ADO.Net Interview Question and Answers

ADO.Net Interview Question and Answers

1. What is Ado.NET?

   ADO.NET is an object-oriented set of libraries that allows you to interact with data sources.     ADO.NET is a set of classes that expose data access services to the .NET programmer. ADO.NET is also a part of the .NET Framework.  ADO.NET is used to handle data access.

2. What are the two fundamental objects in ADO.NET?

    There are two fundamental objects in ADO.NET. Datareader - connected architecture and Dataset - disconnected architecture.

3.  What are the data access namespaces in .NET?

    The most common data access namespaces :

    System.Data    System.Data.OleDb   System.Data.SQLClient   System.Data.SQLTypes

   System.Data.XML

4. What are major difference between classic ADO and ADO.NET?

    In ADO the in-memory representation of data is the recordset.A Recordset object is used

to hold a set of records from a database table.In ADO.NET we have dataset.A DataSet is an in memory representation of data loaded from any data source.

5.  what is the use of connection object in ado.net?

   The ADO Connection Object is used to create an open connection to a data source.

Through this connection, you can access and manipulate a database.

6. What are the benefits of ADO.NET?

    Scalability    

    Data Source Independence

    Interoperability   

     Strongly Typed Fields

    Performance

7. What is a Clustered Index?

   The data rows are stored in order based on the clustered index key. Data stored is in a

sequence of the index. In a clustered index, the physical order of the rows in the table is the

same as the logical (indexed) order of the key values. A table can contain only one clustered

index. A clustered index usually provides faster access to data than does a non-clustered index.

8.  What is a Non-Clustered Index?

   The data rows are not stored in any particular order, and there is no particular order to the

sequence of the data pages. In a clustered index, the physical order of the rows in the table is

not same as the logical (indexed) order of the key values.

9. Whate are different types of Commands available with DataAdapter ?

    The SqlDataAdapter has

    SelectCommand    

    InsertCommand    

    DeleteCommand

    UpdateCommand

10. What is the difference between an ADO.NET Dataset and an ADO Recordset?

      Dataset can fetch source data from many tables at a time, for Recordset you can achieve the same only using the SQL joins. A DataSet can represent an entire relational database in memory, complete with tables, relations, and views, A Recordset can not.

 A DataSet is designed to work without any continues connection to the original data source;

Recordset maintains continues connection with the original data source. DataSets have no current record pointer, you can use For Each loops to move through the data. Recordsets have pointers to move through them.

11. Which method do you invoke on the DataAdapter control to load your generated dataset

with data?

    DataAdapter’ fill () method is used to fill load the data in dataset.

12. What are the different methods available under sqlcommand class to access the data?

      ExecuteReader - Used where one or more records are returned - SELECT Query.

      ExecuteNonQuery - Used where it affects a state of the table and no data is being  

queried -  INSERT, UPDATE, DELETE, CREATE and SET queries.

     ExecuteScalar - Used where it returns a single record.

13  .Explain the namespaces in which .NET has the data functionality class.

  System.data contains basic objects. These objects are used for accessing and storing  

relational data. Each of these is independent of the type of data source and the way we   

connect to it.

  These objects are:

  DataSet  

  DataTable

  DataRelation.

  System.Data.OleDB objects are used to connect to a data source via an OLE-DB provider.  These objects have the same properties, methods, and events as the SqlClient equivalents. A few of the object providers are:

 OleDbConnection

 OleDbCommand

 System.Data.SqlClient objects are used to connect to a data source via the Tabular Data 

Stream (TDS) interface of only Microsoft SQL Server. The intermediate layers required by an OLE-DB connection are removed in this. This provides better performance.

 System.XML contains the basic objects required to create, read, store, write, and manipulate 

XML documents according to W3C recommendations.

14.  Overview of ADO.NET architecture.

  Data Provider provides objects through which functionalities like opening and closing 

connection, retrieving and updating data can be availed. It also provides access to data source like SQL Server, Access, and Oracle). Some of the data provider objects are: Command object which is used to store procedures. Data Adapter which is a bridge between datastore and dataset. Datareader which reads data from data store in forward only mode.

 A dataset object is not in directly connected to any data store. It represents disconnected and 

cached data. The dataset communicates with Data adapter that fills up the dataset. Dataset 

can have one or more Datatable and relations.   DataView object is used to sort and filter data in Datatable. 

 ADO.NET provides access to all kind of data sources such as Microsoft SQL Server, OLEDB, 

Oracle, XML.

 ADO.NET separates out the data access and data manipulation componenets. ADO.NET 

includes some providers from the .NET Framework to connect to the database, to execute 

commands, and finally to retrieve results. Those results are either directly used or can be put 

in dataset and manipulate it.

14. Define connected and disconnected data access in ADO.NET

 Data reader is based on the connected architecture for data access. Does not allow data

manipulation

 Dataset supports disconnected data access architecture. This gives better performance results.Define connected and disconnected data access in ADO.NET Data reader is based on the connected architecture for data access. Does not allow data manipulation

Dataset supports disconnected data access architecture. This gives better performance results.

15.Describe CommandType property of a SQLCommand in ADO.NET.

CommandType is a property of Command object which can be set to Text, Storedprocedure.

If it is Text, the command executes the database query. When it is StoredProcedure, the

command runs the stored procedure. A SqlCommand is an object that allows specifying what

is to be performed in the database.

Access database at runtime using ADO.NET

SqlConnection sqlCon = new SqlConnection(connectionString)

sqlCon.Open();

string strQuery = "select CategoryName from abcd";

SqlCommand cmd = new SqlCommand(strQuery, conn);

SqlDataReader reader = cmd.ExecuteReader();

while (reader.Read())

{       

    Console.WriteLine(reader [0]);  

  }

reader.Close();

con.Close();

16.  Difference between dataset and datareader.

 Dataset

DataSet object can contain multiple rowsets from the same data source as well as from the

relationships between them Dataset is a disconnected architecture Dataset can persist data.

Datareader

DataReader provides forward-only and read-only access to data.Datareader is connected architecture Datareader can not persist data.

Difference between dataset and datareader.

Dataset

a. Disconnected

b. Can traverse data in any order front, back.

c. Data can be manipulated within the dataset.

d. More expensive than datareader as it stores multiple rows at the same time.

Datareader

a. Connection needs to be maintained all the time

b. Can traverse only forward.

c. It is read only therefore, data cannot be manipulated.

d. It is less costly because it stores one row at a time

17.  Command objects uses, purposes and their methods.

    The command objects are used to connect to the Datareader or dataset objects with the

help of the following methods:

ExecuteNonQuery:

This method executes the command defined in the CommandText property.The connection used is defined in the Connection property for a query.It returns an Integer indicating the number of rows affected by the query.

ExecuteReader:

This method executes the command defined in the CommandText property.The connection used is defined in the Connection property. It returns a reader object that is connected to the resulting rowset within the database, allowing the rows to be retrieved.

ExecuteScalar:

This method executes the command defined in the CommandText property.The connection used is defined in the Connection property. It returns a single value which is the first column of the first row of the resulting rowset.The rows of the rest of the result are discarded. It is fast and efficient in cases where a singleton value is required.

Command objects uses, purposes and their methods. Command objects are used to execute the queries, procedures. Sql statements etc. It can execute stored procedures or queries that use parameters as well.

It works on the basis of certain properties like ActiveConnection, CommandText, CommandType, Name etc.

Command object has three methods:

a) Execute: executes the queries, stored procedures etc.

b) Cancel: stops the method execution

c) CreateParameter: to create a parameter object

18.  Explain the use of data adapter.

The data adapter objects connect a command objects to a Dataset object. They provide the means for the exchange of data between the data store and the tables in the DataSet.

An OleDbDataAdapter object is used with an OLE-DB provider A SqlDataAdapter object uses Tabular Data Services with MS SQL Server.

19.Explain the use of data adapter.

Data adapters are the medium of communication between datasource like database and dataset. It allows activities like reading data, updating data.

20.  What are basic methods of Dataadapter?

The most commonly used methods of the DataAdapter are:

Fill:

This method executes the SelectCommand to fill the DataSet object with data from the data

source.

Depending on whether there is a primary key in the DataSet, the ‘fill’ can also be used to

update an existing table in a DataSet with changes made to the data in the original datasource.

FillSchema

This method executes the SelectCommand to extract the schema of a table from the data

source.

It creates an empty table in the DataSet object with all the corresponding constraints.

Update

This method executes the InsertCommand, UpdateCommand, or DeleteCommand to update

the original data source with the changes made to the content of the DataSet.

21.Explain the basic methods of Dataadapter

Some basic methods of dataadpater are:

a. Fill: adds or updates the rows to dataset from the datasource

b. FillSchema: adds a datatable with the sameschema as in the datasource

c. Update: it calls insert, update, delete sql commands for transferring all the changes from the

dataset to the datasource

d. Dispose : releases all the resources

22.  What is Dataset object? Explain the various objects in Dataset?

The DataSet object is a disconnected storage.It is used for manipulation of relational data. The DataSet is filled with data from the storeWe fill it with data fetched from the data store. Once the work is done with the dataset, connection is reestablished and the changes are reflected back into the store.

Dataset has a collection of Tables which has DataTable collection which further has DataRow

DataColumn objects collections.

It also has collections for the primary keys, constraints, and default values called as constraint

collection. A DefaultView object for each table is used to create a DataView object based on the table, so that the data can be searched, filtered or otherwise manipulated while displaying the data.

23.What is Dataset object? Explain the various objects in Dataset.

The DataSet object represents imported or linked data from an application e.g. manually created Pushpins etc. This object is invalidated once the application is closed. Dataset contains another collection known as DataTable object. Each DataTable contains a collection of DataRow objects and each DataRow is a collection of DataColumn objects.

24. What are the steps involved to fill a dataset?

The DataSet object is a disconnected storage.It is used for manipulation of relational data. The DataSet is filled with data from the store We fill it with data fetched from the data store. Once the work is done with the dataset, connection is reestablished and the changes are reflected back into the store.

What are the steps involved to fill a dataset?

a. Create a connection object.

b. Create an adapter by passing the string query and the connection object as parameters.

c. Create a new object of dataset.

d. Call the Fill method of the adapter and pass the dataset object.

Example:

VB.NET Code:-

Dim strSQL as String

strSQL = "SELECT * from tbl"

Dim sqlCmd As New SqlCommand(strSQL, sqlConn)

Dim sda As New SqlDataAdapter(sqlCmd)

Dim ds As New DataSet

sda.Fill(ds)

24. How can we check that some changes have been made to dataset since it was loaded?

The changes made to the dataset can be tracked using the GetChanges and HasChanges

methods.The GetChanges returns dataset which are changed since it was loaded or since

Acceptchanges was executed. The HasChanges property indicates if any changes were made to the dataset since it was loaded or if acceptchanges method was executed.The RejectChanges can be used to revert thee changes made to the dataset since it was

loaded.

How can we check that some changes have been made to dataset since it was loaded?

a. GetChanges: gives the dataset that has changed since newly loaded or since Accept

changes has been executed.

b. HasChanges: this returns a status that tells if any changes have been made to the dataset

since accept changes was executed.

25.  How can we add/remove row’s in “DataTable” object of “DataSet”?

‘NewRow’ method is provided by the ‘Datatable’ to add new row to it. ‘DataTable’ has DataRowCollection” object which has all rows in a “DataTable” object. Add method of the DataRowCollection is used to add a new row in DataTable.We fill it with data fetched from the data store. Once the work is done with the dataset, connection is reestablished Remove method of the DataRowCollection is used to remove a ‘DataRow’ object from

‘DataTable’. RemoveAt method of the DataRowCollection is used to remove a ‘DataRow’ object from  DataTable’ per the index specified in the DataTable.

26.How can we add/remove row’s in “DataTable” object of “DataSet”?

Datatable has a “NewRow” method that allows addition of a new row to the datatable.

27. How do we use stored procedure in ADO.NET and how do we provide parameters to the stored procedures?

CREATE PROCEDURE RUPDATE (@RID INTEGER, @RDESC NCHAR(50))

AS

SET NOCOUNT OFF

UPDATE Region

SET RDESC = @RDESC

SqlCommand command = new SqlCommand("RUPDATE",con);

command.CommandType = CommandType.StoredProcedure;

command.Parameters.Add(new SqlParameter("@RID",SqlDbType.Int,0,"RID"));

command.Parameters.Add(new SqlParameter("@RDESC",SqlDbType.NChar,50,"RDESC"));

command.Parameters[0].Value=4;

command.Parameters[1].Value="SouthEast";

int i=command.ExecuteNonQuery();

How do we use stored procedure in ADO.NET and how do we provide parameters to the

stored procedures?

SqlCommand cmd1 = new SqlCommand("Employee", conn); Employee is the name of the

stored procedure

cmd.CommandType = CommandType.StoredProcedure;

cmd.Parameters.Add(new SqlParameter("@empID", empId));

28. Explain the basic use of “DataView” and explain its methods.

 A DataView is a representation of a full table or a small section of rows.It is used to sort and find data within Datatable.

Following are the methods of a DataView:

Find : Parameter: An array of values; Value Returned: Index of the row

FindRow : Parameter: An array of values; Value Returned: Collection of DataRow

AddNew : Adds a new row to the DataView object.

Delete : Deletes the specified row from DataView object

29.Explain the basic use of “DataView” and explain its methods.

It is a customizable view of a datatable that allows filtering, searching, editing, navigation.

DataView method:

a. AddNew: To add a new row to the DataView.

b. BeginInit: Begins the initialization of a DataView.

c. CopyTo: items are copied into an array.

d. Delete: Used to delete a row at the specified position.

e. Dispose: Releases the resources.

f. EndInit: Ends the initialization of a DataView.

g. Equals: Compares object instances are equal or not.

h. Find: Finds a specific row in the DataView.

i. FindRows: Returns an array of DataRowView

j. GetEnumerator: Gets an enumerator.

k. GetHashCode: it is used in hashing algorithms.

l. GetService : fetches the implementer of the IServiceProvider.

m. GetType : fetches the current instance type.

n. ToString : Returns a String.

o. Close: Used to close a DataView.

p. ColumnCollectionChanged: Occurs after a DataColumnCollection is successfully changed

q. Dispose: can be overloaded

 r. Finalize: Used to free resources and cleanup before objects are handeled by garbage

collection.

s. IndexListChanged: This event tab=kes place when DataView has been changed successfully.

t. MemberwiseClone : Creates a shallow copy.

u. OnListChanged: Raises the ListChanged event.

v. Open: To open a DataView. 

30.  Differences between “DataSet” and “DataReader”.

Dataset

DataSet object can contain multiple rowsets from the same data source as well as from the

relationships between them Dataset is a disconnected architecture

Dataset can persist data.A DataSet is well suited for data that needs to be retrieved from multiple tables.Due to overhead DatsSet is slower than DataReader.

Datareader

DataReader provides forward-only and read-only access to data.Datareader is connected architecture. It has live connection while reading data Datareader can not persist data.Speed performance is better in DataReader.

31.  Explain how to load multiple tables in a DataSet.

 MyDataSet myds = new MyDataSet();

SqlDataAdapter myda = new SqlDataAdapter ("procId", this.Connection);

myda.SelectCommand.CommandType = CommandType.StoredProcedure;

myda.SelectCommand.Parameters.AddWithValue ("@pId", pId);

myda.TableMappings.Add ("Table", myds.xval.TableName);

myda.Fill (myds);

ADO.NET Code showing Dataset storing multiple tables.

DataSet ds = new DataSet();

ds.Tables.Add(dt1);

ds.Tables.Add(dt2);

ds.Tables.Add(dtn);

32.  What is the use of CommandBuilder?

CommandBuilder builds “Parameter” objects automatically.

Example:

Dim pobjCommandBuilder As New OleDbCommandBuilder(pobjDataAdapter)

pobjCommandBuilder.DeriveParameters(pobjCommand)

If DeriveParameters method is used, an extra trip to the Datastore is madewhich can highly

affect the efficiency.

33.What is the use of CommandBuilder?

CommandBuilder is used to build complex queries. It can even build commands that are based

on the returned results. CommandBuilder is less error prone and more readable than the command object.

34. What’s difference between “Optimistic” and “Pessimistic” locking?

In pessimistic locking, when a user opens a data to update it, a lock is granted. Other users

can only view the data until the whole transaction of the data update is completed.In optimistic locking, a data is opened for updating by multiple users. A lock is granted only during the update transaction and not for the entire session. Due to this concurrency is increased and is a practical approach of updating the data.

What’s difference between “Optimistic” and “Pessimistic” locking?

Pessimistic locking: On updating the data, the record gets locked and no one else can access

that record for updating. It becomes a read-only record till the lock is released. Once the lock

gets released, the record can be locked again and get updated for a different user.

Optimistic locking: This allows multiple user to open up the same record for updation . Record

gets locked only while updating the record. This is the most preferred way of locking for the

web application.

35. How can we perform transactions in .NET?

Following are the general steps that are followed during a transaction:

Open connection

Begin Transaction: the begin transaction method provides with a connection object this can be

used to commit or rollback.

Execute the SQL commands

Commit or roll back

Close the database connection

36.How can we perform transactions in .NET?

Steps to perform a transaction

a. Call the Begin Transaction. This marks the beginning of the transaction.

b. Assign the Transaction object returned by Begin Transaction to the Transaction property of

the SqlCommand.

c. Execute the command.

d. Call the Commit method from SqlTransaction object to save the changes made to the data

through the transaction. Call Rollback undo all the transaction which belong to this transaction.

37. What is connection pooling and what is the maximum Pool Size in ADO.NET Connection String?

A connection pool is created when a connection is opened the first time. The next time a

connection is opened, the connection string is matched and if found exactly equal, the

connection pooling would work.Otherwise, a new connection is opened, and connection pooling won't be used.Maximum pool size is the maximum number of connection objects to be pooled.

If the maximum pool size is reached, then the requests are queued until some connections are

released back to the pool. It is therefore advisable to close the connection once done with it.

What is connection pooling and what is the maximum Pool Size in ADO.NET Connection

String?

Connection pooling is a method of reusing the active database connections instead of creating

new ones every time the user request one. Connection pool manager keeps track of all the

open connections. When a new request comes in, the pool manager checks if there exists any

unused connections and returns one if available. If all connections are busy and the maximum

pool size has not been reached, a new connection is formed and added to the pool. And if the

max pool size is reached, then the requests gets queued up until a connection in the pool

becomes available or the connection attempt times out.

Connection pooling behavior is controlled by the connection string parameters. The following

are four parameters that control most of the connection pooling behavior:

Default max pool size is 100.

38. Can you explain how to enable and disable connection pooling?

Set Pooling=true. However, it is enabled by default in .NET.

To disable connection pooling set Pooling=false in connection string if it is an ADO.NET

Connection.

If it is an OLEDBConnection object set OLEDB Services=-4 in the connection string.

Can you explain how to enable and disable connection pooling?

To enable connection pooling:

SqlConnection myConnection = new SqlConnection(@"Data Source=(local)

\SQLEXPRESS;Initial Catalog=TEST;Integrated Security=SSPI;");

This has connection pooling on by default

To disable connection pooling:

SqlConnection myConnection = new SqlConnection(@"Data Source=(local)

\SQLEXPRESS;Initial Catalog=TEST;Integrated Security=SSPI;Pooling=false;");

Object Pooling

The COM+ Object Pooling service enables you to reduce the overhead of creating each object from scratch. When an object is activated, it is pulled from the pool. When the object is deactivated, it is placed back into the pool to await the next request.
You can configure object pooling by applying the ObjectPoolingAttribute attribute to a class that derives from the System.EnterpriseServices.ServicedComponent class.
Object pooling lets you control the number of connections you use, as opposed to connection pooling, where you control the maximum number reached. Following are important differences between object pooling and connection pooling:

• Creation. When using connection pooling, creation is on the same thread, so if there is nothing in the pool, a connection is created on your behalf. With object pooling, the pool might decide to create a new object. However, if you have already reached your maximum, it instead gives you the next available object. This is crucial behavior when it takes a long time to create an object, but you do not use it for very long.
• Enforcement of minimums and maximums. This is not done in connection pooling. The maximum value in object pooling is very important when trying to scale your application. You might need to multiplex thousands of requests to just a few objects. (TPC/C benchmarks rely on this.)

COM+ object pooling is practically identical to .NET Framework managed SQL Client connection pooling. For example, creation is on a different thread and minimums and maximums are enforced.

Note   Application domains affect the behavior of object pooling. In Microsoft Windows 2000, when application activation is set to Library and you have multiple application domains, pooled objects are all created in the default application domain and shared between multiple clients. In the same situation, using Microsoft Windows XP and Windows Server 2003, there is one object pool per application domain. Using either operating system with multiple application domains and your application activation set to server, out-of-process clients use the object pool in the default application domain.                                                 By.http://msdn.microsoft.com

Code 1: Object Pool and Employee class.

 

using System;

using System.Collections;

 

namespace ObjectPooling

{

    class Factory

    {

        // Maximum objects allowed!

        private static int _PoolMaxSize = 2;

 

        // My Collection Pool

        private static readonly Queue objPool = new Queue(_PoolMaxSize);  

 

        public Employee GetEmployee()

        {

            Employee oEmployee;

 

            // check from the collection pool. If exists return object else create new

            if (Employee.Counter >= _PoolMaxSize && objPool.Count>0)

            {

                // Retrieve from pool

                oEmployee = RetrieveFromPool();

            }

            else

            {

                oEmployee = GetNewEmployee();

            }

            return oEmployee;

        }

 

        private Employee GetNewEmployee()

        {

            // Creates a new employee

            Employee oEmp = new Employee();

            objPool.Enqueue(oEmp);

            return oEmp;

        }

       

        protected Employee RetrieveFromPool()

        {

            Employee oEmp;

 

            // if there is any objects in my collection

            if (objPool.Count>0)

            {

                oEmp = (Employee)objPool.Dequeue();

                Employee.Counter--;

            }

            else

            {

                // return a new object

                oEmp = new Employee();

            }

            return oEmp;

        }

    }

 

    class Employee

    {

        public static int Counter = 0;

        public Employee()

        {

            ++Counter;

        }

 

        private string _Firstname;

        public string Firstname

        {

            get

            {

                return _Firstname;

            }

            set

            {

                _Firstname = value;

            }

        } 

    }

}

 

Code 2: How to use it?

 

private void button1_Click(object sender, EventArgs e)

{

    Factory fa = new Factory();

 

    Employee myEmp = fa.GetEmployee();

    Console.WriteLine("First object");

 

    Employee myEmp1 = fa.GetEmployee();

    Console.WriteLine("Second object")

}

Dot Net Framework Interview Questions

1.What is the Microsoft.NET?

.NET is a set of technologies designed to transform the internet into a full scale distributed platform. It provides new ways of connecting systems, information and devices through a collection of web services. It also provides a language independent, consistent programming model across all tiers of an application.

The goal of the .NET platform is to simplify web development by providing all of the tools and technologies that one needs to build distributed web applications.

2.What is the .NET Framework?

The .NET Framework is set of technologies that form an integral part of the .NET Platform. It is Microsoft's managed code programming model for building applications that have visually stunning user experiences, seamless and secure communication, and the ability to model a range of business processes.

The .NET Framework has two main components: the common language runtime (CLR) and .NET Framework class library. The CLR is the foundation of the .NET framework and provides a common set of services for projects that act as building blocks to build up applications across all tiers. It simplifies development and provides a robust and simplified environment which provides common services to build application. The .NET framework class library is a collection of reusable types and exposes features of the runtime. It contains of a set of classes that is used to access common functionality.

3.What is CLR?

The .NET Framework provides a runtime environment called the Common Language Runtime or CLR. The CLR can be compared to the Java Virtual Machine or JVM in Java. CLR handles the execution of code and provides useful services for the implementation of the program. In addition to executing code, CLR provides services such as memory management, thread management, security management, code verification, compilation, and other system services. It enforces rules that in turn provide a robust and secure execution environment for .NET applications.

4.What is CTS?

Common Type System (CTS) describes the datatypes that can be used by managed code. CTS defines how these types are declared, used and managed in the runtime. It facilitates cross-language integration, type safety, and high performance code execution. The rules defined in CTS can be used to define your own classes and values.

5.What is CLS?

Common Language Specification (CLS) defines the rules and standards to which languages must adhere to in order to be compatible with other .NET languages. This enables C# developers to inherit from classes defined in VB.NET or other .NET compatible languages.

6.What is managed code?

The .NET Framework provides a run-time environment called the Common Language Runtime, which manages the execution of code and provides services that make the development process easier. Compilers and tools expose the runtime's functionality and enable you to write code that benefits from this managed execution environment. The code that runs within the common language runtime is called managed code.

7.What is MSIL?

When the code is compiled, the compiler translates your code into Microsoft intermediate language (MSIL). The common language runtime includes a JIT compiler for converting this MSIL then to native code.

MSIL contains metadata that is the key to cross language interoperability. Since this metadata is standardized across all .NET languages, a program written in one language can understand the metadata and execute code, written in a different language. MSIL includes instructions for loading, storing, initializing, and calling methods on objects, as well as instructions for arithmetic and logical operations, control flow, direct memory access, exception handling, and other operations.

8.What is JIT?

JIT is a compiler that converts MSIL to native code. The native code consists of hardware specific instructions that can be executed by the CPU.

Rather than converting the entire MSIL (in a portable executable[PE]file) to native code, the JIT converts the MSIL as it is needed during execution. This converted native code is stored so that it is accessible for subsequent calls.

9.What is portable executable (PE)?PE is the file format defining the structure that all executable files (EXE) and Dynamic Link Libraries (DLL) must use to allow them to be loaded and executed by Windows. PE is derived from the Microsoft Common Object File Format (COFF). The EXE and DLL files created using the .NET Framework obey the PE/COFF formats and also add additional header and data sections to the files that are only used by the CLR.

10.What is an application domain?

Application domain is the boundary within which an application runs. A process can contain multiple application domains. Application domains provide an isolated environment to applications that is similar to the isolation provided by processes. An application running inside one application domain cannot directly access the code running inside another application domain. To access the code running in another application domain, an application needs to use a proxy.

11.How does an AppDomain get created? AppDomains are usually created by hosts. Examples of hosts are the Windows Shell, ASP.NET and IE. When you run a .NET application from the command-line, the host is the Shell. The Shell creates a new AppDomain for every application. AppDomains can also be explicitly created by .NET applications.

12.What is an assembly?

An assembly is a collection of one or more .exe or dll’s. An assembly is the fundamental unit for application development and deployment in the .NET Framework. An assembly contains a collection of types and resources that are built to work together and form a logical unit of functionality. An assembly provides the CLR with the information it needs to be aware of type implementations.

13.What are the contents of assembly?

A static assembly can consist of four elements:

·         Assembly manifest - Contains the assembly metadata. An assembly manifest contains the information about the identity and version of the assembly. It also contains the information required to resolve references to types and resources.

·         Type metadata - Binary information that describes a program.

·         Microsoft intermediate language (MSIL) code.

·         A set of resources.

14.What are the different types of assembly?

Assemblies can also be private or shared. A private assembly is installed in the installation directory of an application and is accessible to that application only. On the other hand, a shared assembly is shared by multiple applications. A shared assembly has a strong name and is installed in the GAC.

We also have satellite assemblies that are often used to deploy language-specific resources for an application.

15.What is a dynamic assembly?

A dynamic assembly is created dynamically at run time when an application requires the types within these assemblies.

16.What is a strong name?

You need to assign a strong name to an assembly to place it in the GAC and make it globally accessible. A strong name consists of a name that consists of an assembly's identity (text name, version number, and culture information), a public key and a digital signature generated over the assembly.  The .NET Framework provides a tool called the Strong Name Tool (Sn.exe), which allows verification and key pair and signature generation.

17.What is GAC? What are the steps to create an assembly and add it to the GAC?

The global assembly cache (GAC) is a machine-wide code cache that stores assemblies specifically designated to be shared by several applications on the computer. You should share assemblies by installing them into the global assembly cache only when you need to.

Steps

- Create a strong name using sn.exe tool eg: sn -k mykey.snk

- in AssemblyInfo.cs, add the strong name eg: [assembly: AssemblyKeyFile("mykey.snk")]

- recompile project, and then install it to GAC in two ways :

·         drag & drop it to assembly folder (C:\WINDOWS\assembly OR C:\WINNT\assembly) (shfusion.dll tool)

·         gacutil -i abc.dll

18.What is the caspol.exe tool used for?

The caspol tool grants and modifies permissions to code groups at the user policy, machine policy, and enterprise policy levels.

19.What is a garbage collector?

A garbage collector performs periodic checks on the managed heap to identify objects that are no longer required by the program and removes them from memory.

20.What are generations and how are they used by the garbage collector?

Generations are the division of objects on the managed heap used by the garbage collector. This mechanism allows the garbage collector to perform highly optimized garbage collection. The unreachable objects are placed in generation 0, the reachable objects are placed in generation 1, and the objects that survive the collection process are promoted to higher generations.

21.What is Ilasm.exe used for?

Ilasm.exe is a tool that generates PE files from MSIL code. You can run the resulting executable to determine whether the MSIL code performs as expected.

22.What is Ildasm.exe used for?

Ildasm.exe is a tool that takes a PE file containing the MSIL code as a parameter and creates a text file that contains managed code.

23.What is the ResGen.exe tool used for?

ResGen.exe is a tool that is used to convert resource files in the form of .txt or .resx files to common language runtime binary .resources files that can be compiled into satellite assemblies.

24.What is CODE Access security?
CAS is part of .NET security model that determines whether or not a piece of code is allowed to run and what resources it can use while running. Example CAS will allow an application to read but not to write and delete a file or a resource from a folder.

25.What is reflection?
All .NET assemblies have metadata information stored about the types defined in modules. This metadata information can be accessed by mechanism called as "Reflection".System. Reflection can be used to browse through the metadata information.                                                                     

Software design pattern

a design pattern is a general reusable solution to a commonly occurring problem within a given context insoftware design. It is a description or template for how to solve a problem that can be used in many different situations. Patterns are formalized best practices that the programmer must implement themselves in the application.^[1] Object-oriented design patterns typically show relationships andinteractions between classes or objects, without specifying the final application classes or objects that are involved. Many patterns imply object-orientation or more generally mutable state, and so may not be as applicable in functional programming languages, in which data is immutable or treated as such.
Design patterns reside in the domain of modules and interconnections. At a higher level there are architectural patterns that are larger in scope, usually describing an overall pattern followed by an entire system.

Design Pattern Type 

Creational

Creational patterns are ones that create objects for you, rather than having you instantiate objects directly. This gives your program more flexibility in deciding which objects need to be created for a given case.

• Abstract Factory groups object factories that have a common theme.
• Builder constructs complex objects by separating construction and representation.
• Factory Method creates objects without specifying the exact class to create.
• Prototype creates objects by cloning an existing object.
• Singleton restricts object creation for a class to only one instance.

[edit]Structural

These concern class and object composition. They use inheritance to compose interfaces and define ways to compose objects to obtain new functionality.

• Adapter allows classes with incompatible interfaces to work together by wrapping its own interface around that of an already existing class.
• Bridge decouples an abstraction from its implementation so that the two can vary independently.
• Composite composes zero-or-more similar objects so that they can be manipulated as one object.
• Decorator dynamically adds/overrides behaviour in an existing method of an object.
• Facade provides a simplified interface to a large body of code.
• Flyweight reduces the cost of creating and manipulating a large number of similar objects.
• Proxy provides a placeholder for another object to control access, reduce cost, and reduce complexity.

[edit]Behavioral

Most of these design patterns are specifically concerned with communication between objects.

• Chain of responsibility delegates commands to a chain of processing objects.
• Command creates objects which encapsulate actions and parameters.
• Interpreter implements a specialized language.
• Iterator accesses the elements of an object sequentially without exposing its underlying representation.
• Mediator allows loose coupling between classes by being the only class that has detailed knowledge of their methods.
• Memento provides the ability to restore an object to its previous state (undo).
• Observer is a publish/subscribe pattern which allows a number of observer objects to see an event.
• State allows an object to alter its behavior when its internal state changes.
• Strategy allows one of a family of algorithms to be selected on-the-fly at runtime.
• Template method defines the skeleton of an algorithm as an abstract class, allowing its subclasses to provide concrete behavior.
• Visitor separates an algorithm from an object structure by moving the hierarchy of methods into one object.