.net interview questions

.NET Framework Interview questions

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

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.net interview questions

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.net interview questions

What is an application server?

As defined in Wikipedia, an application server is a software engine that delivers applications to client computers or devices. The application server runs your server code. Some well known application servers are IIS (Microsoft), WebLogic Server (BEA), JBoss (Red Hat), WebSphere (IBM).

Compare C# and VB.NET

A detailed comparison can be found over here.

What is a base class and derived class?

A class is a template for creating an object. The class from which other classes derive fundamental functionality is called a base class. For e.g. If Class Y derives from Class X, then Class X is a base class.

The class which derives functionality from a base class is called a derived class. If Class Y derives from Class X, then Class Y is a derived class.

What is an extender class?

An extender class allows you to extend the functionality of an existing control. It is used in Windows forms applications to add properties to controls.

A demonstration of extender classes can be found over here.

What is inheritance?

Inheritance represents the relationship between two classes where one type derives functionality from a second type and then extends it by adding new methods, properties, events, fields and constants.

C# support two types of inheritance:

  • Implementation inheritance
  • Interface inheritance

What is implementation and interface inheritance?

When a class (type) is derived from another class(type) such that it inherits all the members of the base type it is Implementation Inheritance.

When a type (class or a struct) inherits only the signatures of the functions from another type it is Interface Inheritance.

In general Classes can be derived from another class, hence support Implementation inheritance. At the same time Classes can also be derived from one or more interfaces. Hence they support Interface inheritance.

Source: Exforsys.

What is inheritance hierarchy?

The class which derives functionality from a base class is called a derived class. A derived class can also act as a base class for another class. Thus it is possible to create a tree-like structure that illustrates the relationship between all related classes. This structure is known as the inheritance hierarchy.

How do you prevent a class from being inherited?

In VB.NET you use the NotInheritable modifier to prevent programmers from using the class as a base class. In C#, use the sealed keyword.

When should you use inheritance?

Read this.

Define Overriding?

Overriding is a concept where a method in a derived class uses the same name, return type, and arguments as a method in its base class. In other words, if the derived class contains its own implementation of the method rather than using the method in the base class, the process is called overriding.

Can you use multiple inheritance in .NET?

.NET supports only single inheritance. However the purpose is accomplished using multiple interfaces.

Why don’t we have multiple inheritance in .NET?

There are several reasons for this. In simple words, the efforts are more, benefits are less. Different languages have different implementation requirements of multiple inheritance. So in order to implement multiple inheritance, we need to study the implementation aspects of all the languages that are CLR compliant and then implement a common methodology of implementing it. This is too much of efforts. Moreover multiple interface inheritance very much covers the benefits that multiple inheritance has.

What is an Interface?

An interface is a standard or contract that contains only the signatures of methods or events. The implementation is done in the class that inherits from this interface. Interfaces are primarily used to set a common standard or contract.

When should you use abstract class vs interface or What is the difference between an abstract class and interface?

I would suggest you to read this. There is a good comparison given over here.

What are events and delegates?

An event is a message sent by a control to notify the occurrence of an action. However it is not known which object receives the event. For this reason, .NET provides a special type called Delegate which acts as an intermediary between the sender object and receiver object.

What is business logic?

It is the functionality which handles the exchange of information between database and a user interface.

What is a component?

Component is a group of logically related classes and methods. A component is a class that implements the IComponent interface or uses a class that implements IComponent interface.

What is a control?

A control is a component that provides user-interface (UI) capabilities.

What are the differences between a control and a component?

The differences can be studied over here.

What are design patterns?

Design patterns are common solutions to common design problems.

What is a connection pool?

A connection pool is a ‘collection of connections’ which are shared between the clients requesting one. Once the connection is closed, it returns back to the pool. This allows the connections to be reused.

What is a flat file?

A flat file is the name given to text, which can be read or written only sequentially.

What are functional and non-functional requirements?

Functional requirements defines the behavior of a system whereas non-functional requirements specify how the system should behave; in other words they specify the quality requirements and judge the behavior of a system.

E.g.

Functional – Display a chart which shows the maximum number of products sold in a region.

Non-functional – The data presented in the chart must be updated every 5 minutes.

What is the global assembly cache (GAC)?

GAC is a machine-wide cache of assemblies that allows .NET applications to share libraries. GAC solves some of the problems associated with dll’s (DLL Hell).

What is a stack? What is a heap? Give the differences between the two?

Stack is a place in the memory where value types are stored. Heap is a place in the memory where the reference types are stored.

Check this link for the differences.

What is instrumentation?

It is the ability to monitor an application so that information about the application’s progress, performance and status can be captured and reported.

What is code review?

The process of  examining the source code generally through a peer, to verify it against best practices.

What is logging?

Logging is the process of persisting information about the status of an application.

What are mock-ups?

Mock-ups are a set of designs in the form of screens, diagrams, snapshots etc., that helps verify the design and acquire feedback about the application’s requirements and use cases, at an early stage of the design process.

What is a Form?

A form is a representation of any window displayed in your application. Form can be used to create standard, borderless, floating, modal windows.

What is a multiple-document interface(MDI)?

A user interface container that enables a user to work with more than one document at a time. E.g. Microsoft Excel.

What is a single-document interface (SDI) ?

A user interface that is created to manage graphical user interfaces and controls into single windows. E.g. Microsoft Word

What is BLOB ?

A BLOB (binary large object) is a large item such as an image or an exe  represented in binary form.

What is ClickOnce?

ClickOnce is a new deployment technology that allows you to create and publish self-updating applications that can be installed and run with minimal user interaction.

What is object role modeling (ORM) ?

It is a logical model for designing and querying database models. There are various ORM tools in the market like CaseTalk, Microsoft Visio for Enterprise Architects, Infagon etc.

What is a private assembly?

A private assembly is local to the installation directory of an application and is used only by that application.

What is a shared assembly?

A shared assembly is kept in the global assembly cache (GAC) and can be used by one or more applications on a machine.

What is the difference between user and custom controls?

User controls are easier to create whereas custom controls require extra effort.

User controls are used when the layout is static whereas custom controls are used in dynamic layouts.

A user control cannot be added to the toolbox whereas a custom control can be.

A separate copy of a user control is required in every application that uses it whereas since custom controls are stored in the GAC, only a single copy can be used by all applications.

Where do custom controls reside?

In the global assembly cache (GAC).

What is a third-party control ?

A third-party control is one that is not created by the owners of a project. They are usually used to save time and resources and reuse the functionality developed by others (third-party).

What is a binary formatter?

Binary formatter is used to serialize and deserialize an object in binary format.

What is Boxing/Unboxing?

Boxing is used to convert value types to object.

E.g. int x = 1;

object obj = x ;

Unboxing is used to convert the object back to the value type.

E.g. int y = (int)obj;

Boxing/unboxing is quiet an expensive operation.

What is a COM Callable Wrapper (CCW)?

CCW is a wrapper created by the common language runtime(CLR) that enables COM components to access .NET objects.

What is a Runtime Callable Wrapper (RCW)?

RCW is a wrapper created by the common language runtime(CLR) to enable .NET components to call COM components.

What is a digital signature?

A digital signature is an electronic signature used to verify/gurantee the identity of the individual who is sending the message.

What is garbage collection?

Garbage collection is the process of managing the allocation and release of memory in your applications. Read this article for more information.

What is globalization?

Globalization is the process of customizing applications that support multiple cultures and regions.

What is localization?

Localization is the process of customizing applications that support a given culture and regions.

What is MIME?

The definition of MIME or Multipurpose Internet Mail Extensions as stated in MSDN is “MIME is a standard that can be used to include content of various types in a single message. MIME extends the Simple Mail Transfer Protocol (SMTP) format of mail messages to include multiple content, both textual and non-textual. Parts of the message may be images, audio, or text in different character sets. The MIME standard derives from RFCs such as 2821 and 2822”. Quoted from here.

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