.Net Framework Interview Questions
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.
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 leakes. When objects are not referred GC automatically releases those
memory 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.
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 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.
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.
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.
What is a Assembly ?
√ Assembly is unit of deployment like EXE or a DLL.
√ An assembly consists of one or more files (dlls, exe’s, 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 assembly is completely self-describing.An assembly contains metadata
information, which is used by the CLR for everything from type checking and
security to actually invoking the components methods.As all information is in
assembly itself it is independent of registry.This is the basic advantage as
compared to COM where the version was stored in registry.
√ Multiple versions can be deployed side by side in different folders. These
different versions can execute at the same time without interfering with each
other.Assemblies can be private or shared. For private assembly deployment,the
assembly is copied to the same directory as the client program that references
it.No registration is needed, and no fancy installation program is required.
When the component is removed, no registry cleanup is needed,and no uninstall
program is required. Just delete it from the hard drive.
√ In shared assembly deployment, an assembly is installed in the Global Assembly
Cache (or GAC). The GAC contains shared assemblies that are
globally accessible to all .NET applications on the machine.
What are different types of Assembly?
There are two types of assembly Private and Public assembly.A private assembly is normally used
by a single application, and is stored in the application's directory, or a sub-directory 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. Crystal report classes which will be used by all application for
Reports..
What is NameSpace?
Namespace has two basic functionality :-
√ NameSpace Logically group types.Example System.Web.UI logically groups
our UI related features.
√ In Object Oriented world may times its possible that programmers will use the
same class name.By qualifying NameSpace with classname this collision can
be removed.
(B) What is Difference between NameSpace and Assembly?
Following are the differences between namespace and assembly :
√ Assembly is physical grouping of logical units. Namespace logically groups
classes.
√ Namespace can span multiple assembly.
If you want to view a Assembly how to you go about it ?
Twist : What is ILDASM ?
When it comes to understanding of internals nothing can beat ILDASM.ILDASM basically converts
the whole exe or dll in to IL code.To run ILDASM you have to go to "C:\Program Files\Microsoft
Visual Studio .NET 2003\SDK\v1.1\Bin". Note that i had v1.1 you have to probably change it
depending on the type of framework version you have.
If you run IDASM.EXE from the path you will be popped with the IDASM exe program as
shown in figure ILDASM.Click on file and browse to the respective directory for the DLL whose
assembly you want to view.After you select the DLL you will be popped with a tree view details
of the DLL as shown in figure ILDASM.On double clicking on manifest you will be able to view
details of assembly , internal IL code etc as shown in Figure Manifest View.
What is Manifest?
Assembly metadata is stored in Manifest.Manifest contains all the metadata needed to do the
following things( See Figure Manifest View for more details) :
√ Version of assembly
√ Security identity
√ Scope of the assembly
√ resolve references to resources and classes.
√ The assembly manifest can be stored in either a PE file (an .exe or .dll) with
Microsoft intermediate language (MSIL) code or in a stand-alone PE file that
contains only assembly manifest information.
Where is version information stored of a assembly ?
Version information is stored in assembly in manifest.
Is versioning applicable to private assemblies?
Versioning concept is only applicable to global assembly cache (GAC) as private assembly lie in
there individual folders.
What is GAC ?
Twist :- What are situations when you register .NET assembly in GAC ?
GAC (Global Assembly Cache) is used where shared .NET assembly reside.GAC is used in the
following situations :-
√ If the application has to be shared among several application.
√ If the assembly has some special security requirements like only administrators
can remove the assembly.If the assembly is private then a simple delete of
assembly the assembly file will remove the assembly.
Note :- Registering .NET assembly in GAC can lead to the old problem of DLL hell.
Where COM version was stored in central registry.So GAC should be used when
absolutely necessary.
What is concept of strong names ?
Twist :- How do we generate strong names or what is the process of generating strong names
What is use of SN.EXE , How do we apply strong names to assembly ? , How do you
sign an assembly ?
Strong name is similar to GUID(It is supposed to be unique in space and time) in COM
components.Strong Name is only needed when we need to deploy assembly in GAC.Strong
Names helps GAC to differentiate between two versions.Strong names use public key cryptography
(PKC) to ensure that no one can spoof it.PKC use public key and private key concept.
Following are the step to generate a strong name and sign a assembly :-
Go to “Visual Studio Command Prompt”.See below figure to “Visual studio
Command Prompt”.Note the samples are compiled in 2005 but 2003 users do
not have to worry about it.Same type of command prompt will be seen in
2003 also.
After you are in command prompt type sn.exe -k “c:\test.snk”.
What is Delay signing ?
During development process you will need strong name keys to be exposed to developer which
will is not a good practice from security aspect point of view.In such situations you can assign the
key later on and during development you an use delay signing
Following is process to delay sign a assembly:
√ First obtain your string name keys using SN.EXE.
√ Annotate the source code for the assembly with two custom attributes from
System.Reflection: AssemblyKeyFileAttribute, which passes the name of the file
containing the public key as a parameter to its constructor. AssemblyDelaySignAttribute,
which indicates that delay signing is being used by passing true as a parameter to its
constructor. For example as shown below:
[Visual Basic]
<Assembly:AssemblyKeyFileAttribute("myKey.snk")>
<Assembly:AssemblyDelaySignAttribute(true)>
[C#]
[assembly:AssemblyKeyFileAttribute("myKey.snk")]
[assembly:AssemblyDelaySignAttribute(true)]
The compiler inserts the public key into the assembly manifest and reserves space in the PE file for
the full strong name signature. The real public key must be stored while the assembly is built so
that other assemblies that reference this assembly can obtain the key to store in their own assembly
reference.
√ Because the assembly does not have a valid strong name signature, the verification of
that signature must be turned off. You can do this by using the –Vr option with the
Strong Name tool.The following example turns off verification for an assembly called
myAssembly.dll.
Sn –Vr myAssembly.dll
Just before shipping, you submit the assembly to your organization's signing authority
for the actual strong name signing using the –R option with the Strong Name tool.The
following example signs an assembly called myAssembly.dll with a strong name using
the sgKey.snk key pair.
Sn -R myAssembly.dll sgKey.snk
What is garbage collection?
Garbage collection is a CLR feature which automatically manages memory. Programmers forget
to release the objects while coding ..... laziness ( Remember in VB6 where one of the good
practices is to set object to nothing).CLR automatically releases objects when they are no longer
referenced and in use.CLR runs on non-deterministic to see the unused objects and cleans them.
One side effect of this non-deterministic feature is that we cannot assume an object is destroyed
when it goes out of the scope of a function. Therefore, we should not put code into a class
destructor to release resources.
Can we force garbage collector to run ?
System.GC.Collect() forces garbage collector to run.This is not recommended but can be used if
situations arises.
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.
Using reflection you can also dynamically invoke methods using System.Type.Invokemember.Below
is sample source code if needed you can also get this code from CD provided , go to “Source
code” folder in “Reflection Sample” folder.
Public Class Form1
Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As
System.EventArgs) Handles MyBase.Load
Dim Pobjtype As Type
Dim PobjObject As Object
Dim PobjButtons As New Windows.Forms.Button()
Pobjtype = PobjButtons.GetType()
For Each PobjObject In Pobjtype.GetMembers
LstDisplay.Items.Add(PobjObject.ToString())
Next
End Sub
End Class
Sample source code uses reflection to browse through “Button” class of “Windows.Forms”.If
you compile and run the program following is output as shown in “Sample Reflection Display”.Using
reflection you can also dynamically invoke a method using “System.Type.InvokeMember”.
What are different type of JIT ?
Note :- This question can only be asked when the interviewer does not know what he
wants.It was asked to me in one of interview and for 15 minutes he was roaming around
the same question in order to get answer from me (requirement was for a simple database
project). Beware of such companies and interviewers you can land up no where.
JIT compiler is a part of the runtime execution environment.
In Microsoft .NET there are three types of JIT compilers:
Pre-JIT. Pre-JIT compiles complete source code into native code in a single compilation
cycle. This is done at the time of deployment of the application.
√ Econo-JIT. Econo-JIT compiles only those methods that are called at runtime.
However, these compiled methods are removed when they are not required.
√ Normal-JIT. Normal-JIT compiles only those methods that are called at runtime.
These methods are compiled the first time they are called, and then they are stored in
cache. When the same methods are called again, the compiled code from cache is
used for execution.
What are Value types and Reference types ?
Value types directly contain their data are either allocated on the stack or allocated in-line in a
structure.
Reference types store a reference to the value's memory address, and are allocated on the heap.
Reference types can be self-describing types, pointer types, or interface types.
Variables that are value types each have their own copy of the data, and therefore operations on
one variable do not affect other variables. Variables that are reference types can refer to the same
object; therefore, operations on one variable can affect the same object referred to by another
variable.All types derive from the System.Object base type.
What is concept of Boxing and Unboxing?
Boxing permits any value type to be implicitly converted to type object or to any interface type
implemented by value type.Boxing is process in which a object instances created and copying
value types value in to that instance.
Unboxing is vice versa of boxing operation where the value is copied from the instance in to
appropriate storage location.
Below is sample code of boxing and unboxing where integer data type is converted in to object
and then vice versa.
Dim x As Integer
Dim y As Object
x = 10
‘ boxing process
y = x
‘ unboxing process
x = y
What’s difference between VB.NET and C# ?
Well this is the most debatable issue in .NET community and people treat there languages like
religion.Its a subjective matter which language is best.Some like VB.NET’s natural style and some
like professional and terse C# syntaxes.Both use the same framework and speed is also very much
equivalents . But still lets list down some major differences between them :-
Advantages VB.NET :-
√ Has support for optional parameters which makes COM interoperability much easy.
√ With Option Strict off late binding is supported.Legacy VB functionalities can be
used by using Microsoft.VisualBasic namespace.
√ Has the WITH construct which is not in C#.
√ The VB.NET part of Visual Studio .NET compiles your code in the background.
While this is considered an advantage for small projects, people creating very large
projects have found that the IDE slows down considerably as the project gets larger.
Advantages of C#
√ XML documentation is generated from source code but this is now been incorporated
in Whidbey.
√ Operator overloading which is not in current VB.NET but is been introduced in
Whidbey.
√ The using statement, which makes unmanaged resource disposal simple.
√ Access to Unsafe code. This allows pointer arithmetic etc, and can improve
performance in some situations. However, it is not to be used lightly, as a lot of the
normal safety of C# is lost (as the name implies).This is the major difference that you
can access unmanaged code in C# and not in VB.NET.
What’s difference between System exceptions and Application
exceptions?
All exception derives from Exception Base class. Exceptions can be generated programmatically
or can be generated by system. Application Exception serves as the base class for all application
specific exception classes. It derives from Exception but does not provide any extended functionality.
You should derive your custom application exceptions from Application Exception.
Application exception are used when we want to define user defined exception. While system
exception are all which are defined by .NET.
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 a application to read but
now write and delete rights are given to the application.
What is a satellite assembly?
In multilingual application in .NET to support multilingual functionality you can have modules
which are customized for localization.These assemblies are called as satellite assemblies. You can
distribute these assemblies separately than the core modules.
