Top 100 .Net Interview Questions and Answer

.NET Interview Questions by Vineet Kumar Saini

Q1 - Write a query to find the total number of rows in a table

A1 - Select count(*) from t_employee;

Q2 - Write a query to eliminate duplicate records in the results of a table

A2 - Select distinct * from t_employee;

Q3 - Write a query to insert a record into a table

A3 - Insert into t_employee values ('empid35','Barack','Obama');

Q4 - Write a query to delete a record from a table

A4 - delete from t_employee where id='empid35';

Q5 - Write a query to display a row using index

A5 - For this, the indexed column of the table needs to be set as a parameter in the
where clause

select * from t_employee where id='43';

Q6 - Write a query to fetch the highest record in a table, based on a record,
say salary field in the t_salary table

A6 - Select max(salary) from t_salary;

Q7 - Write a query to fetch the first 3 characters of the field designation from
the table t_employee

A7 - Select substr(designation,1,3) from t_employee; -- Note here that the substr
function has been used.

Q8 - Write a query to concatenate two fields, say Designation and Department
belonging to a table t_employee

Select Designation + ‘ ‘ + Department from t_employee;

Q9 -What is the difference between UNION and UNION ALL in SQL?

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A9 - UNION is an SQL keyword used to merge the results of two or more tables
using a Select statement, containing the same fields, with removed duplicate
values. UNION ALL does the same, however it persists duplicate values.

Q10 - If there are 4 SQL Select statements joined using Union and Union All,
how many times should a Union be used to remove duplicate rows?

A10 - One time.

Q11 - What is the difference between IN and BETWEEN, that are used inside
a WHERE clause?

A11 - The BETWEEN clause is used to fetch a range of values, whereas the IN
clause fetches data from a list of specified values.

Q12 - Explain the use of the ‘LIKE’ keyword used in the WHERE
clause? Explain wildcard characters in SQL.

A12 - LIKE is used for partial string matches. The symbol ‘%’ ( for a string of any
character ) and ‘_’ (for any single character ) are the two wild card characters used
in SQL.

Q13 - What is the need to use a LIKE statement?

A13 - When a partial search is required in a scencario, where for instance, you
need to find all employees with the last name having the sequence of characters
"gat", then you may use the following query, to match a search criteria:

Select empid, firstname, lastname from t_employee where lastname like ‘%gats%’

This might search all employees with last name containing the character sequence
'gats' like Gates, Gatsby, Gatsburg, Sogatsky, etc.

% is used to represent remaining all characters in the name. This query fetches all
records contains gats in the e middle of the string.

Q14 - Explain the use of the by GROUP BY and the HAVING clause.

A14 - The GROUP BY partitions the selected rows on the distinct values of the
column on which the group by has been done. In tandem, the HAVING selects
groups which match the criteria specified.



Q15 - In a table t_employee, the department column is nullable. Write a query
to fetch employees which are not assigned a department yet.

A11. Select empid, firstname, lastname from t_employee where department is
null;

Q16 -What are the large objects supported by oracle and db2? What are the
large objects supported in MS SQL?

A16 - In Oracle and DB2 BLOB , CLOB ( Binary Large Objects, Character Large
Objects) are used.

In MS SQL - the data types are image and varbinary.

Q17 - Whats the capacity of the image data type in MS SQL?

A17 - Variable-length binary data with a maximum length of 2^31 - 1
(2,147,483,647) bytes.

Q18 - Whats the capacity of varbinary data type in MS SQL?

A18 - Variable-length binary data with a maximum length of 8,000 bytes.

Q19 - What’s the difference between a primary key and a unique key?

A19 - Both Primary key and Unique key enforce the uniqueness of a column on
which they are defined. However, a Primary key does not allow nulls, whereas
unique key allow nulls.

Q20 - What are the different types of joins in SQL?

INNER JOIN
OUTER JOIN
LEFT OUTER JOIN
RIGHT OUTER JOIN
FULL OUTER JOIN
INNER JOIN

Read here for more http://www.dotnetuncle.com/SQL/What-is-Join-in-SQL-types-
of-joins.aspx

Q21 - What is a Self join?



A21 - A join created by joining two or more instances of a same table.
Query: Select A.firstname ,B.firstname
from t_employee A, t_employee B
where A.supervisor_id = B.employee_id;

Q22 - What is a transaction and ACID?

A22 - Transaction - A transaction is a logical unit of work. All steps must be
committed or rolled back.
ACID - Atomicity, Consistency, Isolation and Durability, these are the unique
entities of a transaction.

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Short Answer .NET Interview Questions (PAGE 1)

Q1. Explain the differences between Server-side and Client-side code?
Ans. Server side code will execute at server (where the website is hosted) end, &
all the business logic will execute at server end where asclient side code will
execute at client side (usually written in javascript, vbscript, jscript) at browser
end.

Q2. What type of code (server or client) is found in a Code-Behind class?
Ans. Server side code.

Q3. How to make sure that value is entered in an asp:Textbox control?
Ans. Use a RequiredFieldValidator control.

Q4. Which property of a validation control is used to associate it with a server
control on that page?
Ans. ControlToValidate property.

Q5. How would you implement inheritance using VB.NET & C#?
Ans. C# Derived Class : Baseclass



VB.NEt : Derived Class Inherits Baseclass

Q6. Which method is invoked on the DataAdapter control to load the
generated dataset with data?
Ans. Fill() method.

Q7. What method is used to explicitly kill a user's session?
Ans. Session.Abandon()

Q8. What property within the asp:gridview control is changed to bind
columns manually?
Ans. Autogenerated columns is set to false

Q9. Which method is used to redirect the user to another page without
performing a round trip to the client?
Ans. Server.Transfer method.

Q10. How do we use different versions of private assemblies in same
application without re-build?
Ans.Inside the Assemblyinfo.cs or Assemblyinfo.vb file, we need to specify
assembly version.
assembly: AssemblyVersion

Q11. Is it possible to debug java-script in .NET IDE? If yes, how?
Ans. Yes, simply write "debugger" statement at the point where the breakpoint
needs to be set within the javascript code and also enable javascript debugging in
the browser property settings.

Q12. How many ways can we maintain the state of a page?
Ans. 1. Client Side - Query string, hidden variables, viewstate, cookies
2. Server side - application , cache, context, session, database

Q13. What is the use of a multicast delegate?
Ans. A multicast delegate may be used to call more than one method.

Q14. What is the use of a private constructor?
Ans. A private constructor may be used to prevent the creation of an instance for a
class.

Q15. What is the use of Singleton pattern?



Ans. A Singleton pattern .is used to make sure that only one instance of a class
exists.

Q16. When do we use a DOM parser and when do we use a SAX parser?
Ans. The DOM Approach is useful for small documents in which the program
needs to process a large portion of the document whereas the SAX approach is
useful for large documents in which the program only needs to process a small
portion of the document.

Q17. Will the finally block be executed if an exception has not occurred?
Ans.Yes it will execute.

Q18. What is a Dataset?
Ans. A dataset is an in memory database kindof object that can hold database
information in a disconnected environment.

Q19. Is XML a case-sensitive markup language?
Ans. Yes.

Q20. What is an .ashx file?
Ans. It is a web handler file that produces output to be consumed by an xml
consumer client (rather than a browser).

Q21. What is encapsulation?
Ans. Encapsulation is the OOPs concept of binding the attributes and behaviors in
a class, hiding the implementation of the class and exposing the functionality.

Q22. What is Overloading?
Ans. When we add a new method with the same name in a same/derived class but
with different number/types of parameters, the concept is called overluoad and this
ultimately implements Polymorphism.

Q23. What is Overriding?
Ans.When we need to provide different implementation in a child class than the
one provided by base class, we define the same method with same signatures in the
child class and this is called overriding.

Q24. What is a Delegate?



Ans. A delegate is a strongly typed function pointer object that encapsulates a
reference to a method, and so the function that needs to be invoked may be called
at runtime.

Q25. Is String a Reference Type or Value Type in .NET?
Ans. String is a Reference Type object.

Q26. What is a Satellite Assembly?
Ans. Satellite assemblies contain resource files corresponding to a locale (Culture
+ Language) and these assemblies are used in deploying an application globally for
different languages.

Q27. What are the different types of assemblies and what is their use?
Ans. Private, Public(also called shared) and Satellite Assemblies.

Q28. Are MSIL and CIL the same thing?
Ans. Yes, CIL is the new name for MSIL.

Q29. What is the base class of all web forms?
Ans. System.Web.UI.Page

Q30. How to add a client side event to a server control?
Ans. Example...
BtnSubmit.Attributes.Add("onclick","javascript:fnSomeFunctionInJavascript()");

Q31. How to register a client side script from code-behind?
Ans. Use the Page.RegisterClientScriptBlock method in the server side code to
register the script that may be built using a StringBuilder.

Q32. Can a single .NET DLL contain multiple classes?
Ans. Yes, a single .NET DLL may contain any number of classes within it.

Q33. What is DLL Hell?
Ans. DLL Hell is the name given to the problem of old unmanaged DLL's due to
which there was a possibility of version conflict among the DLLs.



Q34. can we put a break statement in a finally block?
Ans. The finally block cannot have the break, continue, return and goto statements.

Q35. What is a CompositeControl in .NET?
Ans. CompositeControl is an abstract class in .NET that is inherited by those web
controls that contain child controls within them.

Q36. Which control in asp.net is used to display data from an xml file and
then displayed using XSLT?
Ans. Use the asp:Xml control and set its DocumentSource property for associating
an xml file, and set its TransformSource property to set the xml control's xsl file
for the XSLT transformation.

Q37. Can we run ASP.NET 1.1 application and ASP.NET 2.0 application on
the same computer?
Ans. Yes, though changes in the IIS in the properties for the site have to be made
during deployment of each.

Q38. What are the new features in .NET 2.0?
Ans. Plenty of new controls, Generics, anonymous methods, partial classes,
iterators, property visibility (separate visibility for get and set) and static classes.

Q39. Can we pop a MessageBox in a web application?
Ans. Yes, though this is done clientside using an alert, prompt or confirm or by
opening a new web page that looks like a messagebox.

Q40. What is managed data?
Ans. The data for which the memory management is taken care by .Net runtime’s
garbage collector, and this includes tasks for allocation de-allocation.

Q41. How to instruct the garbage collector to collect unreferenced data?
Ans. We may call the garbage collector to collect unreferenced data by executing
the System.GC.Collect() method.



Q42. How can we set the Focus on a control in ASP.NET?
Ans. txtBox123.Focus(); OR Page.SetFocus(NameOfControl);

Q43. What are Partial Classes in Asp.Net 2.0?
Ans. In .NET 2.0, a class definition may be split into multiple physical files but
partial classes do not make any difference to the compiler as during compile time,
the compiler groups all the partial classes and treats them as a single class.

Q44. How to set the default button on a Web Form?
Ans. <asp:form id="form1" runat="server" defaultbutton="btnGo"/>

Q45.Can we force the garbage collector to run?
Ans. Yes, using the System.GC.Collect(), the garbage collector is forced to run in
case required to do so.

Q46. What is Boxing and Unboxing?
Ans. Boxing is the process where any value type can be implicitly converted to a
reference type object while Unboxing is the opposite of boxing process where the
reference type is converted to a value type.

Q47. What is Code Access security? What is CAS in .NET?
Ans. CAS is the feature of the .NET security model that determines whether an
application or a piece of code is permitted to run and decide the resources it can
use while running.

Q48. What is Multi-tasking?
Ans. It is a feature of operating systems through which multiple programs may run
on the operating system at the same time, just like a scenario where a Notepad, a
Calculator and the Control Panel are open at the same time.

Q49. What is Multi-threading?
Ans. When an application performs different tasks at the same time, the application
is said to exhibit multithreading as several threads of a process are running.2

Q50. What is a Thread?



Ans. A thread is an activity started by a process and its the basic unit to which an
operating system allocates processor resources.

Q51. What does AddressOf in VB.NET operator do?
Ans. The AddressOf operator is used in VB.NET to create a delegate object to a
method in order to point to it.

Q52. How to refer to the current thread of a method in .NET?
Ans. In order to refer to the current thread in .NET, the Thread.CurrentThread
method can be used. It is a public static property.

Q53. How to pause the execution of a thread in .NET?
Ans. The thread execution can be paused by invoking the
Thread.Sleep(IntegerValue) method where IntegerValue is an integer that
determines the milliseconds time frame for which the thread in context has to
sleep.

Q54. How can we force a thread to sleep for an infinite period?
Ans. Call the Thread.Interupt() method.

Q55. What is Suspend and Resume in .NET Threading?
Ans. Just like a song may be paused and played using a music player, a thread may
be paused using Thread.Suspend method and may be started again using the
Thread.Resume method. Note that sleep method immediately forces the thread to
sleep whereas the suspend method waits for the thread to be in a persistable
position before pausing its activity.

Q56. How can we prevent a deadlock in .Net threading?
Ans. Using methods like Monitoring, Interlocked classes, Wait handles, Event
raising from between threads, using the ThreadState property.

Q57. What is Ajax?
Ans. AsyncronousJavascript and XML - Ajax is a combination of client side
technologies that sets up asynchronous communication between the user interface
and the web server so that partial page rendering occur instead of complete page



postbacks.

Q58. What is XmlHttpRequest in Ajax?
Ans. It is an object in Javascript that allows the browser to communicate to a web
server asynchronously without making a postback.

Q59. What are the different modes of storing an ASP.NET session?
Ans. InProc (the session state is stored in the memory space of the Aspnet_wp.exe
process but the session information is lost when IIS reboots), StateServer (the
Session state is serialized and stored in a separate process call Viewstate is an
object in .NET that automatically persists control setting values across the multiple
requests for the same page and it is internally maintained as a hidden field on the
web page though its hashed for security reasons.

Q60. What is a delegate in .NET?
Ans. A delegate in .NET is a class that can have a reference to a method, and this
class has a signature that can refer only those methods that have a signature which
complies with the class.

Q61. Is a delegate a type-safe functions pointer?
Ans. Yes

Q62. What is the return type of an event in .NET?
Ans. There is No return type of an event in .NET.

Q63. Is it possible to specify an access specifier to an event in .NET?
Ans. Yes, though they are public by default.

Q64. Is it possible to create a shared event in .NET?
Ans. Yes, but shared events may only be raised by shared methods.

Q65. How to prevent overriding of a class in .NET?
Ans. Use the keyword NotOverridable in VB.NET and sealed in C#.

Q66. How to prevent inheritance of a class in .NET?



Ans. Use the keyword NotInheritable in VB.NET and sealed in C#.

Q67. What is the purpose of the MustInherit keyword in VB.NET?
Ans. MustInherit keyword in VB.NET is used to create an abstract class.

Q68. What is the access modifier of a member function of in an Interface
created in .NET?
Ans. It is always public, we cant use any other modifier other than the public
modifier for the member functions of an Interface.

Q69. What does the virtual keyword in C# mean?
Ans. The virtual keyword signifies that the method and property may be
overridden.

Q70. How to create a new unique ID for a control?
Ans. ControlName.ID = "ControlName" + Guid.NewGuid().ToString(); //Make
use of the Guid class

Q71A. What is a HashTable in .NET?
Ans. A Hashtable is an object that implements the IDictionary interface, and can be
used to store key value pairs. The key may be used as the index to access the
values for that index.

Q71B. What is an ArrayList in .NET?
Ans. Arraylist object is used to store a list of values in the form of a list, such that
the size of the arraylist can be increased and decreased dynamically, and moreover,
it may hold items of different types. Items in an arraylist may be accessed using an
index.

Q72. What is the value of the first item in an Enum? 0 or 1?
Ans. 0

Q73. Can we achieve operator overloading in VB.NET?
Ans. Yes, it is supported in the .NET 2.0 version, the "operator" keyword is used.



Q74. What is the use of Finalize method in .NET?
Ans. .NET Garbage collector performs all the clean up activity of the managed
objects, and so the finalize method is usually used to free up the unmanaged
objects like File objects, Windows API objects, Database connection objects, COM
objects etc.

Q75. How do you save all the data in a dataset in .NET?
Ans. Use the AcceptChanges method which commits all the changes made to the
dataset since last time Acceptchanges was performed.

Q76. Is there a way to suppress the finalize process inside the garbage
collector forcibly in .NET?
Ans. Use the GC.SuppressFinalize() method.

Q77. What is the use of the dispose() method in .NET?
Ans. The Dispose method in .NET belongs to IDisposable interface and it is best
used to release unmanaged objects like File objects, Windows API objects,
Database connection objects, COM objects etc from the memory. Its performance
is better than the finalize() method.

Q78. Is it possible to have have different access modifiers on the get and set
methods of a property in .NET?
Ans. No we can not have different modifiers of a common property, which means
that if the access modifier of a property's get method is protected, and it must be
protected for the set method as well.

Q79. In .NET, is it possible for two catch blocks to be executed in one go?
Ans. This is NOT possible because once the correct catch block is executed then
the code flow goes to the finally block.

Q80. Is there any difference between System.String and System.StringBuilder
classes?
Ans. System.String is immutable by nature whereas System.StringBuilder can have
a mutable string in which plenty of processes may be performed.



Q81. What technique is used to figure out that the page request is a postback?
Ans. The IsPostBack property of the page object may be used to check whether the
page request is a postback or not. IsPostBack property is of the type Boolean.

Q82. Which event of the ASP.NET page life cycle completely loads all the
controls on the web page?
Ans. The Page_load event of the ASP.NET page life cycle assures that all controls
are completely loaded. Even though the controls are also accessible in Page_Init
event but here, the viewstate is incomplete.

Q83. How is ViewState information persisted across postbacks in an
ASP.NET webpage?
Ans. Using HTML Hidden Fields, ASP.NET creates a hidden field with an
ID="__VIEWSTATE" and the value of the page's viewstate is encoded (hashed)
for security.

Q84. What is the ValidationSummary control in ASP.NET used for?
Ans. The ValidationSummary control in ASP.NET displays summary of all the
current validation errors.

Q85. What is AutoPostBack feature in ASP.NET?
Ans. In case it is required for a server side control to postback when any of its
event is triggered, then the AutoPostBack property of this control is set to true.

Q86. What is the difference between Web.config and Machine.Config in
.NET?
Ans. Web.config file is used to make the settings to a web application, whereas
Machine.config file is used to make settings to all ASP.NET applications on a
server(the server machine).

Q87. What is the difference between a session object and an application
object?
Ans. A session object can persist information between HTTP requests for a
particular user, whereas an application object can be used globally for all the users.



Q88. Which control has a faster performance, Repeater or Datalist?
Ans. Repeater.

Q89. Which control has a faster performance, Datagrid or Datalist?
Ans. Datalist.

Q90. How to we add customized columns in a Gridview in ASP.NET?
Ans. Make use of the TemplateField column.

Q91. Is it possible to stop the clientside validation of an entire page?
Ans. Set Page.Validate = false;

Q92. Is it possible to disable client side script in validators?
Ans. Yes. simplyEnableClientScript = false.

Q93. How do we enable tracing in .NET applications?
Ans. <%@ Page Trace="true" %>

Q94. How to kill a user session in ASP.NET?
Ans. Use the Session.abandon() method.

Q95. Is it possible to perform forms authentication with cookies disabled on a
browser?
Ans. Yes, it is possible.

Q96. What are the steps to use a checkbox in a gridview?
Ans. <ItemTemplate>
<asp:CheckBox id="CheckBox1" runat="server" AutoPostBack="True"
OnCheckedChanged="Check_Clicked"></asp:CheckBox>
</ItemTemplate>

Q97. What are design patterns in .NET?
Ans. A Design pattern is a repeatitive solution to a repeatitive problem in the
design of a software architecture.



Q98. What is difference between dataset and datareader in ADO.NET?
Ans. A DataReader provides a forward-only and read-only access to data, while
the DataSet object can carry more than one table and at the same time hold the
relationships between the tables. Also note that a DataReader is used in a
connected architecture whereas a Dataset is used in a disconnected architecture.

Q99. Can connection strings be stored in web.config?
Ans. Yes, in fact this is the best place to store the connection string information.

Q100. Whats the difference between web.config and app.config?
Ans. Web.config is used for web based asp.net applications whereas app.config is
used for windows based applications.


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