Basic C# OOP Concept - CodeProject

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syed shanu, 23 Jan 2015 CPOL

Basic C# OOP Concept

This Article will explain avery simple way to understand the basic C# OOP Concept

Download ShanuBasicCSharpOOPConceptV1.4.zip 1.4 MB

Tableof Contents

1. Class

2. Object

3. Variable

4. Method

5. Access Modifiers

6. Encapsulation

7. Abstraction

8. Inheritance

9. Polymorphism

10. AbstractClass/Method

11. Virtual Method

12. Sealed Class/Method

13. Static Class/Method

14. Interface

Introduction

There are many explanations that we can find in internet about C# OOP, but here in my article I will give a very simple example.

In this article, I will use a House like the houses we live in as a realtime example for easy understanding of OOP Concept in

C#.

1. Class

Classis a like a Blueprint.

What is a blueprint?

Blueprint is outline drawing of our actual plan. For example if we plan to build our new home ,The Engineer will explain our new

house plan with a blue print as shown in the image below. Once we finalized the plan the engineer will start building the house

with same plan.

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Same like blueprint class is an outline of program. Using the class we can write our own method and declare the variables and

using the objects we can access the class Method and Variables. The class will be complete with Variables, Methods and Objects.

For more easy understanding of OOP with real world example here I have explained a class with House. We can imagine a House

as an example for a Class. In a house, we will have rooms like living room, bedroom, kitchen and items like TV, fridge etc. House

owner can access and use all the rooms and rooms' items. Same like this in a Class will have a group of Methodsand Variables.

Rooms and Rooms' Items are example for Methods and Variables. So now, we have a complete house with all rooms and rooms'

items. House owner can access and use all the rooms and Rooms' Items. To access and use a Class, methods and variables here

we use Objects. Objects are instance of a class. We will see details about objects in the next section.

What will happen if there are no rooms and items in a House? It will be empty and no one can use the house until it has all the

rooms and Items. See the below image as an example for the empty house.


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Now this empty house is a Class .So what is the use of a Class without Methods and variable.

Now lets see an example for a Complete House with Rooms and items.


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So here, we have a complete house. Similarly, the Class will be complete with group of Variables, Methods and Objects. We can

see details of all this in next sections of this article.

Class and objects are the base concept of OOP Object Oriented Programming.

Here is an Example of Class > Class should be started with the Keyword class and next we give the name for our class we can

give any meaning full name as Class Name, next we will have the Open and close brackets.

class ShanuHouseClass1 {

}

2. Object

As we have already seen that, House Owner will access and use all the Rooms of the House and its Items. Similarly, to access all

Class Method and Variable we use Objects. We can create one or many object for a same Class. Example we can say for a house

there might be one or many owners.

Here is an example of Object >Here objHouseOwner is the Object for a class which will be used to access all variable and

Method of a class.

ShanuHouseClass1 objHouseOwner = new ShanuHouseClass1();

3.Variable

Variables are used to store our value. Our value can be numeric or characters for example to store a Phone no we can use int type

variable and to store our name we can use string type variable with name for each variable.

Variables can be local or Global. For Example, we can say if we buy a new TV , TV Service man will come and setup the TV in our

home .He will give his contact number for future contacts .Usually what we do is take a memo paper and write his contact

number and keep it in a common place or in a wallet of ours. If we keep the memo in a Commonplace everyone who is visiting

our house can see that contact number. Global or public variables are similar to this. If we declared the variable as Global, All the

Methods inside the class can access the variable. If we store the memo Only in our wallet, we can see the contact number. Localor private variables are similar to this.

Syntax for variable:

AccessModifiers DataType VariableName

By default the AccessModifiers are by private, we can also use public to variable.

Example of Variable:

int noOfTV = 0; publicString yourTVName;

privateBoolean doYouHaveTV = true;

// Example Program

class ShanuHouseClass {

int noOfTV = 2; publicString yourTVName = "SAMSUNG";

staticvoid Main(string[] args)

{ ShanuHouseClass objHouseOwner = new ShanuHouseClass();

Console.WriteLine("You Have total " + objHouseOwner.noOfTV + " no of TV :"); Console.WriteLine("Your TV Name is :" + objHouseOwner.yourTVName);


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}

}

In Above example program I have declared two variables inside a class. In main method I have created object for class. Here we

can see using the object we can access the variable of a class and display the output.

Main Method is the default Method of C#, where every console and windows application will start the program execution, In the

Main Method, we can declare the Object for the class and use the object, and we can access all variables and Methods of a Class.

For example, we can say there will be entrance gate for every house. Using the entrance gate we can enter inside our house.

Similarly, to run our program there should be some default program execution starting Method. Main method will be useful inthis program execution starting point. Whenever we run our C# Console or windows application, first the Main method will be

executed .From the main method we can create an object for our other classes and call their Methods.

4. Method or Functions:

Method is a group of code statement .Now here we can see the above example program with method.

class ShanuHouseClass

{ int noOfTV = 2;

publicString yourTVName = "SAMSUNG";

publicvoid myFirstMethod() {

Console.WriteLine("You Have total " + noOfTV + "no of TV :"); Console.WriteLine("Your TV Name is :" + yourTVName);

Console.ReadLine(); }


{ ShanuHouseClass objHouseOwner = new ShanuHouseClass();

objHouseOwner.myFirstMethod();}

Note: Most of developers were wondering about what is the difference between the Method and Function, both Methods and

Functions are the same. Here in my article, I will use Method instead of functions. However, there is one difference in Methods

and Functions, In OOP Languages like C#, Java etc. We use the term Method while the nonOOP programming like C etc. we

use the term Function.

What is the use of Methods?

Another realtime example lets take our mobile phone, we can say as we have Mobile phone and store many Songs in it.

However, we always like to listen to the selected songs. It will be boring and hard for us to select our favorite song every time

and play it. Instead of doing the same work repeatedly, we use the playlist. In playlist, we can add allfavorite songs of ours. Just

click on the playlist of our collections and listen to the music. This will make our work easier and we dont need to do the same

thing again and again. Methods are used like a playlist where we can write all our repeated code in one Method and just call the

method wherever we needed.

Here we can see more details about the Method.

In a house, there might be one big room or multiple rooms but each room will have different facilities, similarly in a class we can

write one or multiple Methods. In a house, there might be two or three Bedrooms. Here the room name is Bedroom, but each

bedroom can be different by size, color etc. This means same Rooms with different type. Similarly, in a class we can create more

than one method with the same name but different parameter. In OOP its called as Polymorphism we can see details about

Polymorphism later on in this article.

Syntax for the Functions

AccessModifiers ReturnType MethodName ParameterList

AccessModifiers: We will see more details about this Topic later on.


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ReturnType: If our Method returns any value then we use the return Type with any Data Type as String, int etc., if our Method

does not return any value then we use the type Void.

MethodName: Here we give our Name for every Method, which we create

ParameterList: ParameterList or Arguments, which we pass to the function.

Here is an example of Method >

Method with Void Type: Void is a keyword which will not return any data from the Method, for example we can see the below

Method with void Type, here in this method we display all our output using the Console.WriteLine and have used theConsole.ReadLine ; to get the Input. This Method has all Input and Output Operation but this method dont return any value.

// Function with void and no parameter here void means no return type publicvoid veranda()

{ Console.WriteLine("Welcome to Veranda");

Console.WriteLine("How Many Chairs Do you have in your Veranda"); NoofChair = Convert.ToInt32(Cons ole.ReadLine());

Console.WriteLine("I have total " + NoofChair + " Chairs in my Veranda"); }

Method with Return Type: Method with return type will return some result, which can be used in our program, for example,

here we have Method TVNAMEwith return Type as String. We can say in our home we might have a TV in our LivingROOM and

in the parents bedroom and also in kids bedroom .We might have different TV brand in each room, suppose if we want to know

each room TV Brand Name then we need to enter the same code 3 times. Instead of writing the same code again, we can use a

method with Return Type.

// Function with Return type as String publicstring TVNAME() {

Console.WriteLine("Enter Your TV Brand NAME"); YOURTVName = Console.ReadLine();

return YOURTVName; }

Method with ParameterList:So far, we have seen methods without arguments. Arguments are used to pass some data to the

Method to do our process in a better way. For example, we can say we want to do a painting, to our bedrooms. We need to get

the opinions of all the member of the house in order to know there choices of color for each bedroom, we can pass the member

Name and their favorite color as parameter to a Method.

//Function with parameter publicvoid BedRoom(String nameandColor)

{ Console.WriteLine(nameandColor);

}

Same Method name with different arguments are called as Method over loading, here we can see below .Both Method has the

same name but it has different arguments.

// Same Function Name with Different Paramenter

publicvoid BedRoom(String MemberName,String Color) {

Console.WriteLine(Mem berName + " Like " + Color + "Color"); }

The Complete Class with Main Method Example:

class ShanuHouseClass1

{ int NoofChair = 0;

publicString YOURTVName; privateBoolean DoyouHaveTV = true;


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// Function with void and no parameter here void means no return type publicvoid veranda()

{ Console.WriteLine("Welcome to Veranda");

Console.WriteLine("How Many Chairs Do you have in your Veranda"); NoofChair = Convert.ToInt32(Cons ole.ReadLine());

Console.WriteLine("I have total " + NoofChair + " Chairs in my Veranda"); }

// Function with Return type as String publicstring TVNAME()

{ Console.WriteLine("Enter Your TV Brand NAME");

YOURTVName = Console.ReadLine(); return YOURTVName;

}



}

// Same Function Name with Different Paramenter publicvoid BedRoom(String MemberName,String Color)

{ Console.WriteLine(Mem berName + " Like " + Color + "Color");

}


{ ShanuHouseClass1 objHouseOwner = new ShanuHouseClass1();

objHouseOwner.veranda(); String returnvalue = objHouseOwner.TVNAME();

Console.WriteLine("Your TV BRAND NAME IS: "+returnvalue); objHouseOwner.BedRoom("My Name is Shanu I like Lavender color");

objHouseOwner.BedRoom("My Name is Afraz I like Light Blue color"); objHouseOwner.BedRoom("SHANU", "Lavender");

Console.ReadLine();

}

}

The Output of above class is here:

5. Access Modifiers:

Access Modifiers are nothing but the Usage and Limitation of our type like variable, Methods and Class. For Example we can say

it as a security limit.


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private

public

internal

protected

protected internal

This six are the basic Access modifiers which we used in our C# Class/method and in Variables.

Private:

Lets take our House Example .We will have a Security Guard in House, His duty is till the Entrance of the house. He cannot go inside the

house and access all the things. In this case we can create a SecurityGuardClass and declare the variable and method for Security as private

.

Public:

House Owners are public to the class where they can access all classes related to the House. They have no restrictions to access their

house.

Protected: Only the main class and derived class can have access of protected variable or method. For example servants and Guests are

example for the Protected. For Example Servants can go to all room and do cleaning and other activates. However, they have limitations ofaccess in the house, as they cannot take rest in a bed of house owner.

Internal:Access limit of variable or method is within a project. For example lets consider in our project we have more than one class and

we have declared a variable as internal in one class. Lets see an example program for internal variable.

publicclass sampleInternalClass {

internalString myInternal = "Iam Internal Variable"; }



publicvoid myFirstMethod() { Console.WriteLine("You Have total " + noOfTV + "no of TV :");

Console.WriteLine("Your TV Name is :" + yourTVName);

}

staticvoid Main(string[] args) {

ShanuHouseClass objHouseOwner = new ShanuHouseClass(); objHouseOwner.myFirstMethod();

sampleInternalClass intObj = new sampleInternalClass();

Console.WriteLine("Internal Variable Example :" + intObj.myInternal); Console.ReadLine();

} }

Protected Internal: Protected Internal variable or Method has limitation with in a project of class or Derived class. Here is a sample

program for Protect Internal Variable .In this example I have used the Inheritance .we will see in detail about Inheritance more detail in this

article.

publicclass sampleProtectedInternalClass {

protectedinternalString myprotectedInternal = "Iam Protected Internal Variable";

publicvoid protectedInternalMethod() {

Console.WriteLine("Protected Internal Variable Example :" + myprotectedInternal);


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}

} publicclass derivedClass : sampleProtectedInternalClass

{ publicvoid derivedprotectedInternal()

{ Console.WriteLine("Derived Protected Internal Variable Example :" + myprotectedInternal);

} }



publicvoid myFirstMethod()

{ Console.WriteLine("You Have total " + noOfTV + "no of TV :");

Console.WriteLine("Your TV Name is :" + yourTVName);

}


ShanuHouseClass objHouseOwner = new ShanuHouseClass(); objHouseOwner.myFirstMethod();

sampleProtectedIntern alClass intObj = new sampleProtectedInternalClass();

intObj.protectedInternalMethod();

derivedClass proIntObj = new derivedClass(); proIntObj.derivedprotectedInternal();

Console.ReadLine();

} }

Note: The main and major things we need to know in OOP concept areEncapsulation, Abstraction,Polymorphism and

Inheritance.We will discuss them in detail in this article.

6. Encapsulation:

Encapsulation is to hide the member or variable to outside class. In our house example, I have already told that House security guard

limitation is till the entrance of the house. The security guard doesnt need to know about what is happening inside the house. Therefore,

the House Owner will hide all the happenings to Security guard for more safety. The hiding and limitation are called as Encapsulation.

For example, we have two Classes the first one is Houseclass and the other class as houseSecurityClass

Here we can see all the variables are wrap into a class where houseSecurityClass is set as public, so the Houseclass can access that, but

houseClass has both Public and private variable where the private variable of a class cannot be accessed outside of the class.

publicclass houseSecurityClass

{ publicint noofSecurity;

publicString SecurityName = String.Empty;

}

publicclass Houseclass

{ privateint noofLockerinHosue = 2;

publicstring OwnerName = String.Empty; }

7. Abstraction :

Abstraction is to show and share some common information to the user. Lets take our House example, in our house we

will have servant, servants can go to all rooms and do cleaning and other works. The house owner can give full rights or some partial rights


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to the servant for accessing his house. Here we can see an example program as private declared variables and Methods are not shared with

servant but the public variable and Methods are shared with servant.

publicclass HouseServerntClass {

privateint SaftyLoackerKeyNo = 10001;

publicString roomCleanInstructions = "Clean All rooms";

privatevoid saftyNos() {

Console.WriteLine("My SaftyLoackerKeyNo is" + SaftyLoackerKeyNo); }

publicvoid roomCleanInstruction()

{ Console.WriteLine(roomCleanInstructions);

}

}

8. Inheritance:

Inheritance is used to reuse the code. In Protected Internal Access modifier section we have already seen an example program forInheritance. Inheritance is nothing but accessing and using all base class variable and methods in the Derived Class. Inheritance can be

Single level Inheritance: With one Base class and one derived Class for example.

publicclass baseClass

{ privatevoid privateMethod()

{ Console.WriteLine("private Method");

}

publicvoid publicMethod() {

Console.WriteLine("This Method Shared");

} } publicclass DerivedClass : baseClass

{ staticvoid Main(string[] args)

{ DerivedClass obj = new DerivedClass();

obj.publicMethod(); //obj.privateMethod() ; //This will be error as private method can not be accessed in Derived Class

}

}

Note: Some time users might be not clear of what Base class is and what Derived class is. Base class is the super class and derived class is

the classes which inherit the base class.

Here we can see a simple Inheritance where the base class is the GuestVist and derived class is the HouseOwnerClass. Here

HouseOwnerClass class inherits the base class of GuestVist

HouseOwnerClass.Here HouseOwnerClass class inherits the baseclass of GuestVist

class GuestVist {

publicvoid Guestwelcomemessage() {

Console.WriteLine("Welcome to our Home"); }

publicvoid GuestName() {

Console.WriteLine("Guest name is: Shanu"); }


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} class HouseOwnerClass : GuestVist


{ HouseOwnerClass obj = new HouseOwnerClass();

obj.Guestwelcomemessage(); obj.GuestName();


}

Multi level Inheritance: With more than one Derived Class for example. Here we can see an example first base class is derived in

DerivedClass1 and then the DerivedClass1 is derived in DerivedClass2 .Now from DerivedClass2 we can access both baseClass

and DerivedClass1 variable and methods.

publicclass baseClass

{ privatevoid privateMethod()

{ Console.WriteLine("private Method");

}

publicvoid publicMethod() {

Console.WriteLine("This Method Shared"); }

} publicclass DerivedClass1 : baseClass

{ publicvoid DerivedClass1()

{ Console.WriteLine("Derived Class 1");

} }

publicclass DerivedClass2 : DerivedClass1 {


DerivedClass2 obj = new DerivedClass2(); obj.publicMethod(); obj.DerivedClass1();

//obj.privateMethod() ; //This will be error as private method can not be accessed in Derived Class }

}

Multiple Inheritance:

Will the .Net Support Multiple Inheritance?

The Answer to this Question is No. In C #, its not possible to write a Multiple Inheritance using Class.

What is Multiple Inheritance? Multiple Inheritance is nothing but we can have more than one class and we can inherit both

Classes in our derived class.

What will happen if I write a Multiple Class Inheritance Using C#?

Lets take our example House .Here we have the derived Class as HouseOwnerClass and have Two More classes as GuestVist

and FriendsandRelationsClass.

Now suppose for our house both Guest and Friend have visited. For this, we write above three classes and inherit the two classes

in our derived class.

When I write the Multiple Inheritance in C #, it will display the warning message during our code and execute our program. The

Warning message will be as Expected and interface

See the below image which shows the Warning error message while I write Multiple Inheritance.


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Then how can we use the Multiple Inheritance

Interface will be used for Multiple Inheritance.

9. Polymorphism :

Ploy means more than one form. In the beginning of the Article at Method Section, we have already seen an example of

Polymorphism. Same method name with different parameter is an example for the polymorphism.

Method Overloading andMethod Overriding will be used in polymorphism. Polymorphism have two types of execution one is

Compile Time Polymorphism and the other one is called the Run time Polymorphism.

Method Overloading:

Method overloading are nothing but same Method name will be used for more than one method with different Argument .

Here is an example program for the Method Overloading .As we can see here Method name BedRoom has been used for two

Method but the parameter for both methods are different.

class HouseOwnerClass {



}

// Same Function Name with Different Paramenter


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publicvoid BedRoom(String MemberName, String Color)

{ Console.WriteLine(Mem berName + " Like " + Color + "Color");

}


HouseOwnerClass objHouseOwner = new HouseOwnerClass();

objHouseOwner.BedRoom( "My Name is Shanu I like Lavender color"); objHouseOwner.BedRoom("My Name is Afraz I like Light Blue color");

objHouseOwner.BedRoom("SHANU", "Lavender"); Console.ReadLine();

}

}

Method Overriding:

The difference between the Method Overloading and Overriding are.In Method Overloading we will have same method name

with different argument.

In Method Overriding we will have same Method Name same Argument and same type but method overriding can only be used

in the derived class, Method Overriding cannot be done in the same class.

We will see how Method Overriding can be used in AbstractMethod, Virtual Methodand in Sealed Methodkindly refer to that

section in this article.

10. Abstract Class/Method:

Abstract Class: Abstract class will have a keyword abstract.

abstractclass GuestVist

{ }

The Abstract class will be as a super class for all our class. Abstract class cannot be accessed by an object, which means wecannot create an object for an abstract class..

What will happen when we create an object for an Abstract Class?

Here we can see an error warning message as An instance of an abstract class cannot be created when I try to create an object

for my abstract class.

Abstract class can have both Abstract Method and normal Method. In Abstract Class at least one Abstract Method should be

declared. In addition, derived class should override the abstract method. To access the abstract method we should use the

override keyword in our derived class.


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What will happen if we create an abstract method but which is not override in derived class?

Here we can see an abstract class has an abstract method, But the abstract method is not override in the derived class. See the

below image for the warning message displaying as class must implement the abstract member.

Here we can see an example of Abstract Class and for Abstract Method in detail.

In this example, we can see an abstract class, which has normal Method and Abstract Method. Abstract Methods; do not have

body part in Abstract Class, which means we can only declare an Abstract Method at Abstract Class, There should be minimum

one Abstract Method in an Abstract Class.


{ publicvoid Guestwelcomemessage()

{ Console.WriteLine("Welcome to our AbstractHome");

} publicvoid GuestName()

{ Console.WriteLine("Guest name is: Abstract");

} publicabstractvoid purposeofVisit();

}

// derived class to inherit the abstract classpublicclass Houseclass : GuestVist


{ Houseclass objHouse = new Houseclass();

objHouse.Guestwelcomemessage(); }

publicoverridevoid purposeofVisit()

{ Console.WriteLine("Abstract just came for a Meetup and spend some time ");

} }

11. Virtual Class/Method:

Virtual method is very useful in our daytoday programming.

What is virtual Method and what is the use of Virtual Method?

Take our House example one guest confirms, as today total five persons will visit your home. For this, we write a function as

message display as five Guest visiting our home. Once Guest visits, we see their total 20 persons have visited. In Some cases it

might be increase or decrease we will come to know when they reach us.

In that case, the guest will be as a Separate Class and House will be as separate class. Without changing the message in Guest

class how can we change the data in our Derived class?

What is the Difference between Abstract Method and Virtual Method?


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Both similarities use the override keyword. Abstract Method can only be declared in Abstract Class, which means no body part

for abstract method in Abstract class. However, for virtual it can have body part.

See the example program below. Here we have both Abstract Method and Virtual Method. In Abstract class, the virtual method

says as total five guests but in the derived Class program, the message was override as 20 guests. See the final output in below.

Guess what will be displayed for Virtual Method? Will the result be 5 Guests or 20 Guests check for the output below the

program.


{

publicabstractvoid purposeofVisit(); // Abstract Method

publicvirtualvoid NoofGuestwillvisit() // Virtual Method

{ Console.WriteLine("Total 5 Guest will Visit your Home");

} }

class AbstractHouseClass : GuestVist {

publicoverridevoid purposeofVisit() // Abstract method Override {

Console.WriteLine("Abstract just for a Meetup and spend some time "); }

publicoverridevoid NoofGuestwillvisit()// Virtual method override

{ Console.WriteLine("Total 20 Guest Visited our Home");

}


AbstractHouseClass objHouse = new AbstractHouseClass();

objHouse.purposeofVisit(); objHouse.NoofGuestwillvisit();


}

The Complete Program :

abstractclass GuestVist {

publicvoid Guestwelcomemessage() {

Console.WriteLine("Welcome to our AbstractHome"); }

publicvoid GuestName() {

Console.WriteLine("Guest name is: Abstract"); }

publicabstractvoid purposeofVisit(); // Abstract Methodpublicvirtualvoid NoofGuestwillvisit() // Virtual Method

{

Console.WriteLine("Total 5 Guest will Visit your Home");

} } class AbstractHouseClass : GuestVist {

publicoverridevoid purposeofVisit() // Abstract method Override {

Console.WriteLine("Abstract just for a Meetup and spend some time "); }

publicoverridevoid NoofGuestwillvisit()// Virtual method override { Console.WriteLine("Total 20 Guest Visited our Home");

}


AbstractHouseClass objHouse = new AbstractHouseClass();


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objHouse.Guestwelcomemessage();

objHouse.purposeofVisit(); objHouse.NoofGuestwillvisit();


}

output:

12. Sealed Class/Method:

Sealed Class: As name says this class cannot be inherited by other classes.

Take our House Example. In a house, the Houseowner can have a secret room, as might be official or financial rooms. The owner

dont want others to access his official room. The sealed class will be useful in those cases.

Sealed class can be declared using the keyword Sealed. If one class is declared as Sealed, it cannot be inherited in other derived

classes.

What will happen when we inherit sealed class in our derived class?

Lets see an example when I try to inherit my sealed class from my derived class. It shows me the below warning message.

Here we can see an example program of Sealed Class.

publicsealedclass OwnerofficialRoom {

publicvoid AllMyPersonalItems()

{ Console.WriteLine("All Items in this rooms are personal to me no one else can access or inherit me" ); } }

class HouseSealedClass{


OwnerofficialRoom obj = new OwnerofficialRoom(); obj.AllMyPersonalItems();


}

Sealed Method: If we declared a method as sealed that specific method cannot be override in the derived class.


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Lets see our house class here I have base class with Virtual Method and virtual Sealed method.

The Virtual method can be override in the derived class .But the Virtual Sealed Method cannot be override in sealed class.

//Base Class with Sealed Method publicclass OwnerOfficialroomwithrestriction {

publicvirtualvoid message() {

Console.WriteLine("Every one belongs to this house can access my items in my room except my sealed Item" );

}

publicvirtualsealedvoid myAccountsLoocker() {

Console.WriteLine("This Loocker can not be inherited by other classes" ); }

} //Deraived method which inherits Selaed Method class class HouseSealedClass : OwnerOfficialroomwithrestriction {

publicoverridevoid message() {

Console.WriteLine("overrided in the derived class"); }

publicoverridevoid myAccountsLoocker()

{

Console.WriteLine("The sealed method Overrides"); }}

13. Static Class/Method :

We have already learned about what is Sealed Class in this Article; now lets see what are Static Class and Static Method.

Both Static and Sealed Class cannot be inherited.

What is the Difference between Static Class and Sealed Class?

We can create an Object instance for the Sealed Class, we can see in my sealed class section I have created a sample Sealed

class and in Main Method I have created an object to access the sealed Class. And in a Sealed Class both Static and nonStatic

methods can be written.

But for a Static Class its not possible to create an Object. In Static Class only Static members are allowed which means in a static

Class its not possible to write nonstatic method.

We can say our main method as an example for the Static method. When we create a console application in c# we can see each

class will have a default main method. In my article I have explained that when an Console or Windows application start execute

first the main method will be executed .There is no need to create an object for the main method since it was been declared as a

static method.


{}

Another interesting one in Static class is that memory will be allocated for all static variable and methods during execution but

for the non static variable and methods memory will be allocated only when the object for the class are created.

Lets take our same sealed class Example for our static Class and method.

What will happen when we inherit Static class in our derived class?

Lets see an example when I try to inherit my static class from my derived class. It shows me the below warning message.


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What will happen when we declare nonStatic method in a Static class?

Lets see an example when I try to create a nonStatic method at my Static Class.

What will happen when we create an object for the Static class?

Lets see an example when I try to create an object for my Static Class.

When we run the program we get the error message as Can not create an instance of a static class .Sorry Im using the Korean

Version of Visual Studio so the error message in Korean language.


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How to call the Static Class Method and variable without creating the Object?

Its simple just we can use the ClassName.Variable or Method Name for example OwnerofficialRoom.AllMyPersonalItems ;

See the below example with Static class

publicstaticclass OwnerofficialRoom {

publicstaticvoid AllMyPersonalItems() {

Console.WriteLine("All Items in this rooms are personal to me no one else can access or inherit me" );

}

}

class HouseStaticClass


{ OwnerofficialRoom.AllMyPersonalItems();

Console.ReadLine();

} }

The Output for the above program is here.

Is that possible to create a Static Method in nonStatic Class?

The answer is yes. We can create a Static Method to the non Static class. No need to create an object to access the static methodin nonstatic class. We can directly use the class name to access the Static method.

See the below example with Static method in nonstatic Class.

public class OwnerofficialRoom

{ publicstaticvoid AllMyPersonalItems()

{ Console.WriteLine("No need to create object for me just use my class name to access me :)");

}

publicvoid non_staticMethod() {

Console.WriteLine("You need to create an Object to Access Me :(");


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}

}

class StaticmethodClass {


// for statci method no need to create object just call directly using the classname. OwnerofficialRoom.AllMyPersonalItems();

// for nonstatic method need to create object to access the method.

OwnerofficialRoom obj = new OwnerofficialRoom(); obj.non_staticMethod();

Console.ReadLine();

} }

The Output for the above program is here.

14. Interface :

Interface is same like abstract class but in Interface we will have only method declaration but in abstract class we can have both method

declaration and method definition .Methods of Interface must be implemented in a implementing class

See the below Example program for an Interface. All the methods of Interface have been implemented in the class. As I have already told

you that c# dont support multiple inheritance for using multiple inheritance we can use Interface. This below program is an example for

multiple inheritance using Interface.


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interface GuestInterface {

void GuestWelcomeMessage(); void NoofGuestes();

} interface FriendsandRelationsInterface

{ void friendwelcomemessage();

void FriendName(); }

class HouseOwnerClass : GuestInterface, FriendsandRelationsInterface

{ publicvoid GuestWelcomeMessage()

{ Console.WriteLine("All guests are well come to our home");

}

publicvoid NoofGuestes() {

Console.WriteLine("Total 15 Guestes has visited"); }

publicvoid friendwelcomemessage()

{ Console.WriteLine("Welcome to our Home");

} publicvoid FriendName()

{

Console.WriteLine("Friend name is: Afraz"); } staticvoid Main(string[] args)


obj.GuestWelcomeMessage(); obj.NoofGuestes();

obj.friendwelcomemessage(); obj.FriendName(); Console.ReadLine();

} }

The Output will be like this.

In some cases we need to have certain methods which will be used in many derived classes. Each derived can implement

different functionality for those Methods. In These cases, we can use the Interface.

We can say our Guest and house example. For Guest the Welcome Message and No of Guest Function are common, but it

will be different for different owners in the same house, Guest might a fathers guest, Mothers Guest, Childrens Guest or Family


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Guest. Each guest can have different welcome message subject, but the functions are same as Message .lets consider now Father

is a Class, Mother is a class and Children are one Class. Both guestWelcome Message and Noofguest method are same for all. In

this case, we can create an Interface and declare both methods in the Interface. All father, mother and Children Classes can

inherit the interface and write their own method details.

Interface is similar to Abstract class but the major difference between the Abstract Class and the Interface are .In Abstract Class

there can be both Abstract Method and Non Abstract methods .But in Interface all methods are abstract by default which means

there is no non Abstract type method in the Interface. All the Methods declared in Interface should be override in the derived

class.

What will happen when nonabstract methods with body part are declared in an Interface?

It will display the warning message as unexpected modifier in Access modifier part and Unexpected Method body error

warning at message Body. See the below image for the details.

Example program for Interface:

interface GuestInterface {

void GuestWelcomeMessage(); void NoofGuestes();

} class HouseOwnerClass: GuestInterface

{ public void GuestWelcomeMessage()

{ Console.WriteLine("All guests are well come to our home");

}

public void NoofGuestes() {

Console.WriteLine("Total 15 Guestes has visited"); }



obj.GuestWelcomeMessage();

obj.NoofGuestes(); Console.ReadLine();

}

}

HistoryInitial release on 2014/11/05.

Article Updated on 2014/11/07




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syed shanuTeam Leader

India

His Blog

Syed Shanu is basically from Madurai, Tamil Nadu, India.He was been working in South Korea for past 8 years. He started

programming with Basic Language and C language from his high school at 1999.In 2005 he completed his Master of Computer

Application. He started his working Career from Dec 2004 with ASP.

He has 9+ years of Experience in Microsoft Technologies.

His work experience with Language and Technology starts from ASP and SQL Server, Then VB.NET and C# for PDA Application,

Touch Screen Application Development, Desktop Application, ASP.NET Web Application Development, MVC and WPF.

He loves to work with Microsoft technology as he started to work on .Net Frame Work version from 1.0 to 4.5.

He had worked with HMI Human Machine Interface programs like PLC, Nutrunner Tools, and Sensor programs, RFID programs,

Barcode programs and etc.

He also worked with Dotnetnuke .

He had worked with Projects like, Restaurant management with PDA AND Desktop Development, Hospital management withPDA, Desktop and Web development, Online Shopping Cart for web, Inventory Management for web, Asset Management for

desktop, SPC for Desktop, Factory Automation for Desktop, MES for both Web and Desktop, ERP for Both Web and Desktop.

He usually uses his free time to spend with his Family and go outing. He loves photography and Hiking.

Hes a Positive thinker, he always believes in Software field there is no problems with solution.

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