.NET Interview Questions

Serialization in .NET?

noreply@blogger.com (Ajay) — Tue, 30 Aug 2011 14:37:00 +0000

Serialization is the process of converting an object into a form so that it can be persisted int the storage location(memory,a database or a file) or can be transported across the network.Main purpose of Serialization is to save the state of an object in order to be able to recreate it when needed. The reverse process is called deserialization.The object is serialized to a stream, which carries not just the data, but information about the object's type, such as its version, culture, and assembly name. From that stream, it can be stored in a database, a file, or memory.

Serailization usage:
Serialization allows the developer to save the state of an object and recreate it as needed, providing storage of objects as well as data exchange.By using Serailizaton,we can send the object to a remote application by means of web service,passing an object from one domain to another be means of .net remoting,passing an object through firewall as an XML string or passing the user specific information across applications.

How do you use serailizataion:
Serialization is handled by classes and interfaces in the System.Runtime.Serialization namespace.you need to do two things to serialize an object.
1)a stream to contain the serialized objects
2)a formatter to serialize the objectds into the stream.

.NET serialization formats:
There are three fromats of serialization.
1) Binary Serialization : Light and compact used in Remoting
2) SOAP Serialization : Interoperable use SOAP and used in web Services
3) XML Serialization    : Custom Serialization

SOAP and Binary Serialization:
Serialization is always needed when you transfer an object across a network.Both XML and Binary Serialization can serialize the entire object and all those object that are being refrenced by it.This is why it is also called Deep Serialization.SOAP sends it using HTTP Protocol which makes it most interoperable while Binary serialization is known for its light and compact nature. Web Services uses the SOAP Serialization and Remoting uses the Binary Serialization.If you want any class to serialize through any of these methods you should mark the class as [Serializable].

XML Serilization:
XML Serilization serialize only the public members.For XML Serialization,you need to use [Serializable] attribute and specify them for every public member which you to serialize.This is why it is also called Shallow Serialization.

Note : The [NonSerialized] Attribute can be used to keep specific fields from being serialized.

Serialize an object with Binary Format (Binary Serialization Example) :
I am trying to give an example of Binary Serialization,which converts an employee object into stream(i saved it in a text file) and recreating the object by using stream which is saved in text file.
Example:
using System;
using System.Collections.Generic;
using System.Text;
using System.Runtime.Serialization;
using System.Runtime.Serialization.Formatters.Binary;
using System.IO;

namespace Serialization
{
    class Program
    {
        static void Main(string[] args)
        {

            Employee emp = new Employee();
            string filename = @"C:\Serialization.txt";
            WriteToFile(emp,filename);
            ObjectFromFile(filename);
            Console.ReadLine();
        }

        public static void WriteToFile(Employee emp, String filename)
        {
            Stream stream = File.OpenWrite(filename);
            BinaryFormatter formatter = new BinaryFormatter();
            formatter.Serialize(stream, emp);
            stream.Close();
        }

        public static void ObjectFromFile(String filename)
        {
            Stream stream = File.OpenRead(filename);
            BinaryFormatter formatter = new BinaryFormatter();
            stream.Position = 0;
            object o = formatter.Deserialize(stream);
            stream.Close();
            Employee emp = (Employee)o;
            Console.WriteLine(emp.Empid + " " + emp.EmpName);
        }
    }

    [Serializable]
    class Employee
    {
        private int empid;
        private string empName;

        public int Empid
        {
            get
            {
                return empid;
            }
            set
            {
                this.empid = value;
            }
        }
        public string EmpName
        {
            get
            {
                return empName;
            }
            set
            {
                this.empName = value;
            }
        }

        public Employee()
        {
            empid = 1;
            empName = "Johny";
        }
    }
}

output in console:
1 Johny

I hope you can better understand what is a serialization in .NET and How to serialize an object and reconstruct the object by using Binary,SOAP serialization.

Method Overriding and Method Hiding [C#]

noreply@blogger.com (Ajay) — Tue, 30 Aug 2011 14:35:00 +0000

Method Overriding vs Method Hiding

Method Hiding is the concept of hiding the base class function from the derived class.We can create the complete new definition of base class function in derived class function.we can say hiding the base class function from derived class.Method Hiding can be achieved by using new keyword.

public class Base
{
public void Hello()
{
                   Console.WriteLine("Base Class");
}
}
        public class Derived : Base
        {
         public new void Hello()
               {
                   Console.WriteLine("Derived Class");
               }
         }
         public class TestHiding
         {
             public static void Main(string[] args)
             {
      Derived  obj= new Derived ();

obj.Hello();
                  Console.ReadLine();
            }

}

Output : Derived Class

Method overriding means having two methods with same name and same siganture, one method in base class and other method in derived class.
   A subclass inherits methods from a base class. Sometimes, it is necessary for the subclass to modify the methods defined in the base class. This is referred to as method overriding.
   This can be achieved by using the virtual and override keywords. we have to use the virtual keyword for the method which in base class and override keyword for the method in subclass.

   By default functions are not virtual in C# and so you need to write “virtual” explicitly.

   Class BaseClass
{
public virtual void hello()
    { Console.WriteLine(“Base Class”); }
}

Class SubClass : BaseClass
{
public override void hello()
   { Console.WriteLine(“SubClass”); }
}

static void main()
{
    BaseClass objBase = new SubClass();
    objBase.hello();
}

//Output ::: SubClass....

sealed keyword for methods | sealed methods [C#]

noreply@blogger.com (Ajay) — Tue, 30 Aug 2011 14:33:00 +0000

Sealed methods,how to use sealed methods

Yes. .NET allows the sealed methods.Sealed methods are used to define the overriding level of the virtual methods.Sealed keyword is always used with the override keyword.

namespace sealedMethod_Example
{
    class Program
    {
        public class Base
        {
            public virtual void Test()
            {
                Console.WriteLine("Base Method");
            }
        }

       public class Derived : Base
        {

           // Now the Test() has been sealed and can't be overridden
            public override sealed void Test()
            {
                Console.WriteLine("Derived Class Sealed method");
            }
        }
       //public class ThirdClass : Derived
       //{
       //    public override void Test()
       //    {
                 //Here we are trying to override the Test(),but it's not possible becasue we have been sealed Test() in Derived Class So it will give error.
       //    }
       //}

        static void Main(string[] args)
        {
            Derived d = new Derived();
            d.Display();
         }
       }
   }

sealed classes,sealed methods in C#

noreply@blogger.com (Ajay) — Tue, 30 Aug 2011 14:32:00 +0000

Sealed class is like the normal class but the sealed class can't inherited but can be instantiated like normal class.To declare sealed class we should use the sealed keyword with the class declaration.The sealed classes are useful inorder to protect our classes not to be used by any other classes.

Syntax :

   sealed class Employee
   {
       protected string ename;
   }

out and ref parameters for void method [C#]

noreply@blogger.com (Ajay) — Tue, 30 Aug 2011 14:29:00 +0000

Yes we can use the out parameter for method type of void.it won't give any compilation errors.Because it out and ref parameters doesn't depend on return type of the method.

Return multiple values from the function

noreply@blogger.com (Ajay) — Tue, 30 Aug 2011 09:22:00 +0000

We can return multiple values from the function by using out parameters.

    The out parameters are used to return values in the same variables, that you pass an an argument of a method.out parameters are very useful when your method needs to return more than one values.

    Example:

    using System;
    class SomeName
    {
        public static void Main(String [] args)
        {
           int a,b=0;
           b=ParamTest(out a);
           Console.WriteLine("a = {0}", a);
           Console.WriteLine("b = {0}", b);
         }
        public static int ParamTest(out int a)
        {
            a=200;
            return 10;
        }
    }

   output : a=200 b=10;

Return the identity value for an inserted row in SQL SERVER

noreply@blogger.com (Ajay) — Thu, 18 Aug 2011 13:16:00 +0000

We have several statements for returning the identity value for an inserted row.

1)scope_identity()
2)ident_current
3)@@identity

1) scope_identity() will return the last identity inserted in the current scope and session.
2)ident_current('Table Name') returns the last value inserted into that table on any connection. Remember to put the table name in quotes
3)@@identity will return the last identity value inserted in any scope.

Different types of transaction in SQL SERVER

noreply@blogger.com (Ajay) — Thu, 18 Aug 2011 13:15:00 +0000

There are three types of transactions.
    1)Auto commit transaction
    2)Implicit transaction
    3)Explicit transaction

1)Auto commit transaction : This is the default transaction mode in sql server.Every SQL statement in sql server is either committed or rolled back. If it completes successfully it is committed else it is rolled back.
2)Implicit transaction : A new transaction is starts automatically when the current transaction is committed or rolled back.No need to define the start of the transaction. It generates continues chain of transactions.
3)Explicit transaction : ransactions that have a START and END explicitly written are called as an explicit transaction. They last only for the duration of the transaction.

@@ERROR variable in SQL SERVER 2005

noreply@blogger.com (Ajay) — Thu, 18 Aug 2011 13:14:00 +0000

The @@ERROR automatic variable is used to implement error handling code. @@ERROR variable contains the error ID which is produced by the last SQL statement executed during a client's connection. When a statement executes successfully, @@ERROR set to 0.

Transactions in SQL SERVER 2005

noreply@blogger.com (Ajay) — Thu, 18 Aug 2011 13:14:00 +0000

Transactions are a gruop of tasks into a single execution unit. Each transaction begins with a specific task and ends when all the tasks in the group successfully complete.So Transaction has only two results : success or failure.If all the tasks in a group are successful then the transaction is success.If any of the task in a group fails then the transaction fails.
    Users can group two or more SQL statements into a single transaction using the following statements:
    Begin Transaction
    Rollback Transaction
    Commit Transaction

    Syntax:

    BEGIN TRAN
    UPDATE Employee SET emp_firstname = 'John' WHERE emp_id = 1
    IF @@ERROR <> 0
    BEGIN
         ROLLBACK TRAN
         return 11
   END
   COMMIT TRAN

   If the statement failed (i.e. @@ERROR <> 0) then we rollback the work performed so far and use the RETURN statement to exit the stored procedure.

How can we view all the triggers in a table

noreply@blogger.com (Ajay) — Thu, 18 Aug 2011 13:13:00 +0000

By Using sp_helptrigger sytax we can view all the triggers in a table.
sp_helptrigger Table_Name,it will list all the triggers present in a table

Is it possible to disable perticular trigger on a table?

noreply@blogger.com (Ajay) — Thu, 18 Aug 2011 13:13:00 +0000

Yes,we can disable particular trigger on a table.
ALTER TABLE Table_Name DISABLE TRIGGER trgAfter /*trgAfter is a trigger name*/

Can we disable all the triggers on particular table

noreply@blogger.com (Ajay) — Thu, 18 Aug 2011 13:12:00 +0000

Yes, we can disabled/enabled all the triggers for a specific table.
ALTER TABLE Table_Name [ENABLE|DISBALE] TRIGGER ALL

Instead Of Triggers in SQL SERVER 2005 and it's Syntax

noreply@blogger.com (Ajay) — Thu, 18 Aug 2011 13:11:00 +0000

Instead of trigger executes the code inside of the trigger instead of an Insert/delete/update commands.But we can write a code to insert/delete/update row inside the trigger.
    Instead of Triggers can be classified into 3 types.
    1.INSTEAD Of INSERT Trigger
    2.INSTEAD Of UPDATE Trigger
    3.INSTEAD Of DELETE Trigger

    Syntax:
    CREATE TRIGGER trgInsteadOf ON [dbo].[Table_Name]
    INSTEAD OF DELETE /*Here we can use UPDATE or DELETE also for INSTEAD OF UPDATE and INSTEAD OF DELETE Triggers*/
    AS
    -- write sole logic
    PRINT 'Instead Of Trigger fired.'
    GO

After Triggers in SQL SERVER 2005 and After Trigger Syntax

noreply@blogger.com (Ajay) — Thu, 18 Aug 2011 13:10:00 +0000

After Triggers run after an insert, delete and update.Views are not supported After Triggers.
    After Triggers can be classified into 3 types.
    1.AFTER INSERT Trigger
    2.AFTER UPDATE Trigger
    3.AFTER DELETE Trigger

    Syntax : AFTER INSERT Trigger
    CREATE TRIGGER trgAfter ON [dbo].[Table_Name]
    FOR INSERT /*Here we can use UPDATE or DELETE also for AFTER UPDATE and AFTER DELETE Triggers*/
    AS
                 -- write some logic
    PRINT 'AFTER Trigger fired.'
    GO

Triggers in SQL SERVER and Types of Trigges in SQL SERVER

noreply@blogger.com (Ajay) — Thu, 18 Aug 2011 13:09:00 +0000

Triggers are special types of Stored Procedures that are defined to execute automatically in place of or after data modifications. They can be executed automatically on the INSERT, DELETE and UPDATE commands on a table.we can't explicitly execute triggers.
    There are two types of triggers
    1)After Trigger
    2)Instead of Trigger

refer types of triggers in detail
After Triggers in SQL SERVER 2005 and After Trigger Syntax
Instead Of Triggers in SQL SERVER 2005 and it's Syntax

Difference between function and stored porcedure in SQL SERVER

noreply@blogger.com (Ajay) — Thu, 18 Aug 2011 13:08:00 +0000

The main differences between functions and stored procedures are
    1)Functions can be used in SQL Queries where as stored procedures can't be used in SQL queries.
    2)Stored procedure can run independently. It can be executed using EXECUTE or EXEC command where as function cannot run independently.
    3)stored procedures has both in and out parameters,but the function takes only in parameters.
    4)A FUNCTION is always returns a value using the return statement. A PROCEDURE may return one or more values through parameters or may not return at all
    5)Functions are normally used for computations where as procedures are normally used for executing business logic.
    6)Stored procedure is precompiled execution plan where as functions are not.

Advantage of stored procedure over query in SQL SERVER 2005

noreply@blogger.com (Ajay) — Thu, 18 Aug 2011 13:07:00 +0000

Stored procedure are precompiled and executed directly and it may contian block of SQL statements.
When client sends to request to execute query,every time it will compile first and executes the query.

Stored procedure in SQL SERVER and Advantage of using stored procedure in SQL SERVER

noreply@blogger.com (Ajay) — Thu, 18 Aug 2011 13:07:00 +0000

Stored procedure is a database object which contains one or more T-SQL statements that are stored in database.To use the stored procedure you send a request for it to be executed. When server recieves the request, it executes the stored procedure.
Adavantages:
    Stored procedures improve the database performance because stored procedures are pre-compiled and executes directly when client sends the request to execute the procedure.

   Syntax:

   CREATE PROCEDURE spVendorByState
          @VendorState varchar(50)
   AS
   BEGIN
          SELECT * FROM Table
    END
    GO

Difference between UNION and UNION ALL Commands

noreply@blogger.com (Ajay) — Thu, 18 Aug 2011 13:05:00 +0000

UNION : UNION Command is used to select the related information from two tables.When using the UNION command , the selected columns need to be of same datataype.with UNION Command only the distinct values are selected.
UNION ALL : UNION ALL Command is equal to the UNION Command except the UNION ALL select all the values.

    ex:

    Table1

         id    rank
         1    First
         2    Second
         3    Third
         4    Fourth

    Table2

         id    rank
         1    First
         2    Second
         3    Seventh
         4    Tenth

     UNION:
     select rank from Table1 UNION select rank from table2

      result:

          First
          Second
          Third
          Fourth
          Seventh
Tenth

     UNION ALL:
     select rank from Table1 UNION ALL select rank from table2

     result:

             First
             Second
             Third
             Fourth
             First
             Second
             Seventh
             Tenth

SELF JOIN Example and scenario in SQL SERVER 2005

noreply@blogger.com (Ajay) — Thu, 18 Aug 2011 12:39:00 +0000

A self-join is a query in which a table is joined to itself.Self-joins are used to compare values in a column with other values in the same column in the same table.
    ex:
----------------------------------------------------
    empID    Name         ManagerID
----------------------------------------------------
       1   John         NULL
       2           Steve          1
       3           Billgates     1
       4          Ozzy            2
       5          Homer         3
-----------------------------------------------------

       if we want to display all the employees with their Managers names.In this scenario we can use self-join

CROSS JOIN Example in SQL SERVER 2005

noreply@blogger.com (Ajay) — Thu, 18 Aug 2011 12:36:00 +0000

CROSS-JOIN is a Cartesian join that does not necessitate any condition to join.The resultset contains records that are multiplication of record number from both the tables.suppose if we have 10 records in table A and 5 records in table B,it will return 50(10*5) records.

     Ex:
     Left Table(emp Table)

         --------------------------------
    empID    FirstName
         --------------------------------
       1    John
       2    Steve
        ---------------------------------

     Right Table(dept Table)

         ------------------------------------------------------
    empID        DeptName
         ------------------------------------------------------
    1        IT
    2        Networking
         ------------------------------------------------------

     Query:
         SELECT * FROM emp AS e FULL JOIN dept AS d

     Result:

           empID     FirstName        IndividualId    AccessLevel
            1              John                             1           IT
            1      John                             2           Networking
            2      Steve                           1           IT
            2              Steve                           2           Networking

FULL OUTER JOIN Example in SQL SERVER 2005

noreply@blogger.com (Ajay) — Thu, 18 Aug 2011 12:31:00 +0000

A FULL OUTER JOIN Join combines Left outer join and right outer join.it will display the rows from either tables when the condtions are met and returns null when there is no match found.

     Ex:
     Left Table(emp Table)

------------------------------------------------------------------------
    empID    FirstName    LastName    UserName
   ------------------------------------------------------------------------
       1             John          Miller                 John
       2   Steve         Jobs                    Steve
       3           Billgates     john                    Billgates
       4           Ozzy         Ozzbourne   Ozzy
       5           Homer         Gain                   Homer
        --------------------------------------------------------------------------

     Right Table(dept Table)

------------------------------------------------------
    empID        DeptName
------------------------------------------------------
    1        IT
    2        Networking
    3        Networking
    4        Networking
    12        Admin
------------------------------------------------------

     Query :

     SELECT * FROM emp AS e
     FULL JOIN dept AS d
     ON e.empid = d.empid

    result:

    empID     FirstName    LastName        UserName    IndividualId    AccessLevel
        1               John             Miller              John                 1       IT
        2               Steve         Jobs                 Steve                2              Networking
        3            Billgates         john                 Billgates          3              Networking
        4             Ozzy             Ozzbourne       Ozzy                4              Networking
        5            Homer            Gain                Homer        NULL           NULL
    NULL       NULL             NULL               NULL           12       Admin

RIGHT OUTER JOIN Example in SQL SERVER

noreply@blogger.com (Ajay) — Thu, 18 Aug 2011 12:30:00 +0000

This join returns all the rows from the right table with the matching rows from the left table. If there are no columns mathcing in the left table ,it returns NULL values.
    Use Right Outer Join when you only want to return rows that have matching data in the right table, even if there's no matching rows in the left table.

Ex:

     Left Table(emp Table)

    ------------------------------------------------------------------------
    empID    FirstName    LastName    UserName
    ------------------------------------------------------------------------
       1               John         Miller        John
       2   Steve         Jobs        Steve
       3      Billgates         john        Billgates
       4            Ozzy         Ozzbourne    Ozzy
       5            Homer         Gain             Homer
   --------------------------------------------------------------------------

     Right Table(dept Table)

------------------------------------------------------
    empID        DeptName
------------------------------------------------------
    1        IT
    2        Networking
    3        Networking
    4        Networking
    12        Admin
   ------------------------------------------------------

     Query :

     SELECT * FROM emp AS e
     RIGHT JOIN dept AS d
     ON e.empid = d.empid

    result:

    empID     FirstName    LastName        UserName    IndividualId    AccessLevel
        1            John             Miller                 John                1                      IT
        2            Steve             Jobs                  Steve       2        Networking
        3          Billgates         john                Billgates            3        Networking
        4   Ozzy             Ozzbourne           Ozzy       4        Networking
   NULL       NULL        NULL                    NULL         12        Admin

LEFT OUTER JOIN Example in SQL SERVER 2005

noreply@blogger.com (Ajay) — Thu, 18 Aug 2011 12:26:00 +0000

This join returns all the rows from the left table with the matching rows from the right table. If there are no columns matching in the right table, it returns NULL values.

Use this when you only want to return rows that have matching data in the left table, even if there's no matching rows in the right table.
     Ex:

     Left Table(emp Table)

         ------------------------------------------------------------------------
   empID    FirstName    LastName    UserName
         ------------------------------------------------------------------------
    1             John         Miller             John
              2   Steve        Jobs              Steve
              3          Billgates    john              Billgates
              4             Ozzy         Ozzbourne    Ozzy
              5            Homer        Gain             Homer
        --------------------------------------------------------------------------

     Right Table(dept Table)

         ------------------------------------------------------
            empID        DeptName
         ------------------------------------------------------
   1          IT
               2          Networking
               3          Networking
   4          Networking
              12          Admin
         ------------------------------------------------------

     Query:

     SELECT * FROM emp AS e
     LEFT JOIN dept AS d
     ON e.empid = d.empid

    result:

    empID     FirstName    LastName        UserName    IndividualId    AccessLevel
        1             John             Miller                 John                 1                     IT
        2             Steve         Jobs                    Steve                2             Networking
        3             Billgates    john                    Billgates          3             Networking
        4             Ozzy         Ozzbourne          Ozzy                4             Networking
        5             Homer        Gain                    Homer        NULL          NULL