C# interview questions Set 2

1. What’s the implicit name of the parameter that gets passed into the set method/property of a class?

value. The data type of the value parameter is defined by whatever data type the property is declared as.
2. What does the keyword “virtual” declare for a method or property?
The method or property can be overridden.
3. How is method overriding different from method overloading?
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 name within the class.
4. Can you declare an override method to be static if the original method is non-static?
No. The signature of the virtual method must remain the same, only the keyword virtual is changed to keyword override.
1. To do: Re-word the answer for better clarity.
5. Can you override private virtual methods?
No. Private methods are not accessible outside the class.
1. Original answer: No, moreover, you cannot access private methods in inherited classes, have to be protected in the base class to allow any sort of access.
2. To do: Can a private method even be declared a virtual?
6. What are the different ways a method can be overloaded?
Different parameter data types, different number of parameters, different order of parameters.
7. If a base class has a number of overloaded constructors, and an inherited class has a number of overloaded constructors; can you enforce a call from an inherited constructor to a specific base constructor?
Yes, just place a colon, and then keyword base (parameter list to invoke the appropriate constructor) in the overloaded constructor definition inside the inherited class.
1. To do: question is to complex. It can be stated better.
8. Why is it a bad idea to throw your own exceptions?
Well, if at that point you know that an error has occurred, then why not write the proper code to handle that error instead of passing a new Exception object to the catch block?
Throwing your own exceptions signifies some design flaws in the project.
9. What’s a delegate?
A delegate object encapsulates a reference to a method.
10. What’s a multicast delegate?
It’s a delegate that points to and eventually fires off several methods.
20. How do you inherit from a class in C#?
Place a colon and then the name of the base class.
21. Can you prevent your class from being inherited by another class?
Yes. The keyword “sealed” will prevent the class from being inherited.
22. Can you allow a class to be inherited, but prevent the method from being over-ridden?
Yes. Just leave the class public and make the method sealed.
23. What’s an abstract class?
A class that cannot be instantiated. An abstract class is a class that must be inherited and have the methods overridden. An abstract class is essentially a blueprint for a class without any implementation.
24. When do you absolutely have to declare a class as abstract?
1. When at least one of the methods in the class is abstract.
2. When the class itself is inherited from an abstract class, but not all base abstract methods have been overridden.
25. What’s an interface class?
It’s an abstract class with public abstract methods all of which must be implemented in the inherited classes.
26. Why can’t you specify the accessibility modifier for methods inside the interface?
They all must be public. Therefore, to prevent you from getting the false impression that you have any freedom of choice, you are not allowed to specify any accessibility, it’s public by default.
1. To do: Clean up this answer.
27. Can you inherit multiple interfaces?
Yes, why not.
1. To do: Need a better answer.
28. And if they have conflicting method names?
It’s up to you to implement the method inside your own class, so implementation is left entirely up to you. This might cause a problem on a higher-level scale if similarly named methods from different interfaces expect different data, but as far as compiler cares you’re okay.
29. What’s the difference between an interface and abstract class?
In an interface class, all methods must be abstract. In an abstract class some methods can be concrete. In an interface class, no accessibility modifiers are allowed, which is ok in an abstract class.
30. What is the difference between a Struct and a Class?
Structs are value-type variables and are thus saved on the stack -> additional overhead but faster retrieval. Another difference is that structs CANNOT inherit. (questions courtesy of Eyal)

C# interview questions Set 1

Note: Please naviagate to the other set of questions by clicking the links in the "Other Questions" section on the right hand side

1. Does C# support multiple-inheritance?

No, use interfaces instead.

2. When you inherit a protected class-level variable, who is it available to?

Classes in the same namespace.

3. Are private class-level variables inherited?

Yes, but they are not accessible. Although they are not visible or accessible via the class interface, they are inherited.

4. Describe the accessibility modifier “protected internal”.

It is available to derived classes and classes within the same Assembly (and
naturally from the base class it’s declared in).

5. C# provides a default class constructor for me. I decide to write a constructor that takes a string as a parameter, but want to keep the constructor that has no parameter. How many constructors should I write?

Two. Once you write at least one constructor, C# cancels the freebie constructor, and now you have to write one yourself, even if there’s no implementation in it.

6.What’s the top .NET class that everything is derived from?

System.Object.

7. How to implement encapsulation in C#.

Through Properties.

8. What’s the difference between System.String and System.StringBuilder classes?

System.String is immutable. System.StringBuilder was designed with the purpose of having a mutable string where a variety of operations can be performed.

9.What’s the advantage of using System.Text.StringBuilder over System.String?

StringBuilder is more efficient in cases where there is a large amount of string manipulation. Strings are immutable, so each time it’s being operated on, a new instance is created.

10. Can you store multiple data types in System.Array?

No.

12. How can you sort the elements of the array in descending order?

By calling Sort() and then Reverse() methods.

13. What’s the .NET class that allows the retrieval of a data element using a unique key?

HashTable.

14. What class is underneath the SortedList class?

A sorted HashTable.

15. Will the finally block get executed if an exception has not occurred?

Yes.

16. What’s the C# equivalent of C++ catch (…), which was a catch-all statement for any possible exception?

A catch block that catches the exception of type System.Exception. You can also omit the parameter data type in this case and just write catch {}.

17. Can multiple catch blocks be executed?

No. Once the proper catch code fires off, the control is transferred to the finally block (if there are any), and then whatever follows the finally block.

18. Explain the three services model commonly know as a three-tier application.

Presentation (UI), business (logic and underlying code) and data (from storage or other sources).

19. What is the role of the DataReader class in ADO.NET connections?

It returns a read-only dataset from the data source when the command is executed.

Other ASP.Net related interview questions are available at
Set 1 of ASP.Net Interview questions or Asp.Net FAQs
Set 2 of ASP.Net Interview questions or Asp.Net FAQs
Set 3 of ASP.Net Interview questions or ASP.Net FAQs
New features of C# 4.0 is available at C# 4.0 FAQs or C# 4.0
Basic .Net questions are available at .Net Frame works FAQ or .Net interview question
Web Service interview question are available at Web Service Interview questions

Web Service Interview questions

Note: Please naviagate to the other set of questions by clicking the links in the "Other Questions" section on the right hand side

What are web services?
Web Services are business logic components which provide functionality via the Internet using standard protocols such as HTTP. Web Services uses Simple Object Access Protocol (SOAP) in order to expose the business functionality.SOAP defines a standardized format in XML which can be exchanged between two entities over standard protocols such as HTTP. SOAP is platform independent so the consumer of a Web Service is therefore completely shielded from any implementation details about the platform exposing the Web Service. For the consumer it is simply a black box of send and receive XML over HTTP. So any web service hosted on windows can also be consumed by any platform.
cCick on the link to know more about what are web services

What are the communication protocol of Web services?
Web services communcate through SOAP and HTTP protocols. Click on the link to know more about what is soap

What is the format of a SOAP message?
Generally SOAP message has two major sections, Header and Body.

What is UDDI ?
Full form of UDDI is Universal Description, Discovery and Integration. It is a directory that can be used to publish and discover public Web Services. For example tomorrow you wish to pusblish your web site and want to know

What is DISCO ?
DISCO is the abbreviated form of Discovery. It is basically used to club or group common services together on a server and provides links to the schema documents of the services it describes may require

What is WSDL?
Web Service Description Language (WSDL)is a W3C specification which defines XML grammar for describing Web Services.XML grammar describes details such as:- √ Where we can find the Web Service (its URI)? √ What are the methods and properties that service supports? √ Data type support. √ Supported protocols In short its a bible of what the webservice can do.Clients can consume this WSDL and build proxy objects that clients use to communicate with the Web Services. Full WSDL specification is available

What is file extension of Webservices ?
.ASMX is extension for Webservices.

How do you authenticate your web service?
you can use SOAP header to authenticate your web service. You may define a class and added as a SOAP header to the web method. While calling from client this has to be added to the SOAP header and should be passed along with the request.
To here to know more about Authenticating a web service with soap header

Can you overload a web method?
Web methods can be overloaded with the message property of the web method.

What is Web Service Enhancements ?
Web Services Enhancements for Microsoft .NET (WSE) is a .NET class library for building Web services using the latest Web services protocols, including WS-Security, WS-SecureConversation, WS-Trust, and WS-Addressing. WSE allows you to add these capabilities at design time using code or at deployment time through the use of a policy file.

What are the design points to be considered while designing a web service.
The return type of the web service should not be language specific. for exampe if you are building it .Net the return type should not be dataset, rather should be a string or an int which can be understood by all Languages.

Other ASP.Net related interview questions are available at
Set 1 of ASP.Net Interview questions or Asp.Net FAQs
Set 2 of ASP.Net Interview questions or Asp.Net FAQs
Set 3 of ASP.Net Interview questions or ASP.Net FAQs

New features of C# 4.0 is available at C# 4.0 FAQs or C# 4.0
Basic .Net questions are available at .Net Frame works FAQ or .Net interview question