2+ yrs .Net Interview Questions and Answers for Quick Reference

1. What is the difference between Web Services and WCF.

Ans. 

A. WCF Services = Web Services + Remoting + Security + Reliability + Messaging Queue

B. Not only that, hosting is also one of the powerful feature in WCF where the service can be hosted in Self Hosting, Hosting in Windows Services, Hosting on another Service etc.

C. Supports DataContractSerializer which is fast and can serialize fields and properties.

D. Integrated Logging mechanism.

2. What are the different ways of hosting a WCF service.
Ans.

A. Hosting on Console application

B. Hosting on Windows application

C. Hosting on Windows services

D. Hosting on IIS

E. Hosting on WAS(Windows Activation Service) 

3. Explain the different types of triggers in SQL Server.
Ans.

A. DDL Trigger- Trigger fires on DDL Commands

B. DML Trigger- Trigger fires on DML Commands

C. InsteadOf Trigger- Trigger fires on View updation

4. Difference between BasicHttpBinding and WSHttpBinding.
Ans.

A. BasicHttpBinding does not enable message level security while the WSHttpBinding enables Message level as well as Transport level security.

B. BasicHttpBinding has the default windows authentication while the WSHttpBinding support WS* authentication and security.

C. BasicHttpBinding only supports HTTP to access the service while WSHttpBinding suppors HTTP and HTTPS(secure)

D. Data which travels through the BasicHttpBinding is in XML format and no encryption allowed while the data travels through WSHttpBinding goes in Encrypted format.

5. What are the different types of assemblies available in .NET?
Ans.

A. Private Assembly

B. Shared Assembly

C. Satellite Assembly

6. What is a strong name and how do you give a strong name to an assembly?
Ans.

Unique identification of an assembly called as strong name. By strong name we can differentiate the assemblies which are having the same name.

We can generate the Strong name using the command:

SN -K dllName

7. What is InsteadOf trigger.
Ans. 

To update the Views, InsteadOf trigger is used. This is the only use of InsteadOf trigger. There is no use except this.

8. Can we use Insert/Update statements in views in SQL SERVER?

Ans. 

No, In general, View made to works only on the Query/Select command. So we can't have DML commands inside the View. So no Insert/update operations are allowed.
But there is a provision where we can make the views as updatable by using the DML statements inside the views but it is more complicated when there are views which are created by using the joins in the queries.
So its not preferable to make the view as updatable.

9. What are abstract classes and Interface and what the difference between the two.
Ans.

When the class does not provides the full functionality, the class must be declared as the abstract class.

There are 2 types of abstract classes-

A. Partial Abstract Class (Abstract Class)- Class which can support the abstract members(methods, properties) as well as concrete members(methods, properties), the class can be declared as the abstract class.

Abstract class works based on the child class memory. We can't create the object of the abstract class, only the reference can be created for the abstract class.

All the abstract members must be overrides in the child class using the Override keywords.

B. Fully Abstract class (Interface) - The collection of abstract members (methods, properties) is called as interface.

Interface contains all the abstract members.

When you have limited scope for the functionality, Abstract class is better but when there is the requirement to implement the global functions, interface is best way to do.

e.g. When u have some feature which can be implemented in several classes and classes are interrelated, use Abstract class but when the feature can be application level and used by various independent classes, use Interface.

10. What are the advantages of Interface over abstract classes?
Ans.

When you have some feature which can be implemented in several classes and classes are interrelated, use Abstract class but when the feature can be application level and used by various independent classes, use Interface.

Interfaces are more rigid than Abstract classes.

e.g. let's say, i have a method called Show() to show the message in various classes, we can have interface for this. Now let's say, I have implemented this interface in 100 classes where I want to use the Show() method to show some message.

Tomorrow there is some requirement to have the new Print Functionality to let's say in 50 various classes. Now the one way is to add this Print() in the same interface so that we can just implement it to those classes. But what about the rest 50, where we don't want this print.. So this is drawback of Interface.

That is the reason the Single Responsibility principle and then the interface Segregation Principle came where a class/interface should have only one responsibility. Like in the above example, there are more responsibility and got the problem.

Abstract class is best when the scope is limited. Let's say I want to calculate the Area of few shapes. So we can say that this is limited as few classes can use this so we can create the abstract class with the abstract method called Area and then implement to those classes by inheriting the abstract class.

The scope of the Abstract class is till the immediate child class. So you can't use it in grand child or grandparent classes.

11. What is a sealed class?
Ans.

When the class provides full functionality, we can declare the class as Sealed Class. Full functionality means, the class doesn't need anything from outside like loading the external files etc. The sealed class can’t be inherited and can't be extended. We can create the object of sealed class so instantiation of the sealed class is possible.when the class is self-dependent, the class be made as sealed class. 
Overall when we want the class prevented to be inherited, we can declare the class as sealed class. Also If we want that our method should not be overridable, we can create the methods as sealed method.
E.g.If you see the definitions of the datatypes, they all are sealed by default becasue they cant be extended.
public sealed class String : IComparable, ICloneable, IConvertible, IComparable<string>, IEnumerable<char>, IEnumerable, IEquatable<string>
{
  // Summary:
  //     Represents the empty string. This field is read-only.
  public static readonly string Empty;

  // Summary:
  //     Initializes a new instance of the System.String class to the value indicated
  //     by a specified pointer to an array of Unicode characters.
  //
  // Parameters:
  //   value:
  //     A pointer to a null-terminated array of Unicode characters.
  //
  // Exceptions:
  //   System.ArgumentOutOfRangeException:
  //     The current process does not have read access to all the addressed characters.
  //
  //   System.ArgumentNullException:
  //     value is null.
  //
  //   System.ArgumentException:
  //     value specifies an array that contains an invalid Unicode character, or value
  //     specifies an address less than 64000.
  [CLSCompliant(false)]
  [SecurityCritical]
  public String(char* value);
.... 
Here we can see that String class is of Sealed type.We can create the object of the sealed class as:
String obj = new String();
bu we cant inherit these classes as they are not inheritable.

12. What kind of authentication mechanism you have used in your WCF project.
Ans.

There are various authentication modes which can be used for the WCF service like-

A. No Authentication- When the service doesn't requires any authentication and its public to access and use, this type of authentication mode is used.

B. Windows Authentication – This type of service depends on the windows credential so if the user is having the windows credentials, they can use and access the service.

C. Form Authentication – This type of authentication requires certain and valid user name and password to access the service.

D. Certificate Based – There are the secure cervices where each request needs certain authentication mechanism which can be the 3rd party like .X509 certificates to validate the access requests.

E. Custom Authentication- This can be mixed with two or more authentication mechanism.

F. Token Based Authentication – Depends on the token provided by the service provider. So based on the token, the client can access the service.

13. How do you configure a WCF Service to use Network Authentication?

Ans. 

We need to set the remote settings for this.

Below is the reference url:

http://technet.microsoft.com/en-us/library/cc742824.aspx

14. What is Garbage Collection? How is Garbage Collector invoked in .NET?
Ans.

When the heap memory is filled with the objects and there is no memory left to accommodate the new object, Garbage collector gets called by the CLR. So it's an activity which is initiated by the run time (CLR). When the garbage collector gets called, it tries to find out each referenced objects which are in use by the applications. The objects which are not reachable, it marks them to delete. Based on the reachable objects, the garbage collector prepares the object graph, which has the reference of each reachable object. Now based on the object graph which contain the object generations too, the Garbage collector checks for the generation 0 objects and marks them for deletion and move rest of the objects to generation 1. The heap memory gets compacted for the new object and new object gets placed in the heap memory.

This is the uncertain and un-deterministic process as the Garbage collector doesn't know when it will be called. Its all based on the capacity memory of the heap. When the heap memory get filled and a new object is initiated, the runtime (CLR) calls the Garbage collector.

15. Can you force Garbage Collector to be invoked from c# code?
Ans.

Yes, When we have something called the unmanaged objects(C++, VC++,VB 6.0), then we need to explicitly release the memory. To do this, we can use the Dispose() method to free-up these object.

Sometimes, we need to force the garbage collector to be called to free-up the memory, so we can use the GC.Collect() method to do so.

16. How is var keyword used in .NET.Difference between var and dynamic keywords.
Ans. 

var keyword is newly introduces with the .net 3.5 and it is used to make the assignment for any type of data. It can store any type of data irrespective of its datatype.

So when we don't know that what type of data, the certain process will return, we can use the var keyword.

e.g.

var connection = new SqlConnection(connectionString);

Here the connection variable can store the SQLConnection type.

Dynamic keyword is newly introduces with the .net 4.0 version and is used to keep not only the any type of data but also the reference will be constant.

For the var, the type is made at the compile time while in case of Dynamic; the type is inferred in runtime.

e.g.

var customer = new Customer();

customer.GetCustomers();

Here the compiler will check for the GetCustomers()method. If the GetCustomers() method doesn't exists, it will show error during the compilation.

But for the dynamic,

dynamic  customer = new Customer();

customer.GetCustomers();

Here the compiler will not check for the GetCustomers() method during the compilation. But at the run-time, if the method is not available, it will throw error.

So the main use of dynamic is when we don't want the compiler should check for certain errors during compilation. It will skip the error if they are of dynamic type. 

17. Difference between Stored Procedures and Functions.
Ans.

Stored Procedure and Functions are the database objects which are the pre-compiled names SQL statements.

A. Stored procedure can take in as well as Out parameters while function can take only in parameters'.

B. Stored Procedure may or may not return the value while the Function must return a value. Returning a value in stored procedure depends on the input parameter. If the input parameter is of type out, then it will return the value.

C. We can use the function inside the stored procedure but stored procedure can't be used inside a function.

18. What are the different types of contracts available in WCF
Ans.

A. Service Contract- In Interface

B. Operation Contract - For Operations

C. Data Contract -Based on custom type

D. Message Contract - For Custom message

E. Fault Contract - For Error or Exception Handling

19. What is the static variable and what are the static variables in dot net.
Ans.

When the variable is shared by multiple class members (method, properties etc), we can make that variable as Static (in VB.Net Shared). To access these variables, we don't need to create the object of the class. We can directly call the static class members using the Class name. These variables get loaded when the class gets loaded in to the memory.

20. If I have 2 interfaces with same method same parameter and same return type. Both interface implemented from one Class. Then how can i call to these methods.
Ans.

Two interfaces with the same methods and same parameters can be implemented using the external interface functionality, rather than internal interface.
By default, when we implement the interface, we need to implement all the method to the implemented class.
But if the methods are same, then we can take the help of explicit interface as:
interface inf1
{
 void Print();
 void Show();
}
interface inf2
{
 void Print();
 void Show();
}

Now we will implement these interfaces in a single class:

class MyChildClass: inf1, inf2

{
 public void inf1.Print() // explicit interface call
 {
  //implement Print() method details for the first interface
 }
 public void inf1.Show()
 {
  //implement Show() method details for the first interface
 }
 public void inf2.Print()
 {
  //implement Print() method details for the second interface
 }
 public void inf2.Show()
 {
  //implement Show() method details for the second interface
 }
}

21. Can method overloading and overriding possible in simultaneously in program.
Ans.

Yes, both overloading and overriding concept can be implemented simultaneously between the parent can child classes as:

Class MyBaseClass

{
 public void Print()
 {
   // Print method implementation
 }
 public void Print(string fileName) // overloaded method
 {
   // Print method implementation with the file name
 }
 public virtual void Print()
 {
   // Print method implementation
 }
}
Class ChildClass:MyBaseClass
{
 public override void Print() // overriding implementation
 {
   // Print method implementation
 }
}

22. What is "using" keyword?
Ans.

"using" keyword is used in 2 scenarios:
1. To write the namespace as:
using System.Data.SqlClient;

2. To clean up the memory automatically after the use of object as:
using(var f = new SqlCommand())
{
 // some other iomplementation
}

The above code will delete the memory used by the 'f' object after the completion of the transaction.

23. What is dispose and finalize method and how it works
Ans.

Finalize and Dispose methods comes under the System.GC namespace and used to free up the memory occupied the objects. Garbage collector uses these objects to free up the memory.

When there is no enough memory to allocate the new object in the Heap, Garbage collector gets called automatically to free up the memory. It mainly creates the object graph and finds the objects which are not used since longer time. Based on the generations, it removes the objects.
Dispose method is called manually by programmer to remove the objects.
It uses IDisposable interface which has the Dispose method and this can be implemented in the code.