.NET Interview Questions

             








1. What is the difference between ASP.Net and VB.NET?
ASP.Net is an “environment”, and VB.Net is a programming language. You can write ASP.Net pages (called “Web Forms” by Microsoft) using VB.Net (or C#, or J# or Managed C++ or any one of a number of .Net compatible languages).

2. What base class do all Forms inherit from?
System.Windows.Forms.Form

3. What is the difference between Debug.Write and Trace.Write? When should each be used?
The Debug.Write call won’t be compiled when the DEBUG symbol is not defined (when doing a release build). Trace.Write calls will be compiled. Debug.Write is for information you want only in debug builds, Trace.Write is for final realease

4. Can you give an example of when it would be appropriate to use a web service as opposed to non-serviced .NET component?
Web service is one of main component in Service Oriented Architecture. You could use web services when your clients and servers are running on different networks and also different platforms. This provides a loosely coupled architecture.

5. Is it possible to restrict the scope/field method of a class to the classes in the same name space?
There is no way to restrict to a namespace. Namespaces are never units of protection. But if you’re using assemblies, you can use the ‘internal’ access modifier to restrict access to only within the assembly.

6. What is the equivalent of exit () for quitting in .NET application?
You can use System.Environment.Exit(int exitCode) to exit the application or Application.Exit() if it’s a Windows Forms app.

7. Is there regular expression (regex) support available to c# developers?
Yes. The .NET class libraries provide support for regular expressions. Look at the System.Text.RegularExpressions namespace.

8. How many types of validation controls are supported in ASP.NET?
RequiredField Validator Control,Range Validator Control, RegularExpression Validator Control,Custom Validator Control and Validation Summary Control are provided by ASP.NET.

9. What is Tracing in ASP.NET?
ASP.NET introduces new functionality that allows you to write debug statements, directly in your code, without having to remove them from your application when it is deployed to production servers. Called tracing, this feature allows you to write variables or structures in a page, assert whether a condition is met, or simply trace through the code.

10. What exactly happens when aspx page is requested from Browser?
At its core, the ASP.NET execution engine compiles the page into a class, which derives from the code behind class (which in turn derives directly or indirectly from the Page class). Then it injects the newly created class into the execution environment, instantiates it, and executes it.

11. Methods of Deployment:
You can deploy an ASP.NET Web application using any one of the following three deployment options

• 1.XCOPY Deployment
• 2.Using the Copy Project option in VS .NET
• 3.Deployment using VS.NET installer

12. What can be stored in Web.config file?
There are number of important settings that can be stored in the configuration file. Here are some of the most frequently used configurations, stored conveniently inside Web.config file..

• 1. Database connections
• 2. Session States
• 3. Error Handling4. Security

13. Is String a value type of Reference Type?string is actually ref Type but some difference with other ref objectValue type - bool, byte, chat, decimal, double, enum , float, int, long, sbyte, short,strut, uint, ulong, ushortValue types are stored in the StackReference type - class, delegate, interface, object, stringReference types are stored in the Heap

14. What is the purpose of garbage Collection?
The purpose of Garge collection is to identify and discard objects that are no longer needed by a program so that their resources may be reclaimed and reused.

15. What does AspCompat=”true” mean and when should I use it?
AspCompat is an aid in migrating ASP pages to ASPX pages. It defaults to false but should be set to true in any ASPX file that creates apartment-threaded COM objects–that is, COM objects registered ThreadingModel=Apartment. That includes all COM objects written with Visual Basic 6.0.




16. Code to Export DataGrid to Excel in web application
Response.Clear();
Response.Buffer true;
Response.ContentType "application/vnd.ms-excel";
Response.AddHeader("Content-Disposition" "attachment;filename ReviewDesignation.xls");//This lets you always open the Excel window when exporting whether you click on open or save.
Response.Charset "";
this.EnableViewState false;
System.IO.StringWriter oStringWriter new
System.IO.StringWriter();System.Web.UI.HtmlTextWriter oHtmlTextWriter
new System.Web.UI.HtmlTextWriter(oStringWriter);
this.ClearControls(dGrid);
dGrid.RenderControl(oHtmlTextWriter);
Response.Write(oStringWriter.ToString());
Response.End();


17. What debugging tools come with the .NET SDK?
A. CorDBG – command-line debugger. To use CorDbg, you must compile the original C# file using the /debug switch.
B. DbgCLR – graphic debugger. Visual Studio .NET uses the DbgCLR.


18. What does assert() method do?
In debug compilation, assert takes in a Boolean condition as a parameter, and shows the error dialog if the condition is false. The program proceeds without any interruption if the condition is true.


19. What’s the difference between the Debug class and Trace class?
Documentation looks the same. Use Debug class for debug builds, use Trace class for both debug and release builds.

20. What are the different ways a method can be overloaded?
Different parameter data types, different number of parameters, different order of parameters


21. Is XML case-sensitive?
Yes

22. What does the keyword “virtual” declare for a method or property?
The method or property can be overridden.


23. What is a satellite assembly?
When you write a multilingual or multi-cultural application in .NET, and want to distribute the core application separately from the localized modules, the localized assemblies that modify the core application are called satellite assemblies.


24. What is the smallest unit of execution in .NET?
an Assembly

25. How do you convert a value-type to a reference-type?
Use Boxing.


26. What does the term immutable mean?
Immutable means you can't change the currrent data, but if you perform some operation on that data, a new copy is created. The operation doesn't change the data itself. Like let's say you have a string object having "hello" value. Now if you say temp = temp + "new value" a new object is created, and values is saved in that. the temp object is immutable, and can't be changed.


27. Does Array.CopyTo make a deep copy?
No


28. What is the difference between Server.Transfer and Response.Redirect? Why would I choose one over the other?
 Server.Trnasfer will prevent round trip. it will redirect pages which or in the same directory. NO way to pass the query strings . Thru http context we can able to get the previous page control values.

Response.Redirect : There is a round trip to process the request. We can redirect to any page external / internal other than aspx. We can pass the query string thru which we can manage sessions.


29. Explain the differences between Server-side and Client-side code?
 Server side code will execute at server end all the business logic will execute at server end where as client side code will execute at client side at browser end.

30. How does VB.NET/C# achieve polymorphism?
 Function overloading.
Operator overloading




31. Write a simple Windows Forms MessageBox
Statement: System.Windows.Forms.MessageBox.Show("Hello, Windows Forms");

32. Can you write a class without specifying namespace? Which namespace does it belong to by default??
Yes, you can, then the class belongs to global namespace which has no name. For commercial products, naturally, you wouldn’t want global namespace.

33. You are designing a GUI application with a window and several widgets on it. The user then resizes the app window and sees a lot of grey space, while the widgets stay in place. What’s the problem?
One should use anchoring for correct resizing. Otherwise the default property of a widget on a form is top-left, so it stays at the same location when resized.

34. How can you save the desired properties of Windows Forms application?.
config files in .NET are supported through the API to allow storing and retrieving information. They are nothing more than simple XML files, sort of like what .ini files were before for Win32 apps.

35. So how do you retrieve the customized properties of a .NET application from XML .config file?
Initialize an instance of AppSettingsReader class. Call the GetValue method of AppSettingsReader class, passing in the name of the property and the type expected. Assign the result to the appropriate variable.

36. Can you automate the process in Visual Studio ?Yes, use Dynamic Properties for automatic .config creation, storage and retrieval.

37. My progress bar freezes up and dialog window shows blank, when an intensive background process takes over.
Yes, you should’ve multi-threaded your GUI, with taskbar and main form being one thread, and the background process being the other.

38. What’s the safest way to deploy a Windows Forms app?
Web deployment: the user always downloads the latest version of the code; the program runs within security sandbox, properly written app will not require additional security privileges.

39. Why is it not a good idea to insert code into InitializeComponent method when working with Visual Studio?
The designer will likely throw it away; most of the code inside InitializeComponent is auto-generated.

40. What’s the difference between WindowsDefaultLocation and WindowsDefaultBounds?
WindowsDefaultLocation tells the form to start up at a location selected by OS, but with internally specified size. WindowsDefaultBounds delegates both size and starting position choices to the OS.

41. What’s the difference between Move and LocationChanged? Resize and SizeChanged?
Both methods do the same, Move and Resize are the names adopted from VB to ease migration to C#.

42. How would you create a non-rectangular window, let’s say an ellipse?
Create a rectangular form, set the TransparencyKey property to the same value as BackColor, which will effectively make the background of the form transparent. Then set the FormBorderStyle to FormBorderStyle.None, which will remove the contour and contents of the form.

43. How do you create a separator in the Menu Designer?
A hyphen ‘-’ would do it. Also, an ampersand ‘&\’ would underline the next letter.

44. How’s anchoring different from docking?
Anchoring treats the component as having the absolute size and adjusts its location relative to the parent form. Docking treats the component location as absolute and disregards the component size. So if a status bar must always be at the bottom no matter what, use docking. If a button should be on the top right, but change its position with the form being resized, use anchoring.




45.What’s a Windows process?
It’s an application that’s running and had been allocated memory.

46.What’s typical about a Windows process in regards to memory allocation?
Each process is allocated its own block of available RAM space, no process can access another process’ code or data. If the process crashes, it dies alone without taking the entire OS or a bunch of other applications down.

47.Why do you call it a process? What’s different between process and application in .NET, not common computer usage, terminology?
A process is an instance of a running application. An application is an executable on the hard drive or network. There can be numerous processes launched of the same application (5 copies of Word running), but 1 process can run just 1 application.

48.What distributed process frameworks outside .NET do you know?
Distributed Computing Environment/Remote Procedure Calls (DEC/RPC), Microsoft Distributed Component Object Model (DCOM), Common Object Request Broker Architecture (CORBA), and Java Remote Method Invocation (RMI).

49.What are possible implementations of distributed applications in .NET?
.NET Remoting and ASP.NET Web Services. If we talk about the Framework Class Library, noteworthy classes are in System.Runtime.Remoting and System.Web.Services.

50.When would you use .NET Remoting and when Web services?
Use remoting for more efficient exchange of information when you control both ends of the application. Use Web services for open-protocol-based information exchange when you are just a client or a server with the other end belonging to someone else.

51.What’s a proxy of the server object in .NET Remoting?
It’s a fake copy of the server object that resides on the client side and behaves as if it was the server. It handles the communication between real server object and the client object. This process is also known as marshaling.

52.What are remotable objects in .NET Remoting?
Remotable objects are the objects that can be marshaled across the application domains. You can marshal by value, where a deep copy of the object is created and then passed to the receiver. You can also marshal by reference, where just a reference to an existing object is passed.

53.What are channels in .NET Remoting?
Channels represent the objects that transfer the other serialized objects from one application domain to another and from one computer to another, as well as one process to another on the same box. A channel must exist before an object can be transferred.

54.What security measures exist for .NET Remoting in System.Runtime.Remoting?
None. Security should be taken care of at the application level. Cryptography and other security techniques can be applied at application or server level.

55.What is a formatter?
A formatter is an object that is responsible for encoding and serializing data into messages on one end, and deserializing and decoding messages into data on the other end.
Choosing between HTTP and TCP for protocols and Binary and SOAP for formatters, what are the trade-offs?
Binary over TCP is the most effiecient, SOAP over HTTP is the most interoperable.

56.What’s SingleCall activation mode used for?
If the server object is instantiated for responding to just one single request, the request should be made in SingleCall mode.

57.What’s Singleton activation mode?
A single object is instantiated regardless of the number of clients accessing it. Lifetime of this object is determined by lifetime lease.

58.How do you define the lease of the object?
By implementing ILease interface when writing the class code.

59.Can you configure a .NET Remoting object via XML file?
Yes, via machine.config and application level .config file (or web.config in ASP.NET). Application-level XML settings take precedence over machine.config.

60.How can you automatically generate interface for the remotable object in .NET with Microsoft tools?
Use the Soapsuds tool.




61. What’s the implicit name of the parameter that gets passed into the class’ set method?
Value, and its datatype depends on whatever variable we’re changing.

62. How do you inherit from a class in C#?
Place a colon and then the name of the base class. Notice that it’s double colon in C++.

63. Does C# support multiple inheritance?
No, use interfaces instead.


64. When you inherit a protected class-level variable, who is it available to?
Classes in the same namespace.


65. Are private class-level variables inherited?
Yes, but they are not accessible, so looking at it you can honestly say that they are not inherited. But they are.


66. Describe the accessibility modifier protected internal.
It’s available to derived classes and classes within the same Assembly (and naturally from the base class it’s declared in).


67. C# provides a default constructor for me.
I write a constructor that takes a string as a parameter, but want to keep the no parameter one. 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.


68. What’s the top .NET class that everything is derived from?
System.Object.

69. How’s method overriding different from overloading?
When overriding, you change the method behavior for a derived class. Overloading simply involves having a method with the same name within the class.


70. What does the keyword virtual mean in the method definition?
The method can be over-ridden.


71. Can you declare the override method static while the original method is non-static?
No, you can’t, the signature of the virtual method must remain the same, only the keyword virtual is changed to keyword override.


72. Can you override private virtual methods?
No, moreover, you cannot access private methods in inherited classes, have to be protected in the base class to allow any sort of access.

73. Can you prevent your class from being inherited and becoming a base class for some other classes?
Yes, that’s what keyword sealed in the class definition is for. The developer trying to derive from your class will get a message: cannot inherit from Sealed class WhateverBaseClassName. It’s the same concept as final class in Java.


74. Can you allow class to be inherited, but prevent the method from being over-ridden?
Yes, just leave the class public and make the method sealed.

75. What’s an abstract class?
A class that cannot be instantiated. A concept in C++ known as pure virtual method. A class that must be inherited and have the methods over-ridden. Essentially, it’s a blueprint for a class without any implementation.




76. When do you absolutely have to declare a class as abstract (as opposed to free-willed educated choice or decision based on UML diagram)?
When at least one of the methods in the class is abstract. When the class itself is inherited from an abstract class, but not all base abstract methods have been over-ridden.

77. What’s an interface class?
It’s an abstract class with public abstract methods all of which must be implemented in the inherited classes.


78. 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.


79. Can you inherit multiple interfaces?
Yes, why not.

80. 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.

81. What’s the difference between an interface and abstract class?
In the interface all methods must be abstract; in the abstract class some methods can be concrete. In the interface no accessibility modifiers are allowed, which is ok in abstract classes.


82. How can you overload a method?
Different parameter data types, different number of parameters, different order of parameters.


83. If a base class has a bunch of overloaded constructors, and an inherited class has another bunch of overloaded constructors, can you enforce a call from an inherited constructor to an arbitrary 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.


84. 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.


85. What’s the advantage of using System.Text.StringBuilder over System.String?
StringBuilder is more efficient in the cases, where a lot of manipulation is done to the text. Strings are immutable, so each time it’s being operated on, a new instance is created.


86. Can you store multiple data types in System.Array?
No.


87. What’s the difference between the System.Array.CopyTo() and System.Array.Clone()?
The first one performs a deep copy of the array, the second one is shallow.


88. How can you sort the elements of the array in descending order?
By calling Sort() and then Reverse() methods.


89. What’s the .NET datatype that allows the retrieval of data by a unique key?
HashTable.

89. What’s class SortedList underneath?
A sorted HashTable.




90. Will finally block get executed if the exception had not occurred?
Yes.

91. 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 {}.


92. 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.

93. 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.


94. What’s a delegate?
A delegate object encapsulates a reference to a method. In C++ they were referred to as function pointers.


95. What’s a multicast delegate?
It’s a delegate that points to and eventually fires off several methods.


96. How’s the DLL Hell problem solved in .NET?
Assembly versioning allows the application to specify not only the library it needs to run (which was available under Win32), but also the version of the assembly.


97. What are the ways to deploy an assembly?
An MSI installer, a CAB archive, and XCOPY command.


98. What’s a satellite assembly?
When you write a multilingual or multi-cultural application in .NET, and want to distribute the core application separately from the localized modules, the localized assemblies that modify the core application are called satellite assemblies.


99. What namespaces are necessary to create a localized application?

1. System.Globalization
2. System.Resources.


100. What’s the difference between // comments, /* */ comments and /// comments?
Single-line, multi-line and XML documentation comments.


101. How do you generate documentation from the C# file commented properly with a command-line compiler?
Compile it with a /doc switch.


102. What’s the difference between <> and <> XML documentation tag?
Single line code example and multiple-line code example.


103. Is XML case-sensitive?
Yes, so <> and <> are different elements.


104. What debugging tools come with the .NET SDK?
CorDBG – command-line debugger, and DbgCLR – graphic debugger. Visual Studio .NET uses the DbgCLR. To use CorDbg, you must compile the original C# file using the /debug switch.


105. What does the This window show in the debugger?
It points to the object that’s pointed to by this reference. Object’s instance data is shown.


106. What does assert() do?
In debug compilation, assert takes in a Boolean condition as a parameter, and shows the error dialog if the condition is false. The program proceeds without any interruption if the condition is true.


107. What’s the difference between the Debug class and Trace class?
Documentation looks the same. Use Debug class for debug builds, use Trace class for both debug and release builds.


108. Why are there five tracing levels in System.Diagnostics.TraceSwitcher?
The tracing dumps can be quite verbose and for some applications that are constantly running you run the risk of overloading the machine and the hard drive there. Five levels range from None to Verbose, allowing to fine-tune the tracing activities.


109. Where is the output of TextWriterTraceListener redirected?
To the Console or a text file depending on the parameter passed to the constructor.





110. How do you debug an ASP.NET Web application?
Attach the aspnet_wp.exe process to the DbgClr debugger.

111. What are three test cases you should go through in unit testing?
Positive test cases (correct data, correct output), negative test cases (broken or missing data, proper handling), exception test cases (exceptions are thrown and caught properly).

112. Can you change the value of a variable while debugging a C# application?
Yes, if you are debugging via Visual Studio.NET, just go to Immediate window.

113. Explain the three services model (three-tier application).
Presentation (UI), business (logic and underlying code) and data (from storage or other sources).

114. What are advantages and disadvantages of Microsoft-provided data provider classes in ADO.NET?
SQLServer.NET data provider is high-speed and robust, but requires SQL Server license purchased from Microsoft. OLE-DB.NET is universal for accessing other sources, like Oracle, DB2, Microsoft Access and Informix, but it’s a .NET layer on top of OLE layer, so not the fastest thing in the world. ODBC.NET is a deprecated layer provided for backward compatibility to ODBC engines.


115. What’s 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.

116. What is the wildcard character in SQL?
Let’s say you want to query database with LIKE for all employees whose name starts with La. The wildcard character is %, the proper query with LIKE would involve ‘La%’.

117. Explain ACID rule of thumb for transactions.
Transaction must be Atomic (it is one unit of work and does not dependent on previous and following transactions), Consistent (data is either committed or roll back, no “in-between” case where something has been updated and something hasn’t), Isolated (no transaction sees the intermediate results of the current transaction), Durable (the values persist if the data had been committed even if the system crashes right after).


118. What connections does Microsoft SQL Server support?
Windows Authentication (via Active Directory) and SQL Server authentication (via Microsoft SQL Server username and passwords).

119. Which one is trusted and which one is untrusted?
Windows Authentication is trusted because the username and password are checked with the Active Directory, the SQL Server authentication is untrusted, since SQL Server is the only verifier participating in the transaction.


120. Why would you use untrusted verificaion?
Web Services might use it, as well as non-Windows applications.

121. What does the parameter Initial Catalog define inside Connection String?
The database name to connect to.

122. What’s the data provider name to connect to Access database?
Microsoft.Access.

123. What does Dispose method do with the connection object?
Deletes it from the memory.

124. What is a pre-requisite for connection pooling?
Multiple processes must agree that they will share the same connection, where every parameter is the same, including the security settings.

125. Briefly describe the major components of the .NET Framework and describe what each component does?

 The .NET Framework consists of two primary parts: the Common language runtime, which manages application execution, enforces type safety, and manages memory reclamation, and the .NET base class library, which consists of thousands of predeveloped classes that can be used to build applications.

126. Briefly explains what is meant by a reference type and a value type?

A value type holds all of the data represented by the variable within the variable itself. A reference type contains a reference to a memory address that holds the data instead of the actual data itself.

127. How do you enable your application to use .NET base class library members without referencing their fully qualified names?

Use the Imports keyword (VB.NET) or the Using keyword(Visual c#) to make a .NET framework namespace visible to your application.

128. Briefly describe how the garbage collection works?

The garbage collector is a thread that runs in the background of managed .NET applications. It constantly traces the reference tree and attempts to find objects that are no longer referenced. When a non referenced object is found, its memory is reclaimed for later use.

129. Briefly describe what members are, and list the four types of members?

 Members are the part s of a class or a structure that hold data or implement functionality. The primary member types are fields, properties, methods and events.

130. Explain what constructors and destructors are and describe what they are used for?

The constructor is the method that initializes a class or structure and is run when a type is first instantiated. It is used to set default values and perform other tasks required by the class. A destructor is the method that is run as the object is being reclaimed by garbage collection. It contains any code that is required for cleanup of the object.

131. Do you need to instantiate a class before accessing a shared (static) member> Why or Why not?

Because a Shared (static) member belongs to the type rather than to any instance of the type, you can access the member without first creating an instance of the type.

132. Briefly describe how a class is similar to a structure. How are they different?

Both classes and structures can have members such as methods, properties and fields both use a constructor for initialization, and both inherit from System.Object. Both classes and structures can be used to model real-world objects. Classes are reference types, and the memory that holds class instances is allocated on the heap. Structures are value types, and the memory that holds structure instances is allocated on the stack.

133. You are writing an application that needs to display a common set of controls on several different forms. What is the fastest way to approach the problem?

Create a Single form that incorporates the common controls, and use visual inheritance to create derived forms.

134. What is an extender provider, and what does one do?

Extender providers are components that provide additional properties to controls on a form. Examples include the ErrorProvider, HelpProvider and ToolTip components. They can be used to provide additional information about particular controls to the user or the user in the user interface.