Types of classes in c#

Types of classes avalable in C#:

1.Instance class

2.Abstract class

3.Sealed class

4.Static class

5.partial class

6.nested class

 1.Instance class:

Instance class is a class on which we are allowed to create many instances or object.

*An instance class can act as a parent class as well as child class

*When we allow instance on a class ,there is a possability of increase in the memory consumption.

*Allowed depth of inheritance in the child class is 4. 

2.Abstract class:

 Abstract class is class which contain  0 or more abstract member( methods,properties ,indexer,event)  .

* Abstract is an incomlet class.

*We must give implimention to the abstract member in your derived class.

*If u are not giving implimention to the abstract member in your derived class then you should declare your derived class as method.

*We can not be able to create an object of an abstract class(since it incomplet).

*We can create a variable for the abstract class.

Note:

    you need to create as abstract class when you have family of related class which shaire some common bahaviour and having some uncommon bahaviour.

->Understanding abstract class  and interface become very important when we are writting the Framework.

Sample code:

3.Sealed class:

A sealed class is a class which can not act as a base class for any other class.

*sealed class can never be a parent class

*all the members declared in the sealed class become sealed member By default.

Q).when u declare ur class as sealed calss?

Ans:When u think that ur class is having fully funactionly and if u do'nt want to allow any ane to override

Q).Can we  declare a vartual or abstract method in a sealed class?

Ans: NO, bec virtual and abstract member bahaviour is allowed to be modified in the derived class.

Sample code:

public partial class sealed_class : System.Web.UI.Page
{
    protected void Page_Load(object sender, EventArgs e)
    {
        A a1 = new A();
        int r1 = a1.m1(10, 20);
        Response.Write(r1);
    }
}
public sealed class A
{
    public int m1(int x, int y)
    {
        return x + y;

    }
}

4.Static class:

Static class is a class in which we can only create static member But in case instance class ,we can create both instance nember as well as static member.

*A static class not act as Base class as Derived.

*static class can not participate in inheritance.

Note:

if u supposed declare the class as static class then no need to create object for accessing varibele but we can  access variable and method ussing class name 

Sample code: 

public partial class Static_class : System.Web.UI.Page
{
    protected void Page_Load(object sender, EventArgs e)
    {
        int r1 = A.x;
        int r2 = A.m(10, 20);
        Response.Write(r2);

    }
}
public static class A
{
    public static int x = 10;
    public static int m(int x, int y)
    {
        return x + y;
    }
}
Note: in this class without object we are accessing variable bec only for static class 

5.partial class:

  Partial class is useful when the class functionality is too big (i.e when number of lines of code in the class is too big) and when a developer want to share some of the functionalities with other developers this is useful.

6.Nested class:

 A class define as another class call as nested class.

-> A type define as another type call as nested type.
 ->A Struct define as another struct call as nested struct.
 ->32 level of nesting class is allowed in a class .

Sample code:

public partial class Nested_class : System.Web.UI.Page
{
    protected void Page_Load(object sender, EventArgs e)
    {
        D d = new D();
        int r2 = d.x;
        int r3=d.m1();
        Response.Write(r2);
        Response.Write(r3);
        D.E e1 = new D.E();
        int r4 = e1.y;
        int r5 = e1.m2();
        Response.Write(r4);
        Response.Write(r5);

      }
}
public class D
{
    public int x = 10;
    public int m1()
    {
        return 20;
    }
    public class E
    {
        public int y = 30;
        public int m2()
        {
            return 40;
        }
    }
}