Frequently asked dot net questions

1.      Does C# support multiple-inheritance?
No.
 

2.      Who is a protected class-level variable available to?
It is available to any sub-class (a class inheriting this class).
 

3.      Are private class-level variables inherited?
Yes, but they are not accessible.  Although they are not visible or accessible via the class interface, they are inherited.
 

4.      Describe the accessibility modifier “protected internal”.
It is available to classes that are within the same assembly and derived from the specified base class.
 

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

6.      What does the term immutable mean?
The data value may not be changed.  Note: The variable value may be changed, but the original immutable data value was discarded and a new data value was created in memory.
 

7.      What’s the difference between System.String and System.Text.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.
 

8.      What’s the advantage of using System.Text.StringBuilder over System.String?
StringBuilder is more efficient in cases where there is a large amount of string manipulation.  Strings are immutable, so each time a string is changed, a new instance in memory is created.
 

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

10.  What’s the difference between the System.Array.CopyTo() and System.Array.Clone()?
The Clone() method returns a new array (a shallow copy) object containing all the elements in the original array.  The CopyTo() method copies the elements into another existing array.  Both perform a shallow copy.  A shallow copy means the contents (each array element) contains references to the same object as the elements in the original array.  A deep copy (which neither of these methods performs) would create a new instance of each element's object, resulting in a different, yet identacle object.

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

12.  What’s the .NET collection class that allows an element to be accessed using a unique key?
HashTable. 

13.  What class is underneath the SortedList class?
A sorted HashTable. 

14.  Will the finally block get executed if an exception has not occurred?­
Yes.

15.  What’s the C# syntax to catch 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 {}. 

16.  Can multiple catch blocks be executed for a single try statement?
No.  Once the proper catch block processed, control is transferred to the finally block (if there are any). 

17.  Explain the three services model commonly know as a three-tier application.
Presentation (UI), Business (logic and underlying code) and Data (from storage or other sources). 

18.  What is the syntax to inherit from a class in C#?
Place a colon and then the name of the base class.
Example: class MyNewClass : MyBaseClass 

19.  Can you prevent your class from being inherited by another class?
Yes.  The keyword “sealed” will prevent the class from being inherited.
 

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

21.  What’s an abstract class?
A class that cannot be instantiated.  An abstract class is a class that must be inherited and have the methods overridden.  An abstract class is essentially a blueprint for a class without any implementation.
 

22.  When do you absolutely have to declare a class as abstract?
1. When the class itself is inherited from an abstract class, but not all base abstract methods have been overridden.
2.  When at least one of the methods in the class is abstract. 

23.  What is an interface class?
Interfaces, like classes, define a set of properties, methods, and events. But unlike classes, interfaces do not provide implementation. They are implemented by classes, and defined as separate entities from classes.
 

24.  Why can’t you specify the accessibility modifier for methods inside the interface?
They all must be public, and are therefore public by default.
 

25.  Can you inherit multiple interfaces?
Yes.  .NET does support multiple interfaces.
 

26.  What happens if you inherit multiple interfaces and 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.
To Do: Investigate
 

27.  What’s the difference between an interface and abstract class?
In an interface class, all methods are abstract - there is no implementation.  In an abstract class some methods can be concrete.  In an interface class, no accessibility modifiers are allowed.  An abstract class may have accessibility modifiers. 

28.  What is the difference between a Struct and a Class?
Structsstructs cannot inherit. 

29.  What’s the implicit name of the parameter that gets passed into the set method/property of a class?
Value.  The data type of the value parameter is defined by whatever data type the property is declared as.
 

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

31.  How is method overriding different from method overloading?
When overriding a method, you change the behavior of the method for the derived class.  Overloading a method simply involves having another method with the same name within the class.
 

32.  Can you declare an override method to be static if the original method is not static?
No.  The signature of the virtual method must remain the same.  (Note: Only the keyword virtual is changed to keyword override)
 

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

34.  If a base class has a number of overloaded constructors, and an inheriting class has a number of overloaded constructors; can you enforce a call from an inherited constructor to a specific 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.

35.  What’s a delegate?
A delegate object encapsulates a reference to a method.
 

36.  What’s a multicast delegate?
A delegate that has multiple handlers assigned to it.  Each assigned handler (method) is called.

37.  Is XML case-sensitive?
Yes.
 

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

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

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

41.  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.
 

42.  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.
 

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

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

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

46.  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).
 

47.  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. 

48.  What is the role of the DataReader class in ADO.NET connections?
It returns a read-only, forward-only rowset from the data source.  A DataReader provides fast access when a forward-only sequential read is needed.
 

49.  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.  OLE-DB.NET is a .NET layer on top of the OLE layer, so it’s not as fastest and efficient as SqlServer.NET.
 

50.  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%’.
 

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

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

53.  Between Windows Authentication and SQL Server Authentication, 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.
 

54.  What does the Initial Catalog parameter define in the connection string?
The database name to connect to.
  

55.  What does the Dispose method do with the connection object?
Deletes it from the memory.
To Do: answer better.  The current answer is not entirely correct.
 

56.  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.  The connection string must be identical

57.  How is 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.
 

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

59.  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.
 

60.  What namespaces are necessary to create a localized application?
System.Globalization and System.Resources.
 

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

62.  When should you call the garbage collector in .NET?
As a good rule, you should not call the garbage collector.  However, you could call the garbage collector when you are done using a large object (or set of objects) to force the garbage collector to dispose of those very large objects from memory.  However, this is usually not a good practice.
 

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

64.  What happens in memory when you Box and Unbox a value-type?
Boxing converts a value-type to a reference-type, thus storing the object on the heap.  Unboxing converts a reference-type to a value-type, thus storing the value on the stack

Sungard Dot Net Interview Questions and Answers

1) Diff between UI thread and background thread?

Ans: By default, threads you create explicitly are foreground threads.

Foreground threads keep the application alive for as long as any one of them is running,

whereas background threads do not. Once all foreground threads finish, the application ends,

and any background threads still running abruptly terminate.

You can query or change a thread’s background status using its IsBackground property.

2) Diff bet del and event? how del is different from event?

Ans: Event is a reference of delegate i.e. when event will be raised delegate will be called.

The object that raises the event is called the event sender.

The object that captures the event and responds to it is called the event receiver.

3) What is Accessors and Modifier?

4) Explain the difference between composition and aggregation?
Ans:An Association is a channel between classes through which messages can be sent.
Suppose you have a class named UserInformation . And with that class you are having a object instance named UserContactInfo

Class UserInformation {

UserContactInfo userContactInfo ;

}

This leads to aggregation. The UserContactInfo object is aggreated within UserInformation class. Both the classes have individual identity.

Now suppose we have a class named Rectangle . And within that class you have Class Point as a object.

Class Rectangle {

Point point ;

}

Now rectangle is a composition of points. Point class doesn't have any individual important .
It is point that makes a rectangle . This is known as composition.

5) What is dangling pointer?
Ans: 
The pointer is referring the location which does not exist. 

6) What is static variable and class?
Ans:
The variable which has common memory area and shares between accessible area

7) Advantages of views over physical tables?
Ans:Advantages
a). You can use triggers with views
b). Views can be updatable
c). You can create indexes on views
d). Optimizations for partitioned views
e). hiding the data.
f). you can use two tables data in view.
g). security will be there.

disadvantages
a). when table is not there view will not work.
b). dml is not possible if that is more than one table with non normalized.
c). it is also database object so it will occupy the space.
d). view is it affects performance. Querying from view takes more time than directly querying from the table

8) What is cursors and its uses?
Ans:
A cursor is a set of rows together with a pointer that identifies a current row.

In other word, Cursor is a database object used by applications to manipulate data in a set on a row-by-row basis,
its like recordset in the ASP and visual basic.  


CREATE PROCEDURE sp_Test()
as

DECLARE @colA nvarchar(10)
DECLARE @colB nvarchar(10)
DECLARE @MyCursor CURSOR

SET @MyCursor = CURSOR FAST_FORWARD
FOR
Select colA,colB
From tableA

OPEN @MyCursor
FETCH NEXT FROM @MyCursor
INTO @ColA,@ColB

WHILE @@FETCH_STATUS = 0
BEGIN
PRINT @ColA
PRINT @ColB
FETCH NEXT FROM @MyCursor
INTO @ColA,@ColB
END

CLOSE @MyCursor
DEALLOCATE @MyCursor
GO

9) Difference between Output parameter and Return Value in SP?
Ans:
Return will exit stored proc and argument supplied to return will be the status of return.

xxxx
return 1
yyyy

If above part is inside body of stored proc, then yyyy wont execute after return. Stored proc will exit with exit status 1.

10) How to set output parameter through programming?

Ans:

SQLConnection conn = new SQLConnection("Conn");

conn.open();

Sqlcommand comm=new Sqlcommand("sp_Emp",conn);

comm.commandType=commandType.StoredProcedure;

comm.parameters.add("@Name",SqlDbType.Varchar(50).value=txtName.text;

comm.parameters.add("@Phone",SqlDbType.Varchar(50).value=txtPhone.text;

comm.Parameters.add("@Id",SqlDbType.int);

comm.parameters["@Id"].Direction=parameterdirection.output;

comm.ExecuteNonQuery();

conn.close();

11) How to load assembly dynamically?

12) What is @@ERROR?

13) How do we pass default value as input parameter in a store procedure?

Ans:

CREATE or REPLACE PROCEDURE proc_test

(name IN varchar2 DEFAULT 'Me' )

AS

BEGIN

dbms_output.put_line('My name is proc_test ' || name);

END;

SQL> exec proc_test('hello');

My name is proc_test hello

SQL> exec proc_test();

My name is proc_test Me

14) What is collection?

15) What is generics?

16) How to add two different dll's with same name with same version in GAC?

17) One Dll is added in GAC with two versions lets say 1.0.0.0 and 1.0.0.1 and both versions contain same function

name but it has different functionality then how to call both version functions?

18) Difference between stored procedure and functions?
Ans:
1>Procedure can return zero or n values whereas function can return one value which is mandatory.

2>Procedures can have input,output parameters for it whereas functions can have only input parameters.

3>Procedure allow select as well as DML statement in it whereas function allow only select statement in it.

4>Functions can be called from procedure whereas procedures cannot be called from function.

5>Exception can be handled by try-catch block in a procedure whereas try-catch block cannot be used in a function.

6>We can go for transaction management in procedure whereas we can't go in function.

7>Procedures can not be utilized in a select statement whereas function can be embedded in a select statement.

8> Functions are compiled and executed at run time.
Stored procedures are stored in parsed and compiled format in the database.

9> Functions cannot affect the state of the database which means we cannot perform insert,delete,update and create operations on the database.
Stored Procedures can affect the state of the database by using insert,delete,update and create operations.

10> Functions are basically used to compute values. We passes some parameters to functions as input and then it performs some operations on the parameter and return output.
Stored procedures are basically used to process the task.

19) Difference between data abstraction and data encapsulation?

20) How to call abstract method without creating instance?

Ans: Add Static method in it.

21) difference between abstract class and interface class?

22) Difference between truncate and delete commands?

23) Design table structure for many to many relationship table? e.g. author and books many to many relation tables?

24) What are clustered and non clustered index?

25) Which index is faster and preferred in case of insert and update statement?

26) What is triggers?

27) how to pass values to the trigger?

28) Is there any collection type in trigger?

29) Types of trigger?

30)

    EmpID   Salary

    1    1000

    2    2000

    3    3000

    4    4000

    5    5000

    6    6000

    7    7000

Write a query, Give the increment 5000 for those who having salary < 4999 and Give the increment 3000 for those who having salary > 4999

Ans: use case statement in case of T-SQL statment.

31) How you can pass or send data from one table to another table?

32) How to release memory for COM objects?
Ans: Marshal.ReleaseComObject(ObjctName)

33) How to use com in .net? What is RCW?

34) How to use .net object in com ? What is RCW?

25) Interface for implement cleaning memory?

26) What is finalizesupress?

27) What is web service? and what is purpose of it?

28) What is SOAP protocol?

29) What happen when you do add reference for web service and normal dll?

30) What is multi threading and multi tasking?

31) What is concurrency?

32) what is asynchronous?

33) What is asynchronous patterns?

34) What is delegate?

35) What is event?

36) How events are assciated with delegates?

37) How XML is platform independent?

38) What is SQL Injection?

39) Deterministic and non deterministic Algorithm of GC?

40) Generalization and Specialization?

Ans: Generalization is abstract class and Specialization is inheritance.

41) In Web Service, if hosted server is changed to another then tell the mechanism client code should work without changing or compiling client code? how things need to do in client application?
Ans: a) While adding reference please add hostname instead of IP address.
             e.g. Http://127.127.1.1/MyService.aspx (This is a wrong) change it to Http://MyMachine/MyService.aspx (Correct)
        b) After adding web service select web service reference and go to the property and change URL Behaviour property from Static to Dynamic. Bydefault it is static. Changing to Dynamic it will add code in app.config (if app.config file is not present then please add it, bydefault it should get created). so whenever URL changes it takes at run time.

42) What is postback event/del? and how to implement? and where it uses?

43) diff between user control and custom control?

ans:

1.User Control is a page file with extension .ascx which can only be used within
a single application. But custom controls are assemblies(dll files) that can be
used in multiple applications.

2.User Controls cannot be added to the ToolBox of VS.NET . To use a user Control with in an
aspx page u have to drag the user Control from the solution Explorer to designer page.
But Custom Controls can be added to ToolBox of VS.NET.

44) Asych Web Service?
Ans: serviceobj.BeginMethodName("WebService Parameter if any", new AsyncCallback(MethodName), null);

public void MethodName(IAsyncResult ar)
{
    string str = serviceobj.endMethodName(ar);
} 

45) How to overload method in web service?
Ans: use 'MessageName' attribute with WebMethod and also Change WebserviceBinding value to Profiles None.

46) What is Silverlight?
Ans: used to develope rich UI and provided by microsoft.

47) How to maintain session in Webservice?
ans: using EnableSession = true property. By Default this property is false. 


48) Difference between hashtable and Dictionary?
Ans: Hash table is non generic, stores value in key and value pair as a object and implements ICollection and IDictionary interfaces and boxing is required so performance is issue. Where as Dictionary is generic,  stores value in key and value pair as a type and type verification is done at compile time so it is faster than other hashtable and boxing is not required.  

49) How to synchronize method?
Ans: using  [System.Runtime.CompilerServices.MethodImpl(System.Runtime.CompilerServices.MethodImplOptions.Synchronized)] attribute.
Just add above attribute to any method which developer wants to synchronize. 
  
50) In partial class, two functions with same signature can be added?
Ans:No

51) Is partial function available?
Ans:Yes, but one should be declaration and another should be definition.


52) What is the disco file and where it is located?
Ans:It is used to discover the webservice location. it is located on client web service reference folder. 

53) Can you write return statement in finally block?
Ans:No, compile time error will occurred.

54) What is difference between when passing object as parameter and passing by ref?
Ans:In normal case if object is newly created using new keyword in method then new data will not be hold in object after existing method but in case of by ref new data will be hold.


55) How to pass event from master web page to normal container page?
Ans:

56) how to call server side function or call web service through java script?
Ans:

57) securities in web service?
Ans:

58) In ASP.net page life cycle where new control can be created?
Ans:

59) Can viewState destroy in page life cycle?
Ans:

60) What is default timout for web service?
Ans: 100 Sec.