Technical Posts

Attributes - Dot Net Interview Questions Part VI

2010-07-17T15:20:00.000+05:30

7.1 What are attributes?

There are at least two types of .NET attribute. The first type I will refer to as a metadata attribute - it allows some data to be attached to a class or method. This data becomes part of the metadata for the class, and (like other class metadata) can be accessed via reflection. An example of a metadata attribute is [serializable], which can be attached to a class and means that instances of the class can be serialized.

[serializable] public class CTest {}

The other type of attribute is a context attribute. Context attributes use a similar syntax to metadata attributes but they are fundamentally different. Context attributes provide an interception mechanism whereby instance

activation and method calls can be pre- and/or post-processed. If you have encountered Keith Brown's universal delegator you'll be familiar with this idea.

==========================================================================

7.2 Can I create my own metadata attributes?

Yes. Simply derive a class from System.Attribute and mark it with the AttributeUsage attribute. For example:

[AttributeUsage(AttributeTargets.Class)]

public class InspiredByAttribute : System.Attribute {

public string InspiredBy;

public InspiredByAttribute( string inspiredBy ){

InspiredBy = inspiredBy;

}

[InspiredBy("Andy Mc's brilliant .NET FAQ")]

class CTest{

}

class CApp{

public static void Main(){

object[] atts = typeof(CTest).GetCustomAttributes(true);

foreach( object att in atts )

if( att is InspiredByAttribute )

Console.WriteLine( "Class CTest was inspired by {0}",

((InspiredByAttribute)att).InspiredBy );

}

==========================================================================

Code Access Security

7.3 What is Code Access Security (CAS)?

CAS is the part of the .NET security model that determines whether or not code is allowed to run, and what resources it can use when it is running. For example, it is CAS that will prevent a .NET web applet from formatting your hard disk.

==========================================================================

7.4 How does CAS work?

The CAS security policy rev olves around two key concepts - code groups and permissions. Each .NET assembly is a member of a particular code group, and each code group is granted the permissions specified in a named permission set.

For example, using the default security policy, a control downloaded from a web site belongs to the 'Zone - Internet' code group, which adheres to the permissions defined by the 'Internet' named permission set. (Naturally the 'Internet' named permission set represents a very restrictive range of permissions.)

==========================================================================

7.5 Who defines the CAS code groups?

Microsoft defines some default ones, but you can modify these and even create your own. To see the code groups defined on your system,

run 'caspol -lg' from the command-line.

On my system it looks like this:

Level = Machine

Code Groups:

1. All code: Nothing

1.1. Zone - MyComputer: FullTrust

1.1.1. Honor SkipVerification requests: SkipVerification

1.2. Zone - Intranet: LocalIntranet

1.3. Zone - Internet: Internet

1.4. Zone - Untrusted: Nothing

1.5. Zone - Trusted: Internet

1.6. StrongName -

0024000004800000940000000602000000240000525341310004000003

000000CFCB3291AA715FE99D40D49040336F9056D7886FED46775BC7BB5430BA4444FEF834

8EBD06

F962F39776AE4DC3B7B04A7FE6F49F25F740423EBF2C0B89698D8D08AC48D69CED0FC8F83B

465E08

07AC11EC1DCC7D054E807A43336DDE408A5393A48556123272CEEEE72F1660B71927D3856

1AABF5C

AC1DF1734633C602F8F2D5: Everything

Note:

The hierarchy of code groups - the top of the hierarchy is the most general ('All code'), which is then sub-divided into several groups, each of which in turn can be sub-divided. Also note that (somewhat counterintuitively) a sub-group can be associated with a more permissive permission set than its parent.

==========================================================================

7.6 How do I define my own code group?

Use caspol. For example, suppose you trust code from http://www.mydomain.com/ and you want it have full access to your system, but you want to keep the default restrictions for all other internet sites. To achieve this, you would add a new code group as a sub-group of the 'Zone - Internet' group, like this:

caspol -ag 1.3 -site www.mydomain.com FullTrust

Now if you run caspol -lg you will see that the new group has been added as group 1.3.1:

...

1.3. Zone - Internet: Internet

1.3.1. Site - www.mydomain.com: FullTrust

...

Note that the numeric label (1.3.1) is just a caspol invention to make the code groups easy to manipulate from the command-line. The underlying runtime never sees it.

==========================================================================

7.7 How do I change the permission set for a code group?

Use caspol. If you are the machine administrator, you can operate at the 'machine' level - which means not only that the changes you make become the default for the machine, but also that users cannot change the

permissions to be more permissive. If you are a normal (non-admin) user you can still modify the permissions, but only to make them more restrictive.

For example, to allow intranet code to do what it likes you might do this:

caspol -cg 1.2 FullTrust

Note that because this is more permissive than the default policy (on a standard system), you should only do this at the machine level - doing it at the user level will have no effect.

==========================================================================

7.8 I'm having some trouble with CAS. How can I troubleshoot the problem?

Caspol has a couple of options that might help. First, you can ask caspol to tell you what code group an assembly belongs to, using caspol -rsg. Similarly, you can ask what permissions are being applied to a particular assembly using caspol -rsp.

===========================================================================

7.9 I can't be bothered with CAS. Can I turn it off?

Yes, as long as you are an administrator. Just run:

caspol -s off

==========================================================================

Three (3) Tier Architecture Versus Four (4) Tier Architecture - General Introduction

2010-07-14T17:49:00.029+05:30

THREE TIER ARCHITECTURE

3-Tier architecture generally contains UI or Presentation Layer, Business Access Layer (BAL) or Business Logic Layer and Data Access Layer (DAL).

Presentation Layer (UI)
Presentation layer cotains pages like .aspx or windows form where data is presented to the user or input is taken from the user.

Business Access Layer (BAL) or Business Logic Layer
BAL contains business logic, validations or calculations related with the data, if needed. I will call it Business Access Layer in my demo.

Data Access Layer (DAL)
DAL contains methods that helps business layer to connect the data and perform required action, might be returning data or manipulating data (insert, update, delete etc). For this demo application, I have taken a very simple example. I am assuming that I have to play with record of persons (FirstName, LastName, Age) and I will refer only these data through out this article.

===================================================================

FOUR TIER ARCHITECTURE

Four Tier Architecture is just an enhancement of 3-Tier archicture. In this architecture; no need of writing long function parameters throughout the layers (as in traditionally 3-Tier archicture has to) and the actual objects of the application will be in a separate tier so that in future it can separately use these objects for enhancements. Change in the object definition can be done without touching the entire Business Access Layers.

Process of creatioin of 4-Tier architecture application.

Take an example of a Person that will have 3 properties: FirstName, LastName, Age. Create a separate pages to insert these records (default.aspx) into database and list, update, delete records (list.aspx) from database.

In this application there are 4-Tiers presents,

1. Business Object [BO]
2. Business Access Layer [BAL]
3. Data Access Layer [DAL]
4. UI (4-Tier) folder [UI]

===================================================================

Serialization - Dot Net Interview Questions Part V

2010-07-14T16:27:00.008+05:30

6.1 What is serialization?

Serialization is the process of converting an object into a stream of bytes. Deserialization is the opposite process, i.e. creating an object from a stream of bytes. Serialization/Deserialization is mostly used to transport objects (e.g. during remoting), or to persist objects (e.g. to a file or database).

====================================================================

6.2 Does the .NET Framework have in-built support for serialization?

There are two separate mechanisms provided by the .NET class library - XmlSerializer and SoapFormatter/BinaryFormatter. Microsoft uses XmlSerializer for Web Services, and SoapFormatter/BinaryFormatter for remoting. Both are available for use in your own code.

====================================================================

3.3 I want to serialize instances of my class. Should I use XmlSerializer, SoapFormatter or BinaryFormatter?

It depends. XmlSerializer has severe limitations such as the requirement that the target class has a parameterless constructor, and only public read/write properties and fields can be serialized. However, on the plus side, XmlSerializer has good support for customising the XML document that is produced or consumed.

XmlSerializer's features mean that it is most suitable for cross-platform work, or for constructing objects from existing XML documents. SoapFormatter and BinaryFormatter have fewer limitations than XmlSerializer. They can serialize private fields, for example. However they both require that the target class be marked with the [Serializable] attribute,so like XmlSerializer the class needs to be written with serialization in mind.

Also there are some quirks to watch out for - for example on deserialization the constructor of the new object is not invoked. The choice between SoapFormatter and BinaryFormatter depends on the application. BinaryFormatter makes sense where both serialization and deserialization will be performed on the .NET platform and where performance is important. SoapFormatter generally makes more sense in all other cases, for ease of debugging if nothing else.

====================================================================

6.4 Can I customise the serialization process?

Yes. XmlSerializer supports a range of attributes that can be used to configure serialization for a particular class. For example, a field or property can be marked with the [XmlIgnore] attribute to exclude it from serialization. Another example is the [XmlElement] attribute, which can be used to specify the XML element name to be used for a particular property or field. Serialization via SoapFormatter/BinaryFormatter can also be controlled to some extent by attributes. For example, the [NonSerialized] attribute is the equivalent of XmlSerializer's [XmlIgnore] attribute. Ultimate control of the serialization process can be acheived by implementing the the ISerializable interface on the class whose instances are to be serialized.

====================================================================

6.5 Why is XmlSerializer so slow?

There is a once-per-process-per-type overhead with XmlSerializer. So the first time you serialize or deserialize an object of a given type in an application, there is a significant delay. This normally doesn't matter, but it may mean, for example, that XmlSerializer is a poor choice for loading configuration settings during startup of a GUI application.

====================================================================

6.6 Why do I get errors when I try to serialize a Hashtable?

XmlSerializer will refuse to serialize instances of any class that implements IDictionary, e.g. Hashtable. SoapFormatter and BinaryFormatter do not have this restriction.

====================================================================

6.7 XmlSerializer is throwing a generic "There was an errorreflecting MyClass" error. How do I find out what the problem is?

Look at the InnerException property of the exception that is thrown to get a more specific error message.

====================================================================

6.8 Why am I getting an InvalidOperationException when I serialize an ArrayList?

XmlSerializer needs to know in advance what type of objects it will find in an ArrayList. To specify the type, use the XmlArrayItem attibute like this:

public class Person

{
public string Name;
public int Age;
}

public class Population

{
[XmlArrayItem(typeof(Person))] public ArrayList People;
}

====================================================================

Garbage Collections - Dot Net Interview Question Part IV

2010-07-13T10:39:00.007+05:30

5.1 What is garbage collection?

Garbage collection is a heap-management strategy where a run-time component takes responsibility for managing the lifetime of the memory used by objects. This concept is not new to .NET - Java and many other languages/runtimes have used garbage collection for some time.

====================================================================

5.2 Is it true that objects don't always get destroyed immediately when the last reference goes away?

Yes. The garbage collector offers no guarantees about the time when an object will be destroyed and its memory reclaimed.

=====================================================================

5.3 Why doesn't the .NET runtime offer deterministic destruction?

Because of the garbage collection algorithm. The .NET garbage collector works by periodically running through a list of all the objects that are currently being referenced by an application. All the objects that it doesn't find during this search are ready to be destroyed and the memory reclaimed. The implication of this algorithm is that the runtime doesn't get notified immediately when the final reference on an object goes away - it only finds out during the next 'sweep' of the heap.

Futhermore, this type of algorithm works best by performing the garbage collection sweep as rarely as possible. Normally heap exhaustion is the trigger for a collection sweep.

=====================================================================

5.4 Is the lack of deterministic destruction in .NET a problem?

It's certainly an issue that affects component design. If you have objects that maintain expensive or scarce resources (e.g. database locks), you need to provide some way to tell the object to release the resource when it is done. Microsoft recommend that you provide a method called Dispose() for this purpose. However, this causes problems for distributed objects - in a distributed system who calls the Dispose() method? Some form of referencecounting or ownership-management mechanism is needed to handle distributed objects - unfortunately the runtime offers no help with this.

====================================================================

5.5 Should I implement Finalize on my class? Should I implement IDisposable?

This issue is a little more complex than it first appears. There are really two categories of class that require deterministic destruction - the first category manipulate unmanaged types directly, whereas the second category manipulate managed types that require deterministic destruction. An example of the first category is a class with an IntPtr member representing an OS file handle. An example of the second category is a class with a System.IO.FileStream member.

For the first category, it makes sense to implement IDisposable and override Finalize. This allows the object user to 'do the right thing' by calling Dispose, but also provides a fallback of freeing the unmanaged resource in the Finalizer, should the calling code fail in its duty. However this logic does not apply to the second category of class, with only managed resources. In this case implementing Finalize is pointless, as managed member objects cannot be accessed in the Finalizer. This is because there is no guarantee about the ordering of Finalizer execution. So only the Dispose method should be implemented. (If you think about it, it doesn't really make sense to call Dispose on member objects from a Finalizer anyway, as the member object's Finalizer will do the required cleanup.) For classes that need to implement IDisposable and override Finalize, see Microsoft's documented pattern.

Note that some developers argue that implementing a Finalizer is always a bad idea, as it hides a bug in your code (i.e. the lack of a Dispose call). A less radical approach is to implement Finalize but include a Debug.Assert at the start, thus signalling the problem in developer builds but allowing the cleanup to occur in release builds.

=====================================================================

5.6 Do I have any control over the garbage collection algorithm?

A little. For example the System.GC class exposes a Collect method, which forces the garbage collector to collect all unreferenced objects immediately. Also there is a gcConcurrent setting that can be specified via the application configuration file. This specifies whether or not the garbage collector performs some of its collection activities on a separate thread. The setting only applies on multi-processor machines, and defaults to true.

=====================================================================

5.7 How can I find out what the garbage collector is doing?

Lots of interesting statistics are exported from the .NET runtime via the '.NET CLR xxx' performance counters. Use Performance Monitor to view them.

=====================================================================

5.8 What is the lapsed listener problem?

The lapsed listener problem is one of the primary causes of leaks in .NET applications. It occurs when a subscriber (or 'listener') signs up for a publisher's event, but fails to unsubscribe. The failure to unsubscribe means that the publisher maintains a reference to the subscriber as long as the publisher is alive. For some publishers, this may be the duration of the application.

This situation causes two problems. The obvious problem is the leakage of the subscriber object. The other problem is the performance degredation due to the publisher sending redundant notifications to 'zombie' subscribers. There are at least a couple of solutions to the problem. The simplest is to make sure the subscriber is unsubscribed from the publisher, typically by adding an Unsubscribe() method to the subscriber. Another solution, documented here by Shawn Van Ness, is to change the publisher to use weak references in its subscriber list.

=====================================================================

Application Domains - Dot Net Interview Questions Part III

2010-07-12T11:12:00.002+05:30

4.1 What is an application domain?
An AppDomain can be thought of as a lightweight process. Multiple AppDomains can exist inside a Win32 process. The primary purpose of the AppDomain is to isolate applications from each other, and so it is particularly useful in hosting scenarios such as ASP.NET. An AppDomain can be destroyed by the host without affecting other AppDomains in the process. Win32 processes provide isolation by having distinct memory address spaces. This is effective, but expensive. The .NET runtime enforces AppDomain isolation by keeping control over the use of memory - all memory in the AppDomain is managed by the .NET runtime, so the runtime can ensure that AppDomains do not access each other's memory. One non-obvious use of AppDomains is for unloading types. Currently the only way to unload a .NET type is to destroy the AppDomain it is loaded into. This is particularly useful if you create and destroy types on-the-fly via reflection.

====================================================================

4.2 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. Here is a C# sample which creates an AppDomain, creates an instance of an object inside it, and then executes one of the object's methods:

using System;
using System.Runtime.Remoting;
using System.Reflection;
public class CAppDomainInfo : MarshalByRefObject
{
public string GetName() { return AppDomain.CurrentDomain.FriendlyName; }
}
public class App
{
public static int Main()
{
AppDomain ad = AppDomain.CreateDomain( "Andy's new domain" );
CAppDomainInfo adInfo = (CAppDomainInfo)ad.CreateInstanceAndUnwrap(
Assembly.GetCallingAssembly().GetName().Name, "CAppDomainInfo" );
Console.WriteLine( "Created AppDomain name = " + adInfo.GetName() );
return 0;
}
}

=====================================================================

4.3 Can I write my own .NET host?

Yes. For an example of how to do this, take a look at the source for the dm.net moniker developed by Jason Whittington and Don Box. There is also a code sample in the .NET SDK called CorHost.

=====================================================================

Assemblies - Dot Net Interview Questions - Part II

2010-07-06T10:00:00.004+05:30

3.1 What is an assembly?

An assembly is sometimes described as a logical .EXE or .DLL, and can be an application (with a main entry point) or a library. An assembly consists of one or more files (dlls, exes, html files etc), and represents a group of resources, type definitions, and implementations of those types. An assembly may also contain references to other assemblies. These resources, types and references are described in a block of data called a manifest. The manifest is part of the assembly, thus making the assembly self-describing. An important aspect of assemblies is that they are part of the identity of a type. The identity of a type is the assembly that houses it combined with the type name. This means, for example, that if assembly A exports a type called

T, and assembly B exports a type called T, the .NET runtime sees these as two completely different types. Furthermore, don't get confused between assemblies and namespaces - namespaces are merely a hierarchical way of organising type names. To the runtime, type names are type names, regardless of whether namespaces are used to organise the names. It's the assembly plus the typename (regardless of whether the type name belongs to a namespace) that uniquely indentifies a type to the runtime. Assemblies are also important in .NET with respect to security - many of the security restrictions are enforced at the assembly boundary.

Finally, assemblies are the unit of versioning in .NET - more on this below.

====================================================================

3.2 How can I produce an assembly?

The simplest way to produce an assembly is directly from a .NET compiler.

For example, the following C# program:

public class CTest

{

public CTest() { System.Console.WriteLine( "Hello from CTest" ); }

}

can be compiled into a library assembly (dll) like this:

csc /t:library ctest.cs

You can then view the contents of the assembly by running the "IL Disassembler" tool that comes with the .NET SDK. Alternatively you can compile your source into modules, and then combine the modules into an assembly using the assembly linker (al.exe). For the C# compiler, the /target:module switch is used to generate a module instead of an assembly.

====================================================================

3.3 What is the difference between a private assembly and a shared assembly?

(I) Location and visibility: A private assembly is normally used by a single application, and is stored in the application's directory, or a subdirectory beneath. A shared assembly is normally stored in the global assembly cache, which is a repository of assemblies maintained by the .NET runtime. Shared assemblies are usually libraries of code which many applications will find useful, e.g. the .NET framework classes.

(II) Versioning: The runtime enforces versioning constraints only on shared assemblies, not on private assemblies.

====================================================================

3.4 How do assemblies find each other?

By searching directory paths. There are several factors which can affect the path (such as the AppDomain host, and application configuration files), but for private assemblies the search path is normally the application's directory and its sub-directories. For shared assemblies, the search path is normally same as the private assembly path plus the shared assembly cache.

====================================================================

3.5 How does assembly versioning work?

Each assembly has a version number called the compatibility version. Also each reference to an assembly (from another assembly) includes both the name and version of the referenced assembly. The version number has four numeric parts (e.g. 5.5.2.33). Assemblies with either of the first two parts different are normally viewed as incompatible. If the first two parts are the same, but the third is different, the assemblies are deemed as 'maybe compatible'. If only the fourth part is different, the assemblies are deemed compatible. However, this is just the default

guideline - it is the version policy that decides to what extent these rules are enforced. The version policy can be specified via the application configuration file.

Remember: versioning is only applied to shared assemblies, not private assemblies.

====================================================================

Dot Net Interview Questions - Dot Net Framework - Part II

2010-07-02T11:35:00.004+05:30

2.1 What is .NET?

DOT NET is a general-purpose software development platform, similar to Java. At its core is a virtual machine that turns intermediate language (IL) into machine code. High-level language compilers for C#, VB.NET and C++ are provided to turn source code into IL. C# is a new programming language, very similar to Java. An extensive class library is included, featuring all the functionality one might expect from a contemporary development platform - windows GUI development (Windows Forms), database access (ADO.NET), web development (ASP.NET), web services, XML etc.

2.2 What operating systems does the .NET Framework run on?

The runtime supports Windows Server 2003, Windows XP, Windows 2000, NT4 SP6a and Windows ME/98. Windows 95 is not supported. Some parts of the framework do not work on all platforms - for example, ASP.NET is only supported on XP and Windows 2000/2003. Windows 98/ME cannot be used for development.

IIS is not supported on Windows XP Home Edition, and so cannot be used to host ASP.NET. However, the ASP.NET Web Matrix web server does run on XP Home. The .NET Compact Framework is a version of the .NET Framework for mobile devices, running Windows CE or Windows Mobile. The Mono project has a version of the .NET Framework that runs on Linux.

2.3 What is the CLI? Is it the same as the CLR?

The CLI (Common Language Infrastructure) is the definition of the fundamentals of the .NET framework - the Common Type System (CTS), metadata, the Virtual Execution Environment (VES) and its use of intermediate language (IL), and the support of multiple programming languages via the Common Language Specification (CLS). The CLI is documented through ECMA

The CLR (Common Language Runtime) is Microsoft's primary implementation of the CLI. Microsoft also have a shared source implementation known as ROTOR, for educational purposes, as well as the .NET Compact Framework for mobile devices. Non-Microsoft CLI implementations include Mono and DotGNU Portable. NET.

2.4 What is the CTS, and how does it relate to the CLS?

CTS : Common Type System. This is the full range of types that the .NET runtime understands. Not all .NET languages support all the types in the CTS.

CLS : Common Language Specification. This is a subset of the CTS which all .NET languages are expected to support. The idea is that any program which uses CLS-compliant types can interoperate with any .NET program written in any language. This interop is very fine-grained - for example a VB.NET class can inherit from a C# class.

2.5 What does 'managed' mean in the .NET context?

The term 'managed' is the cause of much confusion. It is used in various places within .NET, meaning slightly different things. Managed code: The .NET framework provides several core run-time services to the programs that run within it - for example exception handling and security. For these services to work, the code must provide a minimum level of information to the runtime. Such code is called managed code.

Managed data: This is data that is allocated and freed by the .NET runtime's garbage collector.

2.6 What is reflection?

All .NET compilers produce metadata about the types defined in the modules they produce. This metadata is packaged along with the module (modules in turn are packaged together in assemblies), and can be accessed by a mechanism called reflection. The System.Reflection namespace contains classes that can be used to interrogate the types for a module/assembly.
Using reflection to access .NET metadata is very similar to using ITypeLib/ITypeInfo to access type library data in COM, and it is used for similar purposes - e.g. determining data type sizes for marshaling data across context/process/machine boundaries. Reflection can also be used to dynamically invoke methods (see System.Type.InvokeMember), or even create types dynamically at run-time (see System.Reflection.Emit.TypeBuilder).

Basic Dot Net Interview Questions

2010-06-29T15:52:00.003+05:30

(I) What is a IL?
Twist :- What is MSIL or CIL , What is JIT?

(IL)Intermediate Language is also known as MSIL (Microsoft Intermediate Language) or CIL
(Common Intermediate Language). All .NET source code is compiled to IL. This IL is then
converted to machine code at the point where the software is installed, or at run-time by a Just-In-Time (JIT) compiler.
-------------------------------------------------------------------------------------------------
(II) What is a CLR?

Full form of CLR is Common Language Runtime and it forms the heart of the .NET framework.
All Languages have runtime and its the responsibility of the runtime to take care of the code
execution of the program. For example VC++ has MSCRT40.DLL,VB6 has MSVBVM60.DLL,
Java has Java Virtual Machine etc. Similarly .NET has CLR. Following are the responsibilities of
CLR

√ Garbage Collection :- CLR automatically manages memory thus eliminating
memory leaks. When objects are not referred GC automatically releases those
memories thus providing efficient memory management.

√ Code Access Security :- CAS grants rights to program depending on the security
configuration of the machine. Example the program has rights to edit or create
a new file but the security configuration of machine does not allow the program
to delete a file. CAS will take care that the code runs under the environment of
machines security configuration.

√ Code Verification :- This ensures proper code execution and type safety while
the code runs. It prevents the source code to perform illegal operation such as
accessing invalid memory locations etc.

√ IL( Intermediate language )-to-native translators and optimizer’s :- CLR uses
JIT and compiles the IL code to machine code and then executes. CLR also
determines depending on platform what is optimized way of running the IL
code.

-------------------------------------------------------------------------------------------------

(III) What is a CTS?

In order that two language communicate smoothly CLR has CTS (Common Type System).Example in VB you have “Integer” and in C++ you have “long” these datatypes are not compatible so the interfacing between them is very complicated. In order to able that two different languages can communicate Microsoft introduced Common Type System. So “Integer” datatype in VB6 and “int” datatype in C++ will convert it to System.int32 which is datatype of CTS. CLS which is covered in the coming question is subset of CTS.

-------------------------------------------------------------------------------------------------

(IV) What is a CLS(Common Language Specification)?

This is a subset of the CTS which all .NET languages are expected to support. It was always a
dream of Microsoft to unite all different languages in to one umbrella and CLS is one step
towards that. Microsoft has defined CLS which are nothing but guidelines that language to follow
so that it can communicate with other .NET languages in a seamless manner.

-------------------------------------------------------------------------------------------------

(V) What is a Managed Code?

Managed code runs inside the environment of CLR i.e. .NET runtime. In short all IL are managed code. But if you are using some third party software example VB6 or VC++ component they are unmanaged code as .NET runtime (CLR) does not have control over the source code execution of the language.

-------------------------------------------------------------------------------------------------

Google story Video

2009-11-27T12:49:00.001+05:30

GOOGLE HISTORY VIDEO

WITH REGARDS..

R.RAVI SANKAR

What Is the .NET Framework?

2009-11-03T08:42:00.002+05:30

What Is the .NET Framework ?

The .NET Framework is a new and revolutionary platform created by Microsoft for developing applications. The most interesting thing about this statement is how vague it is — but there are good reasons for this. For a start, note that it doesn ’ t “ develop applications on the Windows operating system. ” Although the Microsoft release of the .NET Framework runs on the Windows operating system, it is fast becoming possible to find alternative versions that will work on other systems. One example of this is Mono, an open - source version of the .NET Framework (including a C# compiler) that runs on several operating systems, including various flavors of Linux and Mac OS. More such projects are in the pipeline and may be available by the time you read this. In addition, you can use the Microsoft .NET Compact Framework (essentially a subset of the full .NET Framework) on personal digital assistant (PDA) class devices and even some smart phones. One of the key motivations behind the .NET Framework is its intended use as a means of integrating disparate operating systems.

In addition, the preceding definition of the .NET Framework includes no restriction on the type of applications that are possible. That ’ s because there is no restriction — the .NET Framework allows the creation of Windows applications, Web applications, Web services, and pretty much anything else you can think of.

The .NET Framework has been designed so that it can be used from any language, including C# (the subject of this book) as well as C++, Visual Basic, JScript, and even older languages such as COBOL. For this to work, .NET - specific versions of these languages have also appeared, and more are being released all the time. Not only do all of these have access to the .NET Framework, but they can also communicate with each other. It is perfectly possible for C# developers to make use of code written by Visual Basic programmers, and vice versa.

All of this provides a hitherto unthinkable level of versatility and is part of what makes using the .NET Framework such an attractive prospect.

Top 100 IT Companies (Rank-wise List)

2009-11-03T08:39:00.000+05:30

Top 100 IT Companies (Rank-wise List)

Rank

Company

100

101

Tata Consultancy Services (TCS)

Infosys Technologies Ltd

Wipro Limited

Hewlett-Packard India Pvt. Ltd

IBM India Limited

Satyam Computer Services Ltd.

HCL Technologies Ltd.

Intel Technology India Pvt. Ltd.

CISCO Systems India Pvt. Ltd.

Patni Computer Systems Ltd.

Cognizant Technology Solutions India

HCL Infosystems Ltd.

Mahindra-British Telecom

Redington (India) Limited

i-Flex Solutions Ltd.

Oracle India Pvt. Ltd.

Moser Baer India Ltd.

Microsoft Corporation (India) Pvt. Ltd.

NIIT Limited

TATA Infotech Ltd.

iGATE Global Solutions Ltd.

Ingram Micro India (P) Ltd

Sun Microsystems India Pvt Ltd

Polaris Software Lab Ltd.

Samsung India Electronics Ltd.

Perot Systems TSI (India) Limited

SAP India Pvt. Ltd.

American Power Conversion

Celetronix India Pvt. Ltd.

Computer Associates India Pvt. Ltd

Dell Computer India Pvt. Ltd.

Hexaware Technologies

Larsen & Toubro Infotech Ltd.

Siemens Information Systems Ltd.

Mastek Ltd.

CMS Computers Ltd.

Texas Instruments India Pvt. Ltd

Honeywell Technology Solutions Lab

Acer India (Pvt) Ltd.

MphasiS BFL Ltd.

Datacraft India Limited

Nortel Networks (I) Pvt Ltd

Syntel (India) Ltd.

Flextronics Software Systems Ltd

Kanbay Software India Pvt. Ltd.

Rolta India Ltd.

Infinite Computer Solutions (I) Pvt Ltd

GTL Limited

Covansys (I) Pvt. Ltd.

Sify Limited

Zensar Technologies Ltd.

Tulip IT Services Ltd

Zenith Computers Limited

Sonata Software Ltd

D-Link (India) Ltd.

Mascon Global Limited

3i Infotech Limited

WeP Peripherals Ltd.

Computer Sciences Corporation India

Philips Innovation Campus

Xansa India

Canon India Pvt. Ltd.

TVS Electronics Ltd.

Infotech Enterprises Ltd.

KPIT Cummins Infosystems Limited

ITC Infotech India

MindTree Consulting Pvt. Ltd.

PCS Technology Ltd.

Sasken Communication Technologies

Tally Solutions Pvt. Ltd.

Ramco Systems Ltd.

Epson India Pvt. Ltd.

Numeric Power Systems Ltd.

Rashi Peripherals Pvt. Ltd

Network Solutions Pvt. Ltd.

TATA Elxsi Ltd.

Aftek Infosys Limited

EMC Data Storage Systems India

Tata Technologies Ltd.

Geometric Software Solutions Co.

Cranes Software International Limited

Accel Frontline Limited

Mediaman Infotech Pvt. Ltd.

Priya Limited - IT Products Division

Keane India Ltd.

Persistent Systems Pvt. Ltd.

Aptech Limited

Lipi Data Systems Ltd.

Cadence Design Systems (India)

Intex Technologies (India) Ltd

Aditi Technologies Pvt Ltd

MRO-TEK Limited

Subex Systems Limited

Blue Star Infotech Limited

Aztec Software & Technology Services

Pentamedia Graphics Ltd.

TATA Interactive Systems

Birlasoft Limited

DB Power Electronics (P) Ltd

Atlanta IT Solutions Pvt. Ltd

RMSI Pvt. Ltd.

Feel free to Post your comments,...

With Regards,,

R. Ravi Sankar.

Basics in Computers

2009-10-30T08:11:00.001+05:30

1. What is the difference between interpreters and compilers?

Interpreters read through source code and translate a program, turning the

programmer's code, or program instructions, directly into actions. Compilers

translate source code into an executable program that can be run at a later time.

2. How do you compile the source code with your compiler?

Every compiler is different. Be sure to check the documentation that came with

your compiler.

3. What does the linker do?

The linker's job is to tie together your compiled code with the libraries supplied

by your compiler vendor and other sources. The linker lets you build your

program in pieces and then link together the pieces into one big program.

4. What are the steps in the development cycle?

Edit source code, compile, link, test, repeat.

Comment me for newer enhancements..

with regards..

R.Ravi Sankar.

Some Resemblences In C# and Java

2009-08-11T19:01:00.003+05:30

1. We Are All Objects

Just like Java, C# has a single rooted class hierarchy where all classes in C# are subclasses of System.Object the same way all Java classes are subclasses of java.lang.Object. The methods of the two languages' Object classes share some similarities (e.g. System.Object's ToString() to java.lang.Object's toString()) and differences (System.Object does not have analogs to wait(), notify() or notifyAll() in java.lang.Object).

NOTE: In C#, the object class can either be written as object or Object. The lower case "object" is a C# keyword which is replaced with the class name "System.Object" during compilation.

2. Keyword Jumble

There are a large number of syntactic similarities between Java and C#, similarly almost every Java keyword has a C# equivalent except for a few like transient, throws and strictfp. Below is a table of Java and C# keywords with the Java keywords in red while the equivalent C# keywords are in blue.

C# keyword

Java keyword

C# keyword

Java keyword

C# keyword

Java keyword

C#

keyword

Java

keyword

abstract

abstract

extern

native

operator

N/A

throw

throw

as

N/A

false

false

out

N/A

true

true

base

super

finally

finally

override

N/A

try

try

bool

boolean

fixed

N/A

params

...

typeof

N/A

break

break

float

float

partial

N/A

uint

N/A

byte

N/A

for

for

private

private

ulong

N/A

case

case

foreach

for

protected

N/A

unchecked

N/A

catch

catch

get

N/A

public

public

unsafe

N/A

char

char

goto

goto¹

readonly

N/A

ushort

N/A

checked

N/A

if

if

ref

N/A

using

import

class

class

implicit

N/A

return

return

value

N/A

const

const¹

in

N/A

sbyte

byte

virtual

N/A

continue

continue

int

int

sealed

final

void

void

decimal

N/A

interface

interface

set

N/A

volatile

volatile

default

default

internal

protected

short

short

where

extends

delegate

N/A

is

instanceof

sizeof

N/A

while

while

do

do

lock

synchronized

stackalloc

N/A

yield

N/A

double

double

long

long

static

static

:

extends

else

else

namespace

package

string

N/A

:

implements

enum

N/A

new

new

struct

N/A

N/A

strictfp

event

N/A

null

null

switch

switch

N/A

throws

explicit

N/A

object

N/A

this

this

N/A

transient²

NOTE: Although goto and const are Java language keywords they are unused in the Java language.

NOTE: The [NonSerialized] attribute in C# is equivalent to the transient keyword in Java.

3. Of Virtual Machines and Language Runtimes

Just like Java is typically compiled to Java byte code which then runs in managed execution environment (the Java Virtual Machine or JVM) so also is C# code compiled to an Intermediate Language (IL) which then runs in the Common Language Runtime (CLR). Both platforms support native compilation via Just In Time compilers.

NOTE: While the Java platform supports interpretation of byte code or byte code being JITed then run natively, the .NET platform only supports native execution of C# code because the IL code is always natively compiled before running.

4. Heap Based Classes and Garbage Collection

In Java objects are created on the heap using the new keyword. Most classes in C# are created on the heap by using the new keyword. Also just as the JVM manages the destruction of objects so also does the CLR via a Mark and Compact garbage collection algorithm

NOTE: C# also supports stack-based classes, called value types, which are discussed further below.

5. Arrays Can Be Jagged

In languages like C and C++, each subarray of a multidimensional array must have the same dimensions. In Java and C# arrays do not have to be uniform because jagged arrays can be created as one-dimensional arrays of arrays. In a jagged array the contents of the array are arrays which may hold instances of a type or references to other arrays. For this reason the rows and columns in a jagged array need not have uniform length as can be seen from the following code snippet:

The above code snippet is valid for both C# and Java.

6. No Global Methods

Just like Java and unlike C++, methods in C# have to be part of a class either as member or static methods.

7. Interfaces, Yes. Multiple Inheritance, No

C#, like Java, supports the concept of an interface which is akin to a pure abstract class. Similarly C# and Java both allow only single inheritance of classes but multiple inheritance (or implementation) of interfaces.

8. Strings Are Immutable

C# has a System.String class which is analogous to the java.lang.String class. Both classes are immutable meaning that the values of the strings cannot be changed once the strings have been created. In both instances methods that appear to modify the actual content of a string actually create a new string to return, leaving the original string unchanged. Thus the following C# and Java code does not modify the string in either case

C# Code

String csString = "Apple Jack";

csString.ToLower(); /* Does not modify string, instead returns lower case copy of string */

Java Code

String jString = "Grapes";

jString.toLowerCase(); /* Does not modify string, instead returns lower case copy of string */

To create a string-like object that allows modification in C# it is advisable to use the System.Text.StringBuilder class whereas in Java one would use the java.lang.StringBuffer class.

NOTE: In C#, the string class can either be written as string or String.

9. Unextendable Classes

Both Java and C# provide mechanisms to specify that a class should be the last one in an inheritance hierarchy and cannot be used as a base class. In Java this is done by preceding the class declaration with the final keyword while in C# this is done by preceding the class declaration with the sealed keyword. Below are examples of classes that cannot be extended in either language

C# Code

sealed class Student {

string fname;

string lname;

int uid;

void attendClass() {}

}

Java Code

final class Student {

String fname;

String lname;

int uid;

void attendClass() {}

}

10. Throwing and Catching Exceptions

Exceptions in C# and Java share a lot of similarities. Both languages support the use of the try block for indicating guarded regions, the catch block for handling thrown exceptions and the finally block for releasing resources before leaving the method. Both languages have an inheritance hierarchy where all exceptions are derived from a single Exception class. Exceptions can be caught and rethrown after some error handling occurs in both languages. Finally, both languages provide a mechanism for wrapping exceptions in one another for cases where a different exception is rethrown from the one that was caught. An example of using the exception wrapping capability is a three tier application where a SQLException is thrown during database access but is caught, examined, then an application specific exception is thrown. In this scenario the application specific exception can be initialized with the original SQLException so handlers of the application specific exception can access the original exception thrown if needed. Below are two equivalent code samples that show the similarities between exceptions in both languages.

NOTE: Although exceptions in both languages support methods for getting a stack trace, only Java exceptions have methods that allow one to alter the stack trace.

C# Code

using System;

using System.IO;

class MyException: Exception{

public MyException(string message): base(message){ }

public MyException(string message, Exception innerException):

base(message, innerException){ }

}

public class ExceptionTest {

static void DoStuff(){

throw new FileNotFoundException();

}

public static void Main(string[] args){

try{

try{

DoStuff();

return; //won't get to execute

}catch(IOException ioe){ /* parent of FileNotFoundException */

throw new MyException("MyException occured", ioe); /* rethrow new exception with inner exception specified */

}

}finally{

Console.WriteLine("***Finally block executes even though MyException not caught***");

}

}//Main(string[])

} // ExceptionTest

Java Code

class MyException extends Exception{

public MyException(String message){ super(message); }

public MyException(String message, Exception innerException){ super(message, innerException); }

}

public class ExceptionTest {

static void doStuff(){

throw new ArithmeticException();

}

public static void main(String[] args) throws Exception{

try{

try{

doStuff();

return; //won't get to execute

}catch(RuntimeException re){ /* parent of ArithmeticException */

throw new MyException("MyException occured", re); /* rethrow new exception with cause specified */

}

}finally{

System.out.println("***Finally block executes even though MyException not caught***");

}

}//main(string[])

} // ExceptionTest

Further Queries comment me..

With Regards..
R.Ravi Sankar.

Database Connectivity In C# using OLE DB

2009-08-10T18:54:00.003+05:30

using System;
using System.Collections.Generic;
using System.Text;
using System.Data;
using System.Data.OleDb;
namespace ConsoleApplication15
{
class Program
{
static void Main(string[] args)
{
//create the database connection
OleDbConnection aConnection = new OleDbConnection("Provider=Microsoft.Jet.OLEDB.4.0;Data Source=g:\\project.mdb");

//create the command object and store the sql query
OleDbCommand aCommand = new OleDbCommand("select * from book", aConnection);
try
{
aConnection.Open();

//create the datareader object to connect to table
OleDbDataReader aReader = aCommand.ExecuteReader();
Console.WriteLine("This is the returned data from book table");
Console.WriteLine("\n B_id\t\t Title\t\t Auther\t\t No_of_page\t\tNo_of_piece\n");

//Iterate throuth the database
while (aReader.Read())
{
Console.WriteLine("\n"+ aReader.GetInt32(0).ToString()+"\t\t"+ aReader.GetString(1).ToString()+"\t\t"+aReader.GetString(2).ToString()+"\t\t" + aReader.GetInt32(3).ToString()+"\t\t"+ aReader.GetInt32(4).ToString());

}

//close the reader
aReader.Close();

//close the connection Its important.
aConnection.Close();
}

//Some usual exception handling
catch (OleDbException e)
{
Console.WriteLine("Error: {0}", e.Errors[0].Message);
}
Console.ReadLine();
}
}
}

Further queries comment me..

With Regards,

R.Ravi Sankar.

Dot NET Meta Data

2009-08-09T12:28:00.003+05:30

.NET metadata, in the Microsoft .NET framework, refers to certain data structures embedded within the Common Intermediate Language code that describes the high-level structure of the code. Metadata describes all classes and class members that are defined in the assembly, and the classes and class members that the current assembly will call from another assembly. The metadata for a method contains the complete description of the method, including the class (and the assembly that contains the class), the return type and all of the method parameters.

A .NET language compiler will generate the metadata and store this in the assembly containing the CIL. When the CLR executes CIL it will check to make sure that the metadata of the called method is the same as the metadata that is stored in the calling method. This ensures that a method can only be called with exactly the right number of parameters and exactly the right parameter types.

ATTRIBUTRES

Developers can add metadata to their code through attributes. There are two types of attributes, custom and pseudo custom attributes, and to the developer these have the same syntax. Attributes in code are messages to the compiler to generate metadata. In CIL, metadata such as inheritance modifiers, scope modifiers, and almost anything that isn't either opcodes or streams, are also referred to as attributes.

A custom attribute is a regular class that inherits from the Attribute class. A custom attribute can be used on any method, property, class or entire assembly with the syntax:[AttributeName(optional parameter, optional name=value pairs)] as in:

 [Custom]
 [Custom(1)]
 [Custom(1, comment="yes")]

Custom attributes are used by the .NET Framework extensively. Windows Communication Framework uses attributes to define service contracts, ASP.NET uses these to expose methods as web services, LINQ to SQL uses them to define the mapping of classes to the underlying relational schema, Visual Studio uses them to group together properties of an object, the class developer indicates the category for the object's class by applying the [Category] custom attribute. Custom attributes are interpreted by application code and not the CLR.When the compiler sees a custom attribute it will generate custom metadata that is not recognised by the CLR. The developer has to provide code to read the metadata and act on it. As an example, the attribute shown in the example can be handled by the code:

class CustomAttribute : Attribute
{   private int paramNumber = 0;
   private string comment = "";
 
   public CustomAttribute() { }
   public CustomAttribute(int num) { paramNumber = num; }
 
   public String Comment
   {
      set { comment = value; }
   }
}

The name of the class is mapped to the attribute name. The Visual C# compiler automatically adds the string "Attribute" at the end of any attribute name. Consequently every attribute class name should end with this string, but it is legal to define an attribute without the Attribute-suffix. When affixing an attribute to an item, the compiler will look for both the literal name and the name with Attribute added to the end, i.e. if you were to write [Custom] the compiler would look for both Custom and CustomAttribute. If both exist, the compiler fails. The attribute can be prefixed with "@" if you don't want to risk ambiguity, so writing [@Custom] will not match CustomAttribute. Using the attribute invokes the constructor of the class. Overloaded constructors are supported. Name-Value pairs are mapped to properties, the name denotes the name of the property and the value supplied is set by the property.

Sometimes there is ambiguity concerning to what you are affixing the attribute. Consider the following code:

[Orange]
public int ExampleMethod(string input){    //method body goes here
}

What has been marked as orange? Is it the ExampleMethod, its return value, or perhaps the entire assembly? In this case, the compiler will default, and treat the attribute as being affixed to the method. If this is not what was intended, or if the author wishes to clarify their code, an attribute target may be specified. Writing [return: Orange] will mark the return value as orange,[assembly: Orange] will mark the entire assembly. The valid targets are assembly, field, event, method, module, param, property, return and type.

A pseudo-custom attribute is used just like regular custom attributes but they do not have a custom handler; rather the compiler has intrinsic awareness of the attributes and handles the code marked with such attributes differently. Attributes such as Serializable and Obsolete are implemented as pseudo-custom attributes. Pseudo-custom attributes should never be used by ILASM, as it has adequate syntax to describe the metadata.

META STORAGE

Assemblies contain tables of metadata. These tables are described by the CIL specification. The metadata tables will have zero or more entries and the position of an entry determines its index. When CIL code uses metadata it does so through a metadata token. This is a 32-bit value where the top 8 bits identify the appropriate metadata table, and the remaining 24 bits give the index of the metadata in the table. The Framework SDK contains a sample called metainfo that will list the metadata tables in an assembly, however, this information is rarely of use to a developer. Metadata in an assembly may be viewed using the ILDASM tool provided by the .NET Framework SDK.

REFLECTION

Reflection is the API used to read .NET metadata. The reflection API provides a logical view of metadata rather than the literal view provided by tools like metainfo. Reflection in version 1.1 of the .NET framework can be used to inspect the descriptions of classes and their members, and invoke methods. However, it does not allow runtime access to the CIL for a method. Version 2.0 of the framework allows the CIL for a method to be obtained.

Further queries comment me.

With Regards,

R.Ravi Sankar.

Common Language Runtime in Dot Net Framework

2009-08-09T12:22:00.003+05:30

The Common Language Runtime (CLR) is a core component of Microsoft's .NET initiative. It is Microsoft's implementation of the Common Language Infrastructure (CLI) standard, which defines an execution environment for program code. The CLR runs a form of bytecode called theCommon Intermediate Language (CIL, previously known as MSIL -- Microsoft Intermediate Language).

Developers using the CLR write code in a language such as C# or VB.NET. At compile time, a .NET compiler converts such code into CIL code. At runtime, the CLR's just-in-time compilerconverts the CIL code into code native to the operating system. Alternatively, the CIL code can be compiled to native code in a separate step prior to runtime. This speeds up all later runs of the software as the CIL-to-native compilation is no longer necessary.

Although some other implementations of the Common Language Infrastructure run on non-Windows operating systems, Microsoft's implementation runs only on Microsoft Windows operating systems.

The CLR allows programmers to ignore many details of the specific CPU that will execute the program. It also provides other important services, including the following:

CLR ARCHITECTURE

Further quries comment me.

With Regards,

R.Ravi Sankar.

C# keyword	Java keyword	C# keyword	Java keyword	C# keyword	Java keyword	C# keyword	Java keyword
abstract	abstract	extern	native	operator	N/A	throw	throw
as	N/A	false	false	out	N/A	true	true
base	super	finally	finally	override	N/A	try	try
bool	boolean	fixed	N/A	params	...	typeof	N/A
break	break	float	float	partial	N/A	uint	N/A
byte	N/A	for	for	private	private	ulong	N/A
case	case	foreach	for	protected	N/A	unchecked	N/A
catch	catch	get	N/A	public	public	unsafe	N/A
char	char	goto	goto¹	readonly	N/A	ushort	N/A
checked	N/A	if	if	ref	N/A	using	import
class	class	implicit	N/A	return	return	value	N/A
const	const¹	in	N/A	sbyte	byte	virtual	N/A
continue	continue	int	int	sealed	final	void	void
decimal	N/A	interface	interface	set	N/A	volatile	volatile
default	default	internal	protected	short	short	where	extends
delegate	N/A	is	instanceof	sizeof	N/A	while	while
do	do	lock	synchronized	stackalloc	N/A	yield	N/A
double	double	long	long	static	static	:	extends
else	else	namespace	package	string	N/A	:	implements
enum	N/A	new	new	struct	N/A	N/A	strictfp
event	N/A	null	null	switch	switch	N/A	throws
explicit	N/A	object	N/A	this	this	N/A	transient²