.NET Framework Interview Questions and answers

.NET Framework Interview Questions

1. What are the collection classes?

The .NET Framework provides specialized classes for data storage and retrieval.

list the object-oriented concepts

Inheritance
Abstraction
Polymorphism
Encapsulation

2. What is difference between interface inhertance and class inheritance?

If its a interface inheritance and the inheritad class is not a abstact class or a interface class then all the methods in the supper class needs to be implemented.
Class inheritance no need such thing.

3. What are Abstract base classes?

Abstact Class is nothing but a true virtual class..
This class cannot be instantiated instead it has to be inherited.
The method in abstract class are virtual and hence they can be overriden in the child class.

4. When is web.config called?

Web.config is an xml configuration file. It is never directly called unless we need to retrieve a configurations setting.

5. What does connection string consist of?

Server, user id, password, database name.

6. What is a runtime host?

The runtime host is the environment in which the CLR is started and managed.

7. What inheritance does VB.NET support?

Single inheritance using classes or multiple inheritance using interfaces.

8. Differences between application and session ?

The application level variable hold value at the application level and their instances are destroyed when the no more client access that application, whereas session correspond to a individual user accessing the application.

9. What is web application virtual directory?

Virtual directory is the physical location of the application on the machine.
By default it’s - inetpub/wwwroot

10. If cookies is disabled in client browser, will session tracking work?

No, maintaining value in cookie wont be possible. In that case you have to make use of other ways to maintain state of the data on page.
you can check whether client support cookies or not by using
Request.Browser.Cookies property.

11. What is a Process, Session and Cookie?

Process - Instance of the application
Session - Instance of the user accessing the application
Cookie - Used for storing small amount of data on client machine.

12. Explain serialization?

Serialization is a process of converting an object into a stream of bytes.
.Net has 2 serializers namely XMLSerializer and SOAP/BINARY Serializer.
Serialization is maily used in the concept of .Net Remoting.

13. What is the difference between overloading and overriding ? how can this be .NET?

Overriding - Method has the same signature as the parent class method.
Overloading - Method having diff parameters list or type or the return type may be different.

14. Explain friend and protected friend?

Friend/Internal - Method, Properties in that class can be accessed by all the classes within that particular assembly.
Protected Friend/Protected Internal - Methods, Properties can be accessed by the child classes of that particular class in that particular assembly.

15. What is isPostback property?

This property is used to check whether the page is being loaded and accessed for the first time or whether the page is loaded in response to the client postback.
Example:
Consider two combo boxes
In one lets have a list of countries
In the other, the states.
Upon selection of the first, the subsequent one should be populated in accordance. So this requires postback property in combo boxes to be true.

16. Can you give an example of when it would be appropriate to use a web service as opposed to a non-serviced .NET component?

When to use Web Service:
1. Communicating through a Firewall When building a distributed application with 100s/1000s of users spread over multiple locations, there is always the problem of communicating between client and server because of firewalls and proxy servers. Exposing your middle tier components as Web Services and invoking the directly from a Windows UI is a very valid option.

2. Application Integration When integrating applications written in various languages and running on disparate systems. Or even applications running on the same platform that have been written by separate vendors.

3. Business-to-Business Integration This is an enabler for B2B intergtation which allows one to expose vital business processes to authorized supplier and customers. An example would be exposing electronic ordering and invoicing, allowing customers to send you purchase orders and suppliers to send you invoices electronically.

4. Software Reuse This takes place at multiple levels. Code Reuse at the Source code level or binary componet-based resuse. The limiting factor here is that you can reuse the code but not the data behind it. Webservice overcome this limitation. A scenario could be when you are building an app that aggregates the functionality of serveral other Applicatons. Each of these functions could be performed by individual apps, but there is value in perhaps combining the the multiple apps to present a unifiend view in a Portal or Intranet.

When not to use Web Services:
1. Single machine Applicatons When the apps are running on the same machine and need to communicate with each other use a native API. You also have the options of using component technologies such as COM or .NET Componets as there is very little overhead.

2. Homogeneous Applications on a LAN If you have Win32 or Winforms apps that want to communicate to their server counterpart. It is much more efficient to use DCOM in the case of Win32 apps and .NET Remoting in the case of .NET Apps

17. How to retrieve the last error occured in the application?

Use Server.GetLastError();

18. How to clear the last error occured in the application?

Use Server.ClearError();

19. Whats MSIL, and why should my developers need an appreciation of it if at all?

          

MSIL is the Microsoft Intermediate Language. All .NET compatible languages will get converted to MSIL. MSIL also allows the .NET Framework to JIT compile the assembly on the installed computer.

20. Can I use the Win32 API from a .NET Framework program?

Yes. Using platform invoke, .NET Framework programs can access native code libraries by means of static DLL entry points.
Here is an example of C# calling the Win32 MessageBox function:
using System;
using System.Runtime.InteropServices;

class MainApp
{
[DllImport("user32.dll", EntryPoint="MessageBox")]
public static extern int MessageBox(int hWnd, String strMessage, String strCaption, uint uiType);

public static void Main()
{
MessageBox( 0, "Hello, this is PInvoke in operation!", ".NET", 0 );
}
}