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What is A class?

Ans: Class is a template of object

What is A object?

Ans: Object is a instance of class.

ex:

a class name book

public class book

{

}

object of the class book is 

book objbook=new book ();

Encapsulation: Encapsulation is way to hide data, properties and methods from outside the world or 

outside of the class scope and exposing only necessary thing.Encapsulation complements Abstraction. Abstraction display only important features of a class and Encapsulation hides unwanted data or private data from outside of a class.It hides the information within the object and prevents from accidental corruption.

Abstraction: Abstraction is one of the principle of object oriented programming. It is used to display only necessary and essential features of an object to ouside the world.Means displaying what is necessary and encapsulate the unnecessary things to outside the world.Hiding can be achieved by using "private" access modifiers.

The word abstract means a concept or an idea not associated with any specific instance.

The abstraction is done when we need to only inherit from a certain class, but not need to instantiate objects of that class. In such case the base
class can be regarded as "Incomplete". Such classes are known as an "Abstract Base Class".

Abstract Base Class

There are some important points about Abstract Base Class :

1. An Abstract Base class can not be instantiated; it means the object of that class can not be created.
2. Class having abstract keyword and having, abstract keyword with some of its methods (not all) is known as an Abstract Base Class.
3. Class having Abstract keyword and having abstract keyword with all of its methods is known as pure Abstract Base Class.
4. The method of abstract class that has no implementation is known as "operation". It can be defined as abstract void method ();
5. An abstract class holds the methods but the actual implementation of those methods is made in derived class.

What is Constructor and type of Constructor?

Ans: Constructors are the special member function with the same name as its class. Constructor is used to initialize the objects of that class type with some initial value. Advantages of constructor is that it is invoked (called) automatically as soon as the object of that class is created. This is also known as automatic initialization of objects.

Characteristics of constructor:

Constructor should be declared in public section.

No return type can be specified for constructors. Not even void type can be specified for return type in constructor. So constructor can't return values.

Constructors are invoked automatically when objects are created.

Constructor function can have default arguments.

Other member function can be called from constructor.

They can't be inherited.

Example:

Here, as soon as the object S1 is declared, its variables m, n is initialized to the value zero.

Parameterized constructor:-

A constructor can also take arguments. A constructor having some argument in it is called parameterized constructor. They allow us to initialize the various data element of different objects with different values.

We have to pass the initial values as arguments to the constructor function when an object is declared. This can be done in two ways:

· By calling the constructor explicitly

< Classname > = (value, value,...........);

· By calling the constructor implicitly

(value, value, ..............);

Copy constructor

As the name depicts, copy constructor copies value of one object to a different object inside a same class.

Syntax:

Sample (sample &);

The argument to a copy constructor will always pass by reference method if we pass argument by value method compiler will show error 'out of memory'. The reason is that when an argument is passed by value, a copy of it is constructed. Hence, copy constructor call itself again and again to copy the argument and computer will display message out of memory.

Example:

Integer (integer &k)

{

N=k.n;

}

And this constructor will be called as:

Integer int3 (int1);

This will copy the value of object int1 to int3.

Or this can be called by this: integer int3;

Int3=int1; // calling copy constructor

Default constructor

The constructor that accepts no parameter is called default constructor. If a class has no precise constructor defined then the compiler will provide a default constructor.

Dynamic constructor

We can also use constructor to allocate memory while creating objects. This will enable the system to allocate the right amount of memory for each object, thus resulting in the saving of memory. Allocation of memory to object at the time of their construction is known as dynamic construction of objects.

Example:

This will result in dynamic memory allocation.

What is a Partial class?

Ans: Instead of defining an entire class, you can split the definition into multiple classes by using partial class keyword. When the application compiled, c# compiler will group all the partial classes together and treat them as a single class. There are a couple of good reasons to use partial classes. Programmers can work on different parts of classes without needing to share same physical file

Ex:

Public partial class employee

{

Public void somefunction()

{

}
}

Public partial class employee

{

Public void function ()

{

}

}

Difference between Abstract and Interface

Abstract Class:

-Abstract class provides a set of rules to implement next class
-Rules will be provided through abstract methods
-Abstract method does not contain any definition
-While inheriting abstract class all abstract methods must be override
-If a class contains at least one abstract method then it must be declared as an “Abstract Class”
-Abstract classes cannot be instantiated (i.e. we cannot create objects), but a reference can be created
-Reference depends on child class object’s memory
-Abstract classes are also called as “Partial abstract classes”
-Partial abstract class may contain functions with body and functions without body
-If a class contains all functions without body then it is called as “Fully Abstract Class” (Interface)Interface:

-If a class contains all abstract methods then that class is known as “Interface”
-Interfaces support like multiple inheritance
-In interface all methods r public abstract by default
-Interfaces r implementable
-Interfaces can be instantiated, but a reference cannot be created

What are differences between Array list and Hash table?

Ans: 1) Hash table store data as name, value pair. While in array only value is store.

2) To access value from hash table, you need to pass name. While in array, to access value, you need to pass index number.

3) you can store different type of data in hash table, say int, string etc. while in array you can store only similar type of data.

What are differences between system.stringbuilder and system.string?

The main difference is system.string is immutable and system.stringbuilder is a mutable. Append keyword is used in string builder but not in system.string.

Immutable means once we created we cannot modified. Suppose if we want give new value to old value simply it will discarded the old value and it will create new instance in memory to hold the new value.

What are the differences between Application object and session object?

Ans: The session object is used to maintain the session of each user. If one user enter in to the application then they get session id if he leaves from the application then the session id is deleted. If they again enter in to the application they get different session id.
But for application object the id is maintained for whole application. 

s it possible to set the session out time manually? 

Ans: Yes we can set the session out time manually in web.config.

What is boxing and unboxing concepts in .net? 

Ans: Boxing is a process of converting value type into reference type

Unboxing is a process of converting reference type to value type.

What are the differences between value type and reference type?

Ans: Value type contain variable and reference type are not containing value directly in its memory.

Memory is allocated in managed heap in reference type and in value type memory allocated in stack. Reference type ex-class value type-struct, enumeration

Is it possible to host the website from desktop?

Ans: Yes 

Why we go for page rendering in Asp.Net Page life cycle?

Ans: Browser understands an only html control that’s why in page rendering we will convert the aspx controls into html controls.

What are difference between GET and POST Methods?

Ans:

GET Method (): 

1) Data is appended to the URL.
2) Data is not secret.
3) It is a single call system
4) Maximum data that can be sent is 256.
5) Data transmission is faster
6) this is the default method for many browsers

POST Method (): 

1) Data is not appended to the URL.
2) Data is Secret
3) it is a two call system.
4) There is no Limit on the amount of data. That is characters any amount of data can be sent.
5) Data transmission is comparatively slow.
6) No default and should be explicitly specified.

What is the difference Grid View and between Data Grid (Windows)?

Ans:

1) GridView Control Enables you to add sorting, paging and editing capabilities without writing any code.
2)GridView Control Automatically Supports paging by setting the ‘PagerSetting’ Property.The Page Setting Property supports four Modles 

a. Numeric(by default)
b. Next Previous
c. NumericFirstLast
d. Next PreviousLast

3)It is Used in asp.net
4)GridView Supports RowUpdating and RowUpdated Events.
5)GidView is Capable of Pre-Operations and Post-Operations.
6)GridView Has EditTemplates for this control
7)It has AutoFormat

DataGrid(Windows) 

1)DataGid Control raises single Event for operations
2)DataGird Supports the SortCommand Events that occur when a column is Soted.
3)DataGrid Supports UpdataCommand Event that occurs when the UpdateButton is clicked for an item in the grid.
4)DataGrid is used in Windows GUI Application.
5)It doesnot have EditTemplates for this control
6)It doesnot have AutoFormat

If I write System.exit (0); at the end of the try block, will the finally block still execute?

Ans: No in this case the finally block will not execute because when you say system.exit(0),the control immediately goes out of the program, and thus finally never executes.

What are the different levels of State management in ASP.NET?

Ans:

State management is the process by which you maintain state and page information over multiple requests for the same or different pages.

There are 2 types State Management:

1. Client – Side State Management
This stores information on the client's computer by embedding the information into a Web page, a uniform resource locator (url), or a cookie. The techniques available to store the state information at the client end are listed down below:

a. View State – Asp.Net uses View State to track the values in the Controls. You can add custom values to the view state. It is used by the Asp.net page framework to automatically save the values of the page and of each control just prior to rendering to the page. When the page is posted, one of the first tasks performed by page processing is to restore view state.

b. Control State – If you create a custom control that requires view state to work properly, you should use control state to ensure other developers don’t break your control by disabling view state.

c. Hidden fields – Like view state, hidden fields store data in an HTML form without displaying it in the user's browser. The data is available only when the form is processed.

d. Cookies – Cookies store a value in the user's browser that the browser sends with every page request to the same server. Cookies are the best way to store state data that must be available for multiple Web pages on a web site.

e. Query Strings - Query strings store values in the URL that are visible to the user. Use query strings when you want a user to be able to e-mail or instant message state data with a URL.

2. Server – Side State Management
a. Application State - Application State information is available to all pages, regardless of which user requests a page.

b. Session State – Session State information is available to all pages opened by a user during a single visit. 

What is difference between constants, read-only and, static?

Constants: The value can’t be changed

Read-only: The value will be initialized only once from the constructor of the class.

Static: Value can be initialized once.

What is the cross page post backing?

Asp.Net 2.0 fixed this with built-in features that allowed us to easily send information from one page to another.

Button control has property PostBackUrl that can be set to URL of any page in our ASP.Net WebSite where we want to transfer all form values to.
Along with that Asp.Net 2.0 Page class has a property PreviousPage that allows us to get reference to the Page object that initiated the postback (in other words to get the actual reference to the Page object of the aspx page on which user clicked the Submit button on a HTML form).

So for example lets create two sample pages in our Web Application:  

• SourcePage.aspx
• DestinationPage.aspx

In SoucePage in Html form we will put two TextBox controls (one for First Name and one for Last Name) and one Button component  and set its PostBackUrl property to "~/DestinationPage.aspx".

SourcePage.aspx:

    <form id="form1" runat="server">

        <div>

            First Name:&nbsp;<asp:TextBox ID="FirstName" runat="server"></asp:TextBox><br />

            Last Name:&nbsp;<asp:TextBox ID="LastName" runat="server"></asp:TextBox><br /><br />

            <asp:Button ID="Button1" runat="server" Text="Submit To Destination Page"PostBackUrl="~/CrossPagePostbacks/DestinationPage.aspx" />

        </div>

    </form>

When our user clicks the Submit button, all the values from the HTML Form on SourcePage.aspx will be transfered to the DestinationPage.aspx and we will also be able to get reference to the SourcePage.aspx in our DestinationPage with the PreviousPage property like this:

So in our DestinationPage.aspx.cs code-behind we can easily access two TextBox controls on SourcePage.aspx and show them in two label controls like this:

    protected void Page_Load(object sender, EventArgs e)

    {

        // first check if we had a cross page postback

        if ( (PreviousPage != null) && (PreviousPage.IsCrossPagePostBack) )

        {

            Page previousPage = PreviousPage;

            TextBox firstName = (TextBox)previousPage.FindControl("FirstName");

            TextBox lastName = (TextBox)previousPage.FindControl("LastName");

            // we can now use the values from TextBoxes and display them in two Label controls..

            labelFirstName.Text = firstName.Text;

            labelLastName.Text = lastName.Text;

         }

    }

You probably noticed that we first checked if PreviousPage property of current page (DestinationPage.aspx) is NOT NULL, this is done to avoid running our code in case that user opens our DestinationPage.aspx directly, without running a cross page postback.

Also here we checked the another PreviousPage property called IsCrossPagePostBack to see if we really had a CrossPagePostback.
(If Server.Transfer is used to redirect to this page, IsCrossPagePostBack property will be set to FALSE.

TIP: We can be completely sure that we have a  real CrossPagePostback ONLY IF:

1. Page.PreviousPage is NOT NULL,
2. PreviousPage.IsCrossPagePostback is true

This important to check to avoid errors in code.

Now this is very useful and i'm sure you are eager to use this in your next project. But wait, we are not over yet!

Finding the controls on PreviousPage with FindControl method and type-casting them from object to their real type is a little messy.
It feels like there must be a better solution for this!

And here it is: We can use the <%@ PreviousPageType %> directive in the header of our DestinationPage.aspx like this

    <%@ PreviousPageType VirtualPath="~/SourcePage.aspx" %>

to declare our previous page type, and then we can access Public properties of the PreviousPage without typecasting.
Now all we need to do is to create some public properties on our SourcePage.aspx.cs to expose data/Controls we want to the destionation page:

    public partial class SourcePage : System.Web.UI.Page

    {

        public string FormFirstName

        {

            get { return FirstName.Text; }

        }

        public string FormLastName

        {

            get { return LastName.Text; }

        }

    }

And then we can change the Page_Load code in our DestinationPage.aspx to much cleaner code like this:

    protected void Page_Load(object sender, EventArgs e)

    {

        // first check if we had a cross page postback

        if ( (PreviousPage != null) && (PreviousPage.IsCrossPagePostBack) )

        {

            SourcePage prevPage = PreviousPage;

            // we can now use the values from textboxes and display them in two Label controls..

            labelFirstName.Text = prevPage.FormFirstName;

            labelLastName.Text = prevPage.FormLastName;     

        }

    }

SourcePage type used in the code is offcourse name of the partial class defined is SourcePage.aspx.cs that inherits System.Web.UI.Page that is automatically created for us when we created new WebForm in VisualStudio.

This code is much cleaner and easier to follow, there is no ugly typecasting, just simple property values to use to retrieve the data from previous page.

When should you use Abstract Class vs Interface while programming?

 Ans: When we want that sub class must implement all the methods of base class. In such a situation we will implement the interface. In the other hand when we want only some method of base class in our sub class then use base class as abstract class.

What is the difference between application exception and system exception?

Ans: The difference between application exception and system exception is that system exceptions are thrown by CLR and application exceptions are thrown by applications.

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