DOT NET Interview Questions with Answers

When not to use Design Patterns?

Do not use design patterns in any of the following situations.

• When the software being designed would not change with time.

• When the requirements of the source code of the application are unique.

If any of the above applies in the current software design, there is no need to apply design patterns in the current design and increase unnecessary complexity in the design.

When to use Design Patterns?

Design Patterns are particularly useful in one of the following scenarios.

• When the software application would change in due course of time.

• When the application contains source code that involves object creation and event notification.

Benefits of Design Patterns:

The following are some of the major advantages of using Design Patterns in software development.

• Flexibility

• Adaptability to change

• Reusability

What are Design Patterns?

A Design Pattern essentially consists of a problem in a software design and a solution to the same. In Design Patterns each pattern is described with its name, the motivation behind the pattern and its applicability.

According to MSDN, "A design pattern is a description of a set of interacting classes that provide a framework for a solution to a generalized problem in a specific context or environment. In other words, a pattern suggests a solution to a particular problem or issue in object-oriented software development.

What is Com Marshler and its importance in .NET ?

Com Marshler is one of useful component of CLR. Its Task is to marshal data between Managed and Unmanaged environment .It helps in representation of data accross diffrenet execution enviroment.It performs the conversion of data format between manage and unmanaged code.By the helps of Com Marshlar CLR allows manage code to interoperate with unmanaged code.

Can you define what is SharePoint and some overview about this ?

SharePoint helps workers for  creating  powerful personalized interfaces only by dragging and drop pre-defined Web Part Components. And these Web Parts components also helps non programmers to get information which care  and customize the appearance of Web pages. To under stand it we take an example  one Web Part might display a user's information another might create a graph showing current employee status  and a third might show a list of Employees Salary. This is also possible that each functions has a link to a video or audio presentation.So now  Developers are unable to  create these Web Part components and make them available to SharePoint users.

What you thing about the WebPortal ?

Web portal is nothing but a page that allows a user to customize his/her homepage. We can use Widgets to create that portal we have only to drag and drop widgets on the page. The user can set his Widgets on any where on the page where he has to get them. Widgets are nothing but a page area that helps particular function to response. Widgets example are address books, contact lists, RSS feeds, clocks, calendars, play lists, stock tickers, weather reports, traffic reports, dictionaries, games and another such beautiful things that we can not imagine. We can also say Web Parts in Share Point Portal. These are one of Ajax-Powered.

Define SMTPclient class in DotNet framework class libarary?

Each classes in dotnet framework inclue some properties,method and events.These properties ,methods and events are member of a class.SMTPclient class mainly concern with sending mail.This class contain the folling member.
Properties:-
Host:-The name or IP address of email server.

Port:-Port that is use when sending mail.

Methods:-
Send:-Enables us to send email synchronously.

SendAsynchronous:-Enables us to send an email asynchronously.

Event:-
SendCompleted:-This event raised when an asynchronous send opertion completes.

What do you mean by three-tier architecture?

The three-tier architecture was comes into existence to improve management of code and contents and to improve the performance of the web based applications.There are mainly three layers in three-tier architecture.the are define as follows
(1)Presentation
(2)Business Logic

(3)Database

(1)First layer Presentation contains mainly the interface code, and this is shown to user. This code could contain any technology that can be used on the client side like HTML, JavaScript or VBScript etc.
(2)Second layer is Business Logic which contains all the code of the server-side .This layer have code to interact with database database and to query, manipulate, pass data to user interface and handle any input from the UI as well.

(3)Third layer Data represents the data store like MS Access, SQL Server, an XML file, an Excel file or even a text file containing data also some addtional databases are also added to those layers.

What is the Website Administrative Tool in ASP.NET 2.0?

In ASP.NET 2.0, while using Visual Studio 2005 Express Edition or above, the development IDE provides an interface for editing the web.config rather than manually editing the web.config.

In the IDE, click on "Website" and then on "ASP.NET Configuration". This shall open the Website configuration tool. Note that the Web Site Administration Tool is a set of prebuilt ASP.NET 2.0 webpages and resources that are located within the C:\Inetpub\wwwroot\aspnet_webadmin\2_0_40607 directory.

Before in my VB app I would just load the icons from DLL. How can I load the icons provided by .NET dynamically?

By using System.Drawing.SystemIcons class' for example

System.Drawing.SystemIcons.Warning produces an Icon with a warning sign in it. 

What are three test cases you should go through in unit testing?

1.Positive test cases (correct data, correct output).

2. Negative test cases (broken or missing data, proper handling).

3. Exception test cases (exceptions are thrown and caught properly).

Using COM components in .NET and How to add a reference to a COM component?

The .NET does not encourage the use of COM component directly inside the managed application! Although, the .NET framework contains utilities that enable COM components to be used inside the .Net applications seamlessly. How it is done? The .NET utilities like TlbImp generates the wrapper .NET assembly for the COM component which provides the same calling interface to the client as exposed by the COM component. Inside the wrapper methods, it calls the actual methods of the COM component and returns the result back to the caller. The generated wrapper .NET assembly is called the ‘Runtime Callable Wrapper’ or RCW.
To use a COM component in your Visual Studio.NET project, you need to add a reference of the COM component in the Reference node of the project node of the solution inside the solution explorer window. The great thing about Visual Studio.Net is that it allows you to add a reference to the COM component in exactly the similar way as you add the reference to the .NET assembly. The Visual Studio.NET automatically creates the runtime callable wrapper assembly for the referenced COM component.
To add a reference to a COM component, right click the ‘Reference’ node under the project node inside the solution explorer and select the ‘Add Reference…’ option. It will show you a user interface screen where you browse for the target COM component. When you have selected the component, press the ‘Select’ button and then press OK. This will add a new reference node in the Reference sub tree of the project. By selecting the added reference node, you can edit its properties from the properties window.
Note: The process of importing a COM component into .NET is called ‘COM interoperability with .NET’

What are XML Doc comments (comments start with three slashes ///)?

The XML Doc comments are special kind of comments that can be recognized by Document utility to automatically generate the documentation of your methods, types and regions.

How true it is that .NET and Java programs are quite in-efficient when compared to C++?

The startup of managed .NET and Java programs is definitely slower than the traditional C++ programs as it involves the hosting of CLR into managed application process in .NET and starting the JVM in a new process in case of Java. The execution also is a bit slower during the initial period of program execution as the intermediate code is translated to the machine code on the fly at runtime. But as the program runs various parts repeatedly, the execution gets pace too. Since, the CLR and JVM optimizes the code more efficiently than the static C++ compilers, the execution speed of the program may actually be faster after sometime of the program startup when most of the code is translated. Hence, in the longer run, the .Net and Java based programs should not be in-efficient when compared to C++. We used ‘should’ here as the actual performance depends on the particular implementation and implementation strategy.

What are the shortcomings of MS.NET platform?

The foremost short coming of .NET platform is that it is still the propriety of Microsoft. It is more coupled with the Microsoft Windows operating system and is implemented only on Microsoft Windows successfully. MS.NET desktop applications can run only on Microsoft Windows, Web based applications and web services can only be deployed on Microsoft Internet Information Server (IIS). Since, dot net framework contains a lot of utilities, components, and framework class libraries, the size of downloadable framework is quite large (25MB compared to 5MB size of JVM). Not all types of applications can be written in .NET managed applications, for example, you can’t write CLR or Operating System in your managed applications. The managed .Net applications are somewhat slower to start and run than the traditional Win32 applications. The compiled code of .Net managed applications is easier to de-compile back to the source code.

Why should one use MS.NET for software development?

Well, most of the software development all over the world is done on and for Microsoft Windows Operating System. Dot Net is now the standard software development environment for the Microsoft Windows operating system. It dramatically simplifies the development of windows, web based, data access applications, components, controls and web services. Dot net comes with amazing features like XML configuration, reflection, and attributes to ease the overall software development life cycle. Finally, the dot net is supported by the Microsoft Visual Studio Integrated Development Environment; the best IDE available for any software development environment. Visual Studio .NET (VS.NET) supports all the areas of software development from project creation to debugging and installation.

What does one need to build or execute .NET applications?

To execute a standalone .NET application (Windows or Console application), one needs to first compile all its constituent assemblies and modules including the executable assembly. Once, the constituent assemblies are compiled, one needs to make sure that the target system contains the .NET framework. The application can now be executed by running its executable assembly (the .exe file). The executable assembly (.exe) is a Win32 executable that hosts the .Net CLR (Common Language Runtime), which exists as a COM component, in its process space and initializes it. Once the CLR is hosted and initialized, the starting point of the .NET executable assembly is passed to the hosted CLR which starts the execution of the program by translating and executing the parts of the program code.

What is the difference between an executable assembly and a class library?

An executable assembly exists as the .exe file while a class library exists as the .dll file. Executable assembly represent executable applications having some entry (e.g., Main() method in C#). A class library, on the other hand, contains components and libraries to be used inside various applications. A Class library can not be executed and thus it does not have any entry point.

What are the differences between a .NET Assembly, a Windows DLL and a COM Component?

A Windows DLL contains library code to be used by any program running on Windows. A DLL may contain either structured or object oriented libraries.

COM (Component Object Model) is the component model based on the object oriented design, which means that the components represented by the COM component exists in the form of classes and objects implementing a standard specification defined by COM. COM components can be used by any program running on Windows Operating System; be it is written with VB, C++, Java or even some .NET compliant language like C# and VB.NET.

Dot NET assembly is the component standard specified by the .NET. Hence, dot net assemblies are understandable to only Microsoft.NET and can be used only in .NET managed applications.

What is the difference between traditional development and .NET development?

In traditional programming languages, the source code of a program is compiled to a specific platform’s assembly language and then machine language code. Later the library code required by the program is linked to it. Finally the operating system executes the program when desired by the user. The complete process is depicted in the following figure



In the presence of dot net framework, a program is not compiled to the native machine executable code; rather it gets compiled to an intermediate language code called Microsoft Intermediate Language (MSIL) or Common Intermediate Language (CIL). The Dot Net Common Language Runtime (CLR) then converts this intermediate code at runtime to the machine executable code. The optimization is carried out at runtime. A program also does not call the operating system APIs directly; rather it delegates this task to the CLR which performs the desired operations on behalf of the program and returns the results of the operations back to the program. The CLR also performs the memory management, garbage collection, security and thread management on behalf of the program. Dot NET framework is shipped with the supporting object oriented framework of common code libraries, called the .NET Framework Class Library (FCL), to facilitate the common operations. Hence the .Net manages the overall execution of an application. This is the reason why the code running on .Net framework is sometimes called the managed code. The complete process is depicted in the following Figure. Note that only the CLR (and thus the .Net framework and not the user application) is interacting and coupled with the platform and operating system.

What about the MS.NET standardization?

Microsoft has secured certification for both C# and CLI from ECMA and ISO/IEC as Industry standards. This is a very important step for Microsoft and .Net platform because this enhances the credibility of the newer .Net platform and allures a larger portion of technology industry into adopting .Net as their development platform. Several companies and government organizations only utilize ISO certified technologies; for example, in Australia anything ISO certified is also considered Australian standard according to the rules of the Australian government. Several academic institutions will now be interested in teaching standard C#. Another major outcome of having an open industry standard specification is .Net platform could be getting ported to other platforms like Linux and UNIX; best example is the Mono Project by Ximian- it is an open source implementation of .Net platform for UNIX and Linux based on ECMA approved Public Domain Specification of C# and CLI.

Microsoft submitted the specifications to ECMA, which in turn fast-tracked them through ISO. In doing so, Microsoft released all intellectual property in the core C#/CLI platform to the public domain. No one needs a license to implement C#/CLI. This will also help everybody in better understanding the implementations of C# and CLI which are at the core of .Net platform. However, the whole of .Net platform is not a Public domain standard- Microsoft still owns complete Intellectual property rights to several class libraries and API within the .Net platform.

Are old projects created in Visual Studio .NET 2002 or 2003 supported in Visual Studio 2005?

Old projects will continue to run without change. In Visual Studio 2005, if you open a project created in Visual Studio .NET 2002 or 2003, the project is converted to the new project layout used in Visual Studio 2005. As part of the conversion, pages that use the old code-behind model are converted to use the new code-behind model. You cannot create pages using the old code-behind model in Visual Studio 2005.

Can I have VS.NET and the Visual Studio 6.0 installed on the same machine?

Yes! VS.Net works with the .Net framework, while VS6.0 works with MFC or the Windows API directly, for the most part. They can be installed and run on the same machine without any considerations.

Why are Server control tags shown in the browser instead of the controls it represents?

This is because the server control tags were not converted into their respecting HTML element tags by ASP.Net. This happens when ASP.Net is not properly registered with IIS. .Net framework provides an Administration utility that manages the installation and uninstallation of multiple versions of ASP.NET on a single machine. You can find the file in C:\WINNT\Microsoft.NET\Framework\v**\aspnet_regiis.exe use the command: aspnet_regiis.exe -u ---> to uninstall current asp.net version. Use the command: aspnet_regiis.exe -i ---> to install current asp.net version

DOT NET - FAQ

DOT NET - Frequently Asked Question

1. What is the .NET Framework?

.NET is a general-purpose software development platform, similar to Java. At its core is a virtual machine that turns intermediate language (IL) into machine code. High-level language compilers for C#, VB.NET and C++ are provided to turn source code into IL. An extensive class library is included, featuring all the functionality one might expect from a contempory development platform - windows GUI development (Windows Forms), database access (ADO.NET), web development (ASP.NET), web services, XML etc.

2. Explain why tracing helps with exception handling.

Tracing allows you to record unusual events while your application is running, without users being aware of it. If an unanticipated exception occurs, your application can write a message to the trace log, which helps you diagnose problems during testing and after deployment.

3. What is the common language runtime (CLR)?

The common language runtime manages memory, thread execution, code execution, code safety verification, compilation, and other system services. These features are intrinsic to the managed code that runs on the common language runtime

 

The runtime also accelerates developer productivity.

The runtime is designed to enhance performance.

The runtime can be hosted by high-performance, server-side applications, such as Microsoft® SQL Server™ and Internet Information Services (IIS).

 

4. What is the Microsoft Intermediate Language (MSIL)?

IL = Intermediate Language. Also known as MSIL (Microsoft Intermediate Language) or CIL (Common Intermediate Language). All .NET source code (of any language) is compiled to IL during development. The IL is then converted to machine code at the point where the software is installed, or (more commonly) at run-time by a Just-In-Time (JIT) compiler. MSIL allows for true cross-language integration.

 

5. How do assemblies find each other?

By searching directory paths. There are several factors, which can affect the path (such as the AppDomain host, and application configuration files), but for private assemblies the search path is normally the application's directory and its sub-directories. For shared assemblies, the search path is normally same as the private assembly path plus the shared assembly cache.

 

6. What are private assemblies and shared assemblies?

Location and visibility: A private assembly is normally used by a single application, and is stored in the application's directory, or a sub-directory beneath. A shared assembly is normally stored in the global assembly cache, which is a repository of assemblies maintained by the .NET runtime. Shared assemblies are usually libraries of code which many applications will find useful, e.g. the .NET framework classes.
Versioning: The runtime enforces versioning constraints only on shared assemblies, not on private assemblies.

7. How can I produce an assembly?

The simplest way to produce an assembly is directly from a .NET compiler. You can then view the contents of the assembly by running the "IL Disassembler" tool that comes with the .NET SDK.
Alternatively you can compile your source into modules, and then combine the modules into an assembly using the assembly linker (al.exe). For the C# compiler, the /target: module switch is used to generate a module instead of an assembly.

 

8. What is managed code and managed data?

Managed code: The .NET framework provides several core run-time services to the programs that run within it - for example exception handling and security. For these services to work, the code must provide a minimum level of information to the runtime. Such code is called managed code.

Managed data: This is data that is allocated and freed by the .NET runtime's garbage collector.
Managed code is code that is written to target the services of the common language runtime. In order to target these services, the code must provide a minimum level of information (metadata) to the runtime. All C#, Visual Basic .NET, and JScript .NET code is managed by default. Visual Studio .NET C++ code is not managed by default, but the compiler can produce managed code by specifying a command-line switch (/CLR).
Closely related to managed code is managed data—data that is allocated and de-allocated by the common language runtime's garbage collector. C#, Visual Basic, and JScript .NET data is managed by default. C# data can, however, be marked as unmanaged through the use of special keywords. Visual Studio .NET C++ data is unmanaged by default (even when using the /CLR switch), but when using Managed Extensions for C++, a class can be marked as managed by using the __gc keyword. As the name suggests, this means that the memory for instances of the class is managed by the garbage collector. In addition, the class becomes a full participating member of the .NET Framework community, with the benefits and restrictions that brings. An example of a benefit is proper interoperability with classes written in other languages (for example, a managed C++ class can inherit from a Visual Basic class). An example of a restriction is that a managed class can only inherit from one base class.

 

9. How does assembly versioning work?

Each assembly has a version number called the compatibility version. Also each reference to an assembly (from another assembly) includes both the name and version of the referenced assembly.
The version number has four numeric parts (e.g. 5.5.2.33). Assemblies with either of the first two parts different are normally viewed as incompatible. If the first two parts are the same, but the third is different, the assemblies are deemed as 'maybe compatible'. If only the fourth part is different, the assemblies are deemed compatible. However, this is just the default guideline - it is the version policy that decides to what extent these rules are enforced. The version policy can be specified via the application configuration file.
Remember: versioning is only applied to shared assemblies, not private assemblies.

10. What is garbage collection?

Garbage collection is a mechanism that allows the computer to detect when an object can no longer be accessed. It then automatically releases the memory used by that object (as well as calling a clean-up routine, called a "finalizer," which is written by the user). Some garbage collectors like the one used by .NET, compact memory and therefore decrease your program's working set.

11. What operating systems does the .NET Framework run on?

The runtime supports Windows Server 2003, Windows XP, Windows 2000, NT4 SP6a and Windows ME/98. Windows 95 is not supported. Some parts of the framework do not work on all platforms - for example, ASP.NET is only supported on XP and Windows 2000/2003. Windows 98/ME cannot be used for development.
IIS is not supported on Windows XP Home Edition, and so cannot be used to host ASP.NET. However, the ASP.NET Web Matrix web server does run on XP Home. The .NET Compact Framework is a version of the .NET Framework for mobile devices, running Windows CE or Windows Mobile.

12. What is Namespace?

It gives you a way to organize your classes, so that related classes are bound together in a namespace.
It helps in large applications where different classes may be provided by different people, different teams, or even different organizations. Avoiding name clashes in large applications can be quite a headache, and in the past, developers have resorted to arcane naming conventions to ensure uniqueness for their class names.

13. Explain why exception handling is important to a completed application.

When an unhandled exception occurs in an application, the application stops—the user can't proceed, and any work he or she did immediately prior to the exception is lost. Exception handling provides a way to intercept and correct unusual occurrences that would otherwise cause these problems.

14. Describe the purpose of error pages and why they are needed.

Because Web applications run over the Internet, some exceptions occur outside the scope of the application. This means that your application can't respond directly to these exceptions. These types of exceptions are identified by HTTP response codes, which IIS can respond to by displaying custom error pages listed in your application's Web.config file.

15. Explain why tracing helps with exception handling.

Tracing allows you to record unusual events while your application is running, without users being aware of it. If an unanticipated exception occurs, your application can write a message to the trace log, which helps you diagnose problems during testing and after deployment.

16. What is a Repeater control?

Repeater control is a data-bound list control that allows custom layout by repeating a specified template for each item displayed in the list. It does not have built-in layout or styles, developers are required to explicitly declare HTML layout, formatting and style tags within the control's templates.

Frequently Asked Question - DOT NET Interview Top Questions

1.      So can a COM object talk to a .NET object?

Yes, through Runtime Callable Wrapper (RCW) or PInvoke.

2.      Describe the advantages of writing a managed code application instead of unmanaged one. What's involved in certain piece of code being managed?

The advantages include automatic garbage collection, memory management, support for versioning and security. These advantages are provided through .NET FCL and CLR, while with the unmanaged code similar capabilities had to be implemented through third-party libraries or as a part of the application itself.

3.      Are COM objects managed or unmanaged?

Since COM objects were written before .NET, apparently they are unmanaged. Any code not written in the Microsoft .NET framework environment is UNMANAGED. So naturally COM+ is unmanaged because it is written in Visual Basic 6

4.      How do you generate an RCW from a COM object?

Use the Type Library Import utility shipped with SDK. tlbimp COMobject.dll /out:.NETobject.dll or reference the COM library from Visual Studio in your project.

5.      I can't import the COM object that I have on my machine.

Did you write that object? You can only import your own objects. If you need to use a COM component from another developer, you should obtain a Primary Interop Assembly (PIA) from whoever authored the original object.

6.      How do you call unmanaged methods from your .NET code through PInvoke?

Supply a DllImport attribute. Declare the methods in your .NET code as static extern. Do not implement the methods as they are implemented in your unmanaged code, you're just providing declarations for method signatures.

7.      Can you retrieve complex data types like structs from the PInvoke calls?

Yes, just make sure you re-declare that struct, so that managed code knows what to do with it.

8.      I want to expose my .NET objects to COM objects. Is that possible?

Yes, but few things should be considered first. Classes should implement interfaces explicitly. Managed types must be public. Methods, properties, fields, and events that are exposed to COM must be public. Types must have a public default constructor with no arguments to be activated from COM. Types cannot be abstract.

9.      Suppose I call a COM object from a .NET application, but COM object throws an error. What happens on the .NET end?

COM methods report errors by returning HRESULTs; .NET methods report them by throwing exceptions. The runtime handles the transition between the two. Each exception class in the .NET Framework maps to an HRESULT.

10. Can you inherit a COM class in a .NET application?

The .NET Framework extends the COM model for reusability by adding implementation inheritance. Managed types can derive directly or indirectly from a COM class; more specifically, they can derive from the runtime callable wrapper generated by the runtime. The derived type can expose all the method and properties of the COM object as well as methods and properties implemented in managed code. The resulting object is partly implemented in managed code and partly implemented in unmanaged code.

11. Suppose I call a COM object from a .NET application, but COM object throws an error. What happens on the .NET end?

COM methods report errors by returning HRESULTs; .NET methods report them by throwing exceptions. The runtime handles the transition between the two. Each exception class in the .NET Framework maps to an HRESULT.

12. What is RCW (Run time Callable Wrappers)?

The common language runtime exposes COM objects through a proxy called the runtime callable wrapper (RCW). Although the RCW appears to be an ordinary object to .NET clients, its primary function is to marshal calls between a .NET client and a COM object.

13. What is CCW (COM Callable Wrapper)

A proxy object generated by the common language runtime so that existing COM applications can use managed classes, including .NET Framework classes, transparently.