properties methods fields
and events. An object is created in the program to represent a class.
Therefore, an object encapsulates all the features such as data and behavior
that are associated to a class
Object means a real word entity such as pen, chair, table
etc.
Object-Oriented Programming is a methodology or paradigm
to design a program using classes and objects.
It simplifies the software development and maintenance by
providing some concepts:
- Class
- Object
- Methods
- Inheritance
- Polymorphism
- Abstraction
- Encapsulation
Class
A class is a construct that enables you to create your
own custom types by grouping together variables of other types, methods and
events.
A class is like a blueprint. It defines the data and behavior of a type.
A class is the core of any modern Object Oriented Programming language such as C#.
A class is like a blueprint. It defines the data and behavior of a type.
A class is the core of any modern Object Oriented Programming language such as C#.
In OOP languages it is mandatory to create a class for
representing data.
A class will not occupy any memory space and hence it is
only a logical representation of data.
Syntax
of creating a class
class <ClassName>
{
//Methods
//Properties
}
Example
Class Test
{
Int a ;
String s;
Public Void Sample
{
Console.Write(“Welcome to Complete
.Net Tutorial”);
}
}
Object
An object is basically a block of memory that has been
allocated and configured according to the blueprint.
A program may
create many objects of the same class. Objects are also called instances, and
they can be stored in either a named variable or in an array or collection.
How
To create object for class ?
Test obj ; // it’s a creation of reference variable
to the class it will not store any
memory in heap area.
obj =new Test(); // it is called as an instance of an
object.
Methods
Methods is a member of class which we will use to define same functionality.
Methods is an action that has to be performed.
Methods can be either a returning value or non-value returning also
Syntax
[<modifiers>]void/type <name>([<parameter definitions>])
{
//statements
}
Modifiers
Modifiers are used to modify declarations of types and type members. This section introduces the C# modifiers.
Void
When used as the return type for a method, void specifies that the method doesn't return a value.
void isn't allowed in the parameter list of a method. A method that takes no parameters and returns no value is declared as follows:
public void SampleMethod()
{
// Body of the method.
}
void is also used in an unsafe context to declare a pointer to an unknown type.
Encapsulation:
Encapsulation is a process of binding the data members and member functions into a single unit.
Example for encapsulation is class.
A class can contain data structures and methods.
Consider the following class
public class Aperture
{
public Aperture ()
{
}
protected double height;
protected double width;
protected double thickness;
public double get volume()
{
Double volume=height * width * thickness;
if (volume<0)
return 0;
return volume;
}
}
In this example we encapsulate some data such as height, width, thickness and method Get Volume. Other methods or objects can interact with this object through methods that have public access modifier
Abstraction:
Abstraction is a process of hiding the implementation details and displaying the essential features.
Example1: A Laptop consists of many things such as processor, motherboard, RAM, keyboard, LCD screen, wireless antenna, web camera, usb ports, battery, speakers etc. To use it, you don't need to know how internally LCD screens, keyboard, web camera, battery, wireless antenna, speaker’s works. You just need to know how to operate the laptop by switching it on. Think about if you would have to call to the engineer who knows all internal details of the laptop before operating it. This would have highly expensive as well as not easy to use everywhere by everyone.
So here the Laptop is an object that is designed to hide its complexity.
How to abstract: - By using Access Specifiers
.Net has five access Specifiers
Public -- Accessible outside the class through object reference.
Private -- Accessible inside the class only through member functions.
Protected -- Just like private but Accessible in derived classes also through member
functions.
Internal -- Visible inside the assembly. Accessible through objects.
Protected Internal -- Visible inside the assembly through objects and in derived classes outside the assembly through member functions.
Let’s try to understand by a practical example:-
public class Class1
In object-oriented software, complexity is managed by using abstraction.
Abstraction is a process that involves identifying the critical behavior of an object and eliminating irrelevant and complex details.
Inheritance:
Inheritance is a process of deriving the new class from already existing class
C# is a complete object oriented programming language. Inheritance is one of the primary concepts of object-oriented programming. It allows you to reuse existing code. Through effective use of inheritance, you can save lot of time in your programming and also reduce errors, which in turn will increase the quality of work and productivity. A simple example to understand inheritance in C#.
Using System;
In the Main () method in ChildClass we create an instance of childclass. Then we call the write () method. If you observe the ChildClass does not have a write() method in it. This write () method has been inherited from the parent BaseClass.
The output of the above program is
Output:
Base Class Constructor executed
Child Class Constructor executed
Write method in Base Class executed
this output proves that when we create an instance of a child class, the base class constructor will automatically be called before the child class constructor. So in general Base classes are automatically instantiated before derived classes.
In C# the syntax for specifying BaseClass and ChildClass relationship is shown below. The base class is specified by adding a colon, ":", after the derived class identifier and then specifying the base class name.
Syntax: class ChildClassName: BaseClass
{
//Body
}
C# supports single class inheritance only. What this means is, your class can inherit from only one base class at a time. In the code snippet below, class C is trying to inherit from Class A and B at the same time. This is not allowed in C#. This will lead to a compile time
error: Class 'C' cannot have multiple base classes: 'A' and 'B'.
public class A
{
}
public class B
{
}
public class C : A, B
{
}
In C# Multi-Level inheritance is possible. Code snippet below demonstrates mlti-level inheritance. Class B is derived from Class A. Class C is derived from Class B. So class C, will have access to all members present in both Class A and Class B. As a result of multi-level inheritance Class has access to A_Method(),B_Method() and C_Method().
Note: Classes can inherit from multiple interfaces at the same time. Interview Question: How can you implement multiple inheritance in C#? Ans : Using Interfaces.
Using System;
When you derive a class from a base class, the derived class will inherit all members of the base class except constructors. In the code snippet below class B will inherit both M1 and M2 from Class A, but you cannot access M2 because of the private access modifier. Class members declared with a private access modifier can be accessed only with in the class. We will talk about access modifiers in our later article.
Common Interview Question: Are private class members inherited to the derived class?
Ans: Yes, the private members are also inherited in the derived class but we will not be able to access them. Trying to access a private base class member in the derived class will report a compile time error.
Method Hiding and Inheritance We will look at an example of how to hide a method in C#. The Parent class has a write () method which is available to the child class. In the child class I have created a new write () method. So, now if I create an instance of child class and call the write () method, the child class write () method will be called. The child class is hiding the base class write () method. This is called method hiding.
If we want to call the parent class write () method, we would have to type cast the child object to Parent type and then call the write () method as shown in the code snippet below.
Using System;
Polymorphism:
When a message can be processed in different ways is called polymorphism. Polymorphism means many forms.
Polymorphism is one of the fundamental concepts of OOP.
Polymorphism provides following features:
It allows you to invoke methods of derived class through base class reference during runtime.
It has the ability for classes to provide different implementations of methods that are called through the same name.
Polymorphism is of two types:
Compile time polymorphism/Overloading
Runtime polymorphism/Overriding
Compile Time Polymorphism
Compile time polymorphism is method and operators overloading. It is also called early binding.
In method overloading method performs the different task at the different input parameters.
Runtime Time Polymorphism
Runtime time polymorphism is done using inheritance and virtual functions. Method overriding is called runtime polymorphism. It is also called late binding.
When overriding a method, you change the behavior of the method for the derived class. Overloading a method simply involves having another method with the same prototype.
Caution: Don't confused method overloading with method overriding, they are different, unrelated concepts. But they sound similar.
Method overloading has nothing to do with inheritance or virtual methods.
Following are examples of methods having different overloads:
namespace method_overloading
Note: In the code if you observe display method is called two times. Display method will work according to the number of parameters and type of parameters.
When and why to use method overloading
Use method overloading in situation where you want a class to be able to do something, but there is more than one possibility for what information is supplied to the method that carries out the task.
You should consider overloading a method when you for some reason need a couple of methods that take different parameters, but conceptually do the same thing.
Method overloading showing many forms.using System;
namespace method_overloading_polymorphism{Class Program{Public class Shape{Public void Area (float r){float a = (float)3.14 * r;// here we have used function overload with 1 parameter.Console.WriteLine ("Area of a circle: {0}",a);}Public void Area(float l, float b){float x = (float)l* b;// here we have used function overload with 2 parameters.Console.WriteLine ("Area of a rectangle: {0}",x);}public void Area(float a, float b, float c){float s = (float)(a*b*c)/2;// here we have used function overload with 3 parameters.Console.WriteLine ("Area of a circle: {0}", s);}}Static void Main (string[] args){Shape ob = new Shape ();ob.Area(2.0f);ob.Area(20.0f,30.0f);ob.Area(2.0f,3.0f,4.0f);Console.ReadLine ();}}}
Things to keep in mind while method overloading
If you use overload for method, there are couple of restrictions that the compiler imposes.
The rule is that overloads must be different in their signature, which means the name and the number and type of parameters.
There is no limit to how many overload of a method you can have. You simply declare them in a class, just as if they were different methods that happened to have the same name.
Method Overriding:
Whereas Overriding means changing the functionality of a method without changing the signature. We can override a function in base class by creating a similar function in derived class. This is done by using virtual/override keywords.
Base class method has to be marked with virtual keyword and we can override it in derived class using override keyword.
Derived class method will completely overrides base class method i.e. when we refer base class object created by casting derived class object a method in derived class will be called.
Example:
// Base class
Output
---------------------
Derived Class Method
Derived Class Method
Constructors and Destructors:
Classes have complicated internal structures, including data and functions, object initialization and cleanup for classes is much more complicated than it is for simple data structures. Constructors and destructors are special member functions of classes that are used to construct and destroy class objects. Construction may involve memory allocation and initialization for objects. Destruction may involve cleanup and deallocation of memory for objects.
- Constructors and destructors do not have return types nor can they return values.
- References and pointers cannot be used on constructors and destructors because their addresses cannot be taken.
- Constructors cannot be declared with the keyword virtual.
- Constructors and destructors cannot be declared const, or volatile.
- Unions cannot contain class objects that have constructors or destructors.
Constructors and destructors obey the same access rules as member functions. For example, if you declare a constructor with protected access, only derived classes and friends can use it to create class objects.
The compiler automatically calls constructors when defining class objects and calls destructors when class objects go out of scope. A constructor does not allocate memory for the class object it’s this pointer refers to, but may allocate storage for more objects than its class object refers to. If memory allocation is required for objects, constructors can explicitly call the new operator. During cleanup, a destructor may release objects allocated by the corresponding constructor. To release objects, use the delete operator.
Example of Constructor
class C
{
class D