.NET Interview 1

What is a IL?

(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.

What are the responsibilities of 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.

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.

What is a CLS(Common Language Specification)?

This is a subset of the CTS which all .NET languages are expected to support. 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.It 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.

What are the 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 many times its possible that programmers will use the same class name.By qualifying NameSpace with classname this collision is able to be removed.

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.

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 an 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 their individual folders.

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.

What is the concept of strong names ?

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.

How to add and remove an assembly from GAC?

There are two ways to install .NET assembly in GAC:

Using Microsoft Installer Package. You can get download of installer from http://www.microsoft.com.

Using Gacutil. Goto “Visual Studio Command Prompt” and type “gacutil –i (assembly_name)”, where (assembly_name) is the DLL name of the project.

What is Delay signing ?

During development process you will need strong name keys to be exposed to developer which 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 an 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. CLR automatically releases objects when they are no longer in use and refernced. 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 are different types of JIT ?

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 which 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 a process in which object instances are created and copy values 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 is the difference between Convert.toString and .toString() method ?

Just to give an understanding of what the above question means seethe below code.

int i =0;

MessageBox.Show(i.ToString());

MessageBox.Show(Convert.ToString(i));

We can convert the integer “i” using “i.ToString()” or “Convert.ToString” so what’s the difference.

The basic difference between them is “Convert” function handles NULLS while “i.ToString()” does not it will throw a NULL reference exception error. So as good coding practice using “convert” is always safe.

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