.NET Interview Questions

1. What is a static class?

A static class is a class which can not be instantiated using the ‘new’ keyword. They also only contain static members, are sealed and have a private constructor.

2. What is static member?

A static member is a method, field, property or event that can be called without creating an instance of its defining class. Static members are particularly useful for representing calculations and data that are independent of object state.

3. What is static function?

A static function is another term for a static method. It allows you to execute the function without creating an instance of its defining class. They are similar to global functions. An example of a static function could be: ConvertFromFarenheitToCelsius with a signature as follows:

public static double ConvertFromFarenheitToCelsius (string valToConvert){//add code here}

4. What is static constructor?

A static constructor has a similar function as a normal constructor i.e. it is automatically called the first time a class is loaded. The differences between a conventional constructor are that it cannot be overloaded, cannot have any parameters nor have any access modifiers and must be preceded by thekeyword static. In addition, a class with a static constructor may only have static members.

5. How can we inherit a static variable?

6. How can we inherit a static member?

When inheriting static members there is no need to instantiate the defining class using the ‘new’ keyword.
public class MyBaseClass{MyBaseClass(){}public static void PrintName(){}
}
public class MyDerivedClass : MyBaseClass{MyDerivedClass (){}
public void DoSomething(){MyBaseClass.GetName();}
}

7. Can we use a static function with a non-static variable?

No.

8. How can we access static variable?

By employing the use of a static member field as follows:public class CashSales{//declare static member fieldprivate static int maxUnitsAllowed = 50;
//declare method to return maximum number of units allowed
public static int GetMaxUnitsAllowed (){Return maxUnitsAllowed;}
}The static field can now be accessed by simply doing CashSales.GetMaxUnitsAllowed(). No need to create an instance of the class.

9. Why main function is static?

Because it is automatically loaded by the CLR and initialised by the runtime when the class is first loaded. If it wasn’t static an instance of the class would first need to be created and initialised.

10. How will you load dynamic assembly?How will create assemblies at run time?

Load assembly:By using classes from the System.Reflection namespace.Assembly x = Assembly.LoadFrom( “LoadMe.dll” );
Create assembly;Use classes from System.CodeDom.Compiler;

11. What is Reflection?

The System.Reflection namespace provides us with a series of classes that allow us to interrogate the codebase at run-time and perform functions such as dynamically load assemblies, return property info e.t.c.

12. If I have more than one version of one assembly, then how will I use old version (how/where to specify version number?) in my application?

The version number is stored in the following format: …. The assembly manifest can then contain a reference to which version number we want to use.

13. How do you create threading in.NET? What is the namespace for that?

System.Threading;
//create new thread using the thread class’s constructor
Thread myThread = new Thread(new ThreadStart (someFunction));

14. What do you mean by Serialize and MarshalByRef?

Serialization is the act of saving the state of an object so that it can be recreated (i.e deserialized) at a later date.The MarshalByRef class is part of the System.Runtime.Remoting namespace and enables us to access and use objects that reside in different application domains. It is the base class for objects that need to communicate across application domains. MarshalByRef objects are accessed directly within their own application domain by using a proxy to communicate. With MarshalByValue the a copy of the entire object is passed across the application domain

15. What is the difference between Array and LinkedList?

An array is a collection of the same type. The size of the array is fixed in its declaration.A linked list is similar to an array but it doesn’t have a limited size.

16. What is Asynchronous call and how it can be implemented using delegates?

A synchronous call will wait for a method to complete before program flow is resumed. With an asynchronous call the program flow continues whilst the method executes.
//create objectSomeFunction objFunc = new SomeFunction();
//create delegateSomeDelegate objDel = new SomeDelegate(objFunc.FunctionA);
//invoke the method asynchronously (use interface IAsyncResult)IAsyncResult asynchCall = SomeDelegate.Invoke();

17. How to create events for a control? What is custom events? How to create it?

An event is a mechanism used in a class that can be used to provide a notification when something interesting happens. (typical evens in a windows application include: change text in textbox, double click or click a button, select an item in dropdown box).
A custom event is an event created by the user that other developers can use. For example assuming that we have a CashTransaction class and we have a bank balance property in that class. We may want to set-up an event that provides a notification when the bank balance drops below a certain amount. In order to produce an event the process would be roughly as follows:
Create the class for the event derived from EventArgs.Create a delegate with a return type of void.Create a class containing the method that will activate the event.Create a class with methods to handle the event.

18. If you want to write your own dot net language, what steps you will you take care?

We will need to ensure that the high level code is compiled to MSIL (Microsoft intermediate language) so that it can be interpreted by the CLR.

19. Describe the difference between inline and code behind - which is best in a loosely coupled solution?

The term ‘code behind’ refers to application code that is not embedded within the ASPX page and is separated out into a separate file which is then referenced from the ASPX page. Inline code is the traditional ASP architectural model where business logic code was embedded within the ASP page. Separating the business logic code from the presentation layer offers several advantages:
1) It allows graphic designers and web developers to work on the presentation layer whilst the application developers concentrate on the business logic.

2) The codebehind file is compiled as a single dll increasing the efficiency of the application

3) The codebehind model offers a true OO development platform

4) It speeds up development time as it allows developers to fully maximise the features of the .NET framework such as Cahing, ViewState, Session, Smart Navigation etc.

5) Code is much easier to maintain and susceptible for change.

6) The compiler and VS.NET provides much better support for error checking, intellisense and debugging when using the code behind model.

20. How dot net compiled code will become platform independent?

The reason for .NET was to cater for multiples languages on a single windows platform whereas the aim of Java was to be a single language on multiple platforms. The only way that .NET can be platform independent is if there is a version of the .NET framework installed on the target machine.

21. Without modifying source code if we compile again, will it be generated MSIL again?

No.

22. How does you handle this COM components developed in other programming languages in.NET?

Use TlbImp.exe to import the COM types into your .NET project. If no type library for the COM component then use System.Runtime.InteropServices

22. How does you handle this COM components developed in other programming languages in.NET?

Use TlbImp.exe to import the COM types into your .NET project. If no type library for the COM component then use System.Runtime.InteropServicesuse RegAsm.exe to call a .NET developed component in a COM application.

23. How CCW (Com Callable Wrapper) and RCW (Runtime Callable Wrappers) works?

CCW: When a COM application calls a NET object the CLR creates the CCW as a proxy since the COM application is unable to directly access the .NET object.RCW: When a .NET application calls a COM object the CLR creates the RCW as a proxy since the .NET application is unable to directly access the .COM object.

24. What are the new thee features of COM+ services, which are not there in COM (MTS)?

Role based security.Neutral apartment threading.New environment called context which defines the execution environment

25. What are the differences between COM architecture and.NET architecture?

.Net architecture has superseded the old COM architecture providing a flexible rapid application development environment which can be used to create windows, web and console applications and web services. .NET provides a powerful development environment that can be used to create objects in any .NET compliant language. .NET addresses the previous problems of dll hell with COM by providing strongly named assemblies and side-by-side execution where two assemblies with the same name can run on the same box.

26. Can we copy a COM dll to GAC folder?

No. It only stores .NET assemblies.

28. Can you explain what inheritance is and an example of when you might use it?

Inheritance is a fundamental feature of any OO language. It allows us to inherit the members and attributes from a base class to a new derived class. This leads to increased code reusability and also makes applications easier to develop, maintain and extend as the new derived class can contain new features not available in the base class whilst at the same time preserving the attributes inherited from the base class.

29. How can you write a class to restrict that only one object of this class can be created (Singleton class)?

Use the singleton design pattern.public sealed class Singleton{static readonly Singleton Instance=new Singleton();
static Singleton(){}
Singleton(){}
public static Singleton Instance{get{return Instance;}}}

30. What are virtual destructors?

A constructor can not be virtual but a destructor may. Use virtual destructors when you want to implement polymorphic tearing down of an object.

31. What is close method? How it different from Finalize and Dispose?

Finalise is the process that allows the garbage collector to clean up any unmanaged resources before it is destroyed.The finalise method can not be called directly; it is automatically called by the CLR. In order to allow more control over the release of unmanaged resources the .NET framework provides a dispose method which unlike finalise can be called directly by code.Close method is same as dispose. It was added as a convenience.

32. What is Boxing and UnBoxing?

Boxing is the process of converting a value type to a reference type. More specifically it involves encapsulating a copy of the object and moving it from stack to heap. Unboxing is the reverse process.

33. What is check/uncheck?

checked: used to enable overflow checking for arithmetic and conversion functions.unchecked: used to disable overflow checking for arithmetic and conversion functions.