ASP.NET & C# Interview Ques Ans for Exp.

Q) Generic syntax

Q) Features of C#

Q) validation controls in ASP.Net

Q) How to apply remoting?

DotNet remoting provides an abstract approach to interprocess communication that separates the remotable object from a specific client or server application domain and from a specific mechanism of communication. There are two ways:

1) Either add serializable attribute to the class OR

2) Inherit the class from MarshalByRefObject

Q) Cookies

Cookie is a solution in situations where we want to remember some data for a particular page and for a specific user so that same data can be used in other pages requested by the same user.

1) One of the important State management technique which is a Name-Value pair which on behalf of server saved in client machine (either in memory or file).

2) Once saved, browser automatically includes this name value pair along with every request it submits to that server.

3) Cookies are used for sharing data across web forms requested by same user/client.

4) Common Examples of Cookies

a) Authenticated user information

b) User specific settings on the site

c) Shopping cart

We want to use some information again and again such as selection of items by a user in shopping cart site, we can use cookies.

5) Cookies generated on server (added to the response) are added to the browser through a HTTP Response Header called “Set-Cookie”.

Set-Cookie:name=VALUE;expires:DATE;path:PATH;domain:DOMAIN_NAME;secure=IsHTTPS. These attributes are used by browser for deciding whether to include the cookie in the request or not (based on the URL of the request).

6) With every request the browser automatically includes all the cookies appropriate to that request. The Cookie Name- value pairs are submitted in the form of HTTP Request Header called “Cookie” and they are saved on the server in the form of CGI environmental variable(Server Variable) called as HTTP_COOKIE.

Cookie: N1=v1, N2=v2, N3=v3.

Note: Domain, path, expires, and secure attributes are not included with a cookie in the request. but these values are compared while sending response. For example if the Url is like www.microsoft.com

Types of Cookies:

1) Persistent cookies: A cookie which is permanently saved in a file. For example, these type of cookies can be shared among all the instances of IE but not to firefox. 2) Non-persistent cookie: These cookies are temporarily saved in the browser’s temporary memory not in file. These are not shared across browser instance and are also called as Session Cookie. For example every instance of IE will have different set of Non-Persistent Cookies.

Programming Cookies:

1) Request.Cookies is a collection of HttpCookie objects constructed for every cookie included in the request.

2) Response.Cookies is a collection of HttpCookie objects created for every cookie to be included in the response so that these cookies can be appended to the existing list of cookies on the client machine.

Default values for the properties of Cookie

1) value=””

2) path=”/”

3) Expires=(if not set then it’s a non-persistent cookie)

4) Domain=”Current domain of the website”

5) Secure=false

Limitations of Cookies:

1) 300 total cookies

2) 4 kilobytes per cookie (max size of cookie)

3) 20 cookies per server or domain

Q) What are Extension Methods?

Extension methods are static methods which allow you to easily extend a type, such as an integer or string, without re-compiling or modifying the type. Extension methods are available from 3.5 version of .Net framework.

One downside: An extension method is only called when there is no native method found. For example, assume that you created a method by name “GetFirstThreeCharacters(this String str)” on type String, but this method already exists in System.String then native method will be preferred over the extension.

How To Create and Extension Method?

1) Create a public static class (module in VB)

2) Define functions that you wish to perform and Make the functions as static.

3) Add “this” keyword to the first parameter of the extension method (in C#).

Note: The first parameter specifies which type the method operates on. “this” keyword basically tells the CLR that when this extension method is called, to use "this" parameter as the source.

public static class MyExtensions

{

public static int GetNumberOfCharacters(this String str)

{

return str.Length();

}

How to use in other projects?

Copy the namespace alongwith you project and use “Using <namespace>” in your project and start using the extension methods.

Q) What is COM?

Microsoft COM (Component Object Model) technology in the Microsoft Windows-family of Operating Systems enables software components to communicate. COM is used by developers to create reusable software components, link components together to build applications, and take advantage of Windows services. COM objects can be created with a variety of programming languages. Object-oriented languages, such as C++, provide programming mechanisms that simplify the implementation of COM objects. The family of COM technologies includes COM+, Distributed COM (DCOM) and ActiveX® Controls.

Q) Difference between & and && and also difference between | and ||?

& and &&, both are ‘AND’ operator but basic difference between is in the way they are executed. For both, syntax is same:

bool_exp1 && bool_exp2

bool_exp1 & bool_exp2

&&: In the first statement, first bool_exp1 will be executed and then the result of this expression decides the execution of the other statement. If it is false then the AND will be false so it makes no sense to execute the other statement. The bool_exp2 statement is executed if and only if bool_exp1 returns true on execution.

&: Now in the case of & things are different. The compiler will execute both statements and then the result will be ANDed. It’s an inefficient way of doing things because it makes no sense to execute the other statement if one is false because the result of AND is effective only for ANDing results evaluated to “true” and it’s possible when both statements are true.

||: It’s the same as above, in the case of “||” only one statement is executed and if it returns “true” then the other statement will not be executed. But if the first is false then the other will be checked for the value “true”. The reason for this is the way the “or” operator works. The “Or” operator depends on only one true, in other words if any of the expressions are true then the result will be true.

|: That’s OK but the way “|” behaves is the same as that of “&”, in other words both statements are executed regardless of the result of one statement. Check the following example and it will be clear.

CONCLUSION: Use && and || instead of & and |.

Q) How to get system(local i.e windows) user id and password?

system.environment.getenvironmentvariable( username )

Q) Difference between Finalise() and Dispose() methods?

Finalise	Dispose
Used to free unmanaged resources like files, database connections, COM etc. held by an object before that object is destroyed.	It is used to free unmanaged resources like files, database connections, COM etc. at any time.
Internally, it is called by Garbage Collector and cannot be called by user code.	Explicitly, it is called by user code and the class implementing dispose method must implement IDisposable interface.
It belongs to Object class.	It belongs to IDisposable Interface.
Implement it when you have unmanaged resources in your code, and want to make sure that these resources are freed when the Garbage collection happens.	Implement this when you are writing a custom class that will be used by other users.
There is performance costs associated with Finalize method.	There is no performance costs associated with Dispose method.
For Example, // Implementing Finalize method public class MyClass { //At runtime C# destructor is automatically Converted to Finalize method. ~MyClass () { //TO DO: clean up unmanaged objects } }	For Example, // Implementing Dispose method public class MyClass : IDisposable { private bool disposed = false; //Implement IDisposable. public void Dispose() { Dispose(true); } protected virtual void Dispose(bool disposing) { if (!disposed) { if (disposing) { //TO DO: clean up managed objects } //TO DO: clean up unmanaged objects disposed = true; } } }

Q) What is Collections?

For many applications, you want to create and manage groups of related objects.

There are two ways to group objects:

(1) by creating arrays of objects, and

(2) by creating collections of objects.

Arrays are most useful for creating and working with a fixed number of strongly-typed objects.

Collections provide a more flexible way to work with groups of objects. Unlike arrays, the group of objects you work with can grow and shrink dynamically as the needs of the application change. For some collections, you can assign a key to any object that you put into the collection so that you can quickly retrieve the object by using the key.

A collection is a class, so you must declare a new collection before you can add elements to that collection.

A generic collection enforces type safety so that no other data type can be added to it. When you retrieve an element from a generic collection, you do not have to determine its data type or convert it.

There are many types of collections:

1) System.Collections.Generic Classes

2) System.Collections.Concurrent Classes

3) System.Collections Classes

4) Visual Basic Collection Classes

System.Collections will contain the following:

(1) ArrayList: Represents an array of objects whose size is dynamically increased as required. Implements the IList interface using an array whose size is dynamically increased as required.

Syntax:

ArrayList arrLst = new Arraylist();

arrLst.Add();

ArrayList dynamically resizes.

(2) HashTable: Represents a collection of key/value pairs that are organized based on the hash code of the key.

Hashtable ht = new Hashtable();

ht["Name"] = "Shubham";

ht["Address"] = "Bangalore";

(3) Stack: Represents a first in, first out (FIFO) collection of objects.

(4) Queue: Represents a last in, first out (LIFO) collection of objects.

System.Collections.Generic will contain the following:

(1) Dictionary<TKey, TValue>: Represents a collection of key/value pairs that are organized based on the key. E.g:

Dictionary<string, int>() dict = new Dictionary<string, int>(){{“One”,1},{“Two”,2}};

Dictionary is faster than Hashtable.

(2) List<T>: Represents a list of objects that can be accessed by index. Provides methods to search, sort, and modify lists.

(3) Queue<T>: Represents a first in, first out (FIFO) collection of objects.

(4) SortedList<TKey, TValue>: Represents a collection of key/value pairs that are sorted by key based on the associated IComparer<T> implementation.

(5) Stack<T>: Represents a last in, first out (LIFO) collection of objects.

Q) Difference between Hashtable and Dictionary.

1) Dictionary is generic type and hashtable is not a generic type.

2) Dictionary is faster than hashtable because there is no boxing/unboxing in Dictionary but hashtable involves boxing/unboxing.

i. When we retrieve the items from Dictionary we will get the records in the same order we have inserted them. Whereas we add same records in Ha shTable the order is not maintained.

Q) Suppose exception occurs, which page will be redirected?

try

{

}

catch

{

Response.Redirect(Login.aspx);

}

finally

{

Response.Redirect(Home.aspx);

}

Whatever happens, ‘finally’ will be executed and Home.aspx will be redirected.

Q) Can we inherit base class constructor?

Q) What is shadowing?

Shadowing (method hiding):

A method or function of the base class is available to the child (derived) class without the use of the "overriding" keyword. The compiler hides the function or method of the base class. This concept is known as shadowing or method hiding. In the shadowing or method hiding, the child (derived) class has its own version of the function, the same function is also available in the base class.

Example

Public class BaseClass

{

public string GetMethodOwnerName()

{

return "Base Class";

}

public class ChildClass : BaseClass

{

public new string GetMethodOwnerName()

{

return "ChildClass";

}

Q) How to get data from from specific row and column in gridview?

Use OnSelectedIndexChanged event and add following sample code to this event.

aspx code:

<asp:Gridview Id="GrvSample">

<asp:BoundField DataField="AuthName" HeaderText="AuthName" SortExpression="AuthName" />

<asp:BoundField DataField="Title" HeaderText="Title" SortExpression="Title" />

<asp:BoundField DataField="Price" HeaderText="Price" SortExpression="Price" />

<asp:ButtonField Text="Select" CommandName="Select" ItemStyle-Width="150" />

</Columns>

</asp:gridView>

<asp:Label ID="lblValues" runat="server" Text=""></asp:Label>

c# code:

protected void GrvSample_OnSelectedIndexChanged(object sender, EventArgs e)

{

string authName = GrvSample.SelectedRow.Cells[0].Text; //1st column

string title = GrvSample.SelectedRow.Cells[1].Text; //2nd column

string price = GrvSample.SelectedRow.Cells[2].Text; //3rd column..so on

LblAuthName.Text = "Selected Author's name is: " + authName + ", book name is: "+ title + "and price is: " + price;

}

Q) Does event has a return type?

Q) Does the following case is method overloading?

Class C

{

public string somemethod(int a){}

public int somemethod(string b){}

}

No, The above will give compilation error as the return types are different for the same method. For method overloading arguments should be different but not the return type.

Q) How to set paging in gridview?

Use PageIndexChanging event and write the following sample code:

//Implement page indexing

protected void GrvSample_PageIndexChanging(object sender, GridViewPageEventArgs e)

{

GrvSample.PageIndex = e.NewPageIndex;

//GetBooks method will bring the list of books from the database.

GrvSample.DataSource =GetBooks();

GrvSample.DataBind();

}

Q) What is multilevel inheritance? Do you have used in your project.

Class A

{

public void MthdA()

{

Console.WriteLine("Member of A");

}

Class B:A

{

}

Class C:B

{

}

Class Program

{

static void Main(string[] args)

{

C objC = new C();

//Here you can observe that MthA belongs to Class A and it can also be called from C.

//This is multilevel inheritance.

objC.MthdA();

Console.ReadKey();

}

C will have all the features of A, B and C. This is multilevel inheritance.

Q) What is the flow for a control present inside user control (web user control)?

Example:

In ascx page:

<asp:TextBox ID=”TxtSample” runat=”server”></asp:TextBox>

<asp:Button ID=”BtnSample” runat=”server” />

In aspx Page:

When you click the button which is present inside the user control, the flow will happen like this:

1) Events till Page load event of the aspx page will be called first.

2) If master page is present then the same will happen for page load.

3) Then it will come to page load event of the ascx page.

4) After then control event (e.g BtnSample_Click) will be called.

5) Then page_prerender event of aspx page will be called.

6) Then page_prerender event of the ascx page will be called.

Q) Design Patterns

Gang of Four deals about 23 design patterns. These all come under creational, structural and behavioural patterns.

Creational patterns: These patterns deal with the process of objects creation in such a way that they can be decoupled from their implementing system.

1)Abstract Factory pattern:Create instances of several classes belonging to different families

2)Factory pattern: Create instances of derived classes

3)Singleton: Ensures that a class can has only one instance

Structural patterns: These patterns deal with the composition of objects structures. The concept of inheritance is used to compose interfaces and define various ways to compose objects for obtaining new functionalities.

1)Façade : A single class that represents an entire complex system

2) Proxy : Provides a surrogate object, which references to other object

3) Adapter : Match interfaces of different classes

Behavioral patterns: These patterns deal with the process of communication, managing relationships, and responsibilities between objects.

1) Chain of Responsibility: Passes a request among a list or chain of objects.

2) Command: Wraps a request under an object as a command and passed to invoker object.

3) Interpreter

Q) What is the difference between object, var and dynamic?

Q) What are optional and named parameters in c#?

We can specify optional parameters as follows:

public int SomeFunction(string optParam=””, int value=1){}

This function can be called in the following ways:

1) classic way: SomeFunction(“shubh”,2)

2) named way: SomeFunction(value: 2, optParam: “shubh”)

Q) How many modes are available for session state?

There are three modes available for session state.

1) Off

2) Inproc: Session state is stored locally in memory of ASP.NET worker process.

3) State server: The session state is stored outside of the ASP.NET worker process and is managed by windows service. The location of the this service is specified by stateconnection string attribute.

4) Sql server: Session state is stored outside of the ASP.NET worker process in SQL server database. The location of the database is specified using the sqlconnectionstring attribute.

Q) Server controls?

There are three types of server controls.

(1) Html server controls (2) Web server controls (3) Validation controls

Q) runat=’server’ attribute?

This attribute indicates that the element should be treated as a server control. Server controls are tags that are understood by the server.

Q) What is state management technique?

A new instance of the web page is created each time the web page is posted back to the server and this happens because HTTP is stateless protocol. To preserve the values of the controls present on the page or to overcome the “stateless” limitation, ASP.NET provides us a feature to preserve data on both per-page basis and application-wide basis. These features include

1) Viewstate 2) Control state 3) Hidden fields 4) Cookies 5) Query string 6) Session state 7) Application state 8) Profile properties. Again these features are divided into two types. Viewstate, Control state, Hidden fields, Cookies, Query string belong to client-based state management technique. Session state, Application state and Profile properties are server-based state management options.

Q) What is dynamic type?

The dynamic type enables the operations in which it occurs to bypass compile-time type checking. Instead, these operations are resolved at run time. The dynamic type simplifies access to COM APIs such as the Office Automation APIs, and also to dynamic APIs such as IronPython libraries, and to the HTML Document Object Model (DOM).

Type dynamic behaves like type object in most circumstances. However, operations that contain expressions of type dynamic are not resolved or type checked by the compiler. The compiler packages together information about the operation, and that information is later used to evaluate the operation at run time. As part of the process, variables of type dynamic are compiled into variables of type object. Therefore, type dynamic exists only at compile time, not at run time.

Q) What is anonymous type?

Anonymous types provide a convenient way to encapsulate a set of read-only properties into a single object without having to explicitly define a type first. The type name is generated by the compiler and is not available at the source code level. The type of each property is inferred by the compiler.

var is anonymous type.

var v = new {Amount=108, ItemName=”MicromaxMobile”}

Anonymous types typically are used in the select clause of a query expression to return a subset of the properties from each object in the source sequence.

Q) What is var type?

Beginning in Visual C# 3.0, variables that are declared at method scope can have an implicit type var. An implicitly typed local variable is strongly typed just as if you had declared the type yourself, but the compiler determines the type. The following two declarations of i are functionally equivalent:

var i = 10; // implicitly typed
int i = 10; //explicitly typed

The following example shows two query expressions. In the first expression, the use of var is permitted but is not required, because the type of the query result can be stated explicitly as an IEnumerable<string>. However, in the second expression, var must be used because the result is a collection of anonymous types, and the name of that type is not accessible except to the compiler itself.

// Example #1: var is optional because
// the select clause specifies a string
string[] words = { "apple", "strawberry", "grape", "peach", "banana" };
var wordQuery = from word in words
                where word[0] == 'g'
                select word;

// Because each element in the sequence is a string,
// not an anonymous type, var is optional here also.
foreach (string s in wordQuery)
{
    Console.WriteLine(s);
}

// Example #2: var is required because
// the select clause specifies an anonymous type
var custQuery = from cust in customers
                where cust.City == "Phoenix"
                select new { cust.Name, cust.Phone };

Q) What is difference between var and dynamic?

var	dynamic
Introduced in C# 3.0	Introduced in C# 4.0
Statically typed – This means the type of variable declared is decided by the compiler at compile time.	Dynamically typed - This means the type of variable declared is decided by the compiler at runtime time.
Need to initialize at the time of declaration. e.g., var str=”I am a string”; Looking at the value assigned to the variable str, the compiler will treat the variable str as string.	No need to initialize at the time of declaration. e.g., dynamic str; str=”I am a string”; //Works fine and compiles str=2; //Works fine and compiles
Errors are caught at compile time. Since the compiler knows about the type and the methods and properties of the type at the compile time itself	Errors are caught at runtime Since the compiler comes to about the type and the methods and properties of the type at the run time.
Visual Studio shows intellisense since the type of variable assigned is known to compiler.	Intellisense is not available since the type and its related methods and properties can be known at run time only
e.g., var obj1; will throw a compile error since the variable is not initialized. The compiler needs that this variable should be initialized so that it can infer a type from the value.	e.g., dynamic obj1; will compile;
e.g. var obj1=1; will compile var obj1=” I am a string”; will throw error since the compiler has already decided that the type of obj1 is System.Int32 when the value 1 was assigned to it. Now assigning a string value to it violates the type safety.	e.g. dynamic obj1=1; will compile and run dynamic obj1=” I am a string”; will compile and run since the compiler creates the type for obj1 as System.Int32 and then recreates the type as string when the value “I am a string” was assigned to it. This code will work fine.

Q) What is connection pool?

Connection pooling reduces the number of times that new connections must be opened. The pooler maintains ownership of the physical connection. It manages connections by keeping alive a set of active connections for each given connection configuration. Whenever a user calls Open on a connection, the pooler looks for an available connection in the pool. If a pooled connection is available, it returns it to the caller instead of opening a new connection. When the application calls Close on the connection, the pooler returns it to the pooled set of active connections instead of closing it. Once the connection is returned to the pool, it is ready to be reused on the next Open call.

Only connections with the same configuration can be pooled. By default, connection pooling is enabled in ADO.NET.

Q) What is an application pool?

The <applicationPools> element contains configuration settings for all application pools running on your Internet Information Services (IIS) 7 or later server. An application pool defines a group of one or more worker processes, configured with common settings that serve requests to one or more applications that are assigned to that application pool. Because application pools allow a set of Web applications to share one or more similarly configured worker processes, they provide a convenient way to isolate a set of Web applications from other Web applications on the server computer. Process boundaries separate each worker process; therefore, application problems in one application pool do not affect Web sites or applications in other application pools. Application pools significantly increase both the reliability and manageability of your Web infrastructure.

What is worker process?

An Internet Information Services (IIS) worker process is a windows process (w3wp.exe) which runs Web applications, and is responsible for handling requests sent to a Web Server for a specific application pool.

IIS 7 lists worker processes with associated application pool names, and provides the following information for each worker process:

1) Application Pool Name. The name of the application pool. In the case of Web gardens, the same application pool may be listed more than once in the grid to account for different worker processes running in the application pool.

2) Process ID. The worker process identifier (ID) associated with the application pool.

3) State. The state of the process, such as starting, running, or stopping.

4) CPU %. The percentage of time that the worker process has used the CPU since last update. This corresponds to CPU Usage in Task Manager.

5) Private Bytes (KB). The current size of memory committed to a worker process, which cannot be shared with other processes. This corresponds to Virtual Memory Size in Windows Task Manager.

6) Virtual Bytes (KB). The current size of the virtual address space for a worker process. This does not correspond to anything in Windows Task Manager.

Q) What are the 4 pillars of any object oriented programming language?

1. Abstraction

2. Inheritance

3. Encapsulation

4. Polymorphism

Q) Abstraction.

It is "To represent the essential feature without representing the background details." Abstraction lets you focus on what the object does instead of how it does. Abstraction provides you a generalized view of your classes or object by providing relevant information. Abstraction is the process of hiding the working style of an object, and showing the information of an object in understandable manner.

Real world Example of Abstraction-1:

Suppose you have an object Mobile Phone. Suppose you have 3 mobile phones as following:-

Nokia 1400 (Features: Calling, SMS)

Nokia 2700 (Features: - Calling, SMS, FM Radio)

Blackberry (Features: - Calling, SMS, FM Radio, MP3)

Abstract information (Necessary and Common Information) for the object "Mobile Phone" is make a call to any number and can send SMS." so that, for mobile phone object you will have abstract class like following:-

abstract class MobilePhone

{

public void Calling () {}

public void SMS () {}

}

public class Nokia1400 : MobilePhone

{

}

public class Nokia1600 : MobilePhone

{

public void FMRadio() {}

}

public class BlackBerry : MobilePhone

{

public sub FMRadio() {}

public sub MP4() {}

}

Abstraction means putting all the variables and methods in a class which are necessary. For example: - Abstract class and abstract method. Abstraction is the common thing.

Real world Example of Abstraction-1:

If somebody in your college tell you to fill application form, you will fill your details like name, address, date of birth, which semester, percentage you have got etc. If some doctor gives you an application to fill the details, you will fill the details like name, address, date of birth, blood group, height and weight.

See in the above example what is the common thing? Age, name, address. So you can create the class which consists of common thing that is called abstract class. That class is not complete and it can be inherited by other class.

Q) Inheritance.

Inheritance enables you to create new classes that reuse, extend, and modify the behavior that is defined in other classes. The class whose members are inherited is called the base class, and the class that inherits those members is called the derived class. A derived class can have only one direct base class (no multiple inheritance). However, inheritance is transitive. If ClassC is derived from ClassB, and ClassB is derived from ClassA, ClassC inherits the members declared in ClassB and ClassA.

Q) Polymorphism.

Polymorphism is often referred to as the third pillar of object-oriented programming, after encapsulation and inheritance. Polymorphism is a Greek word that means "many-shaped" and it has two distinct aspects:

1) At run time, objects of a derived class may be treated as objects of a base class in places such as method parameters and collections or arrays. When this occurs, the object's declared type is no longer identical to its run-time type.

2) Base classes may define and implement virtual methods, and derived classes can override them, which means they provide their own definition and implementation. At run-time, when client code calls the method, the CLR looks up the run-time type of the object, and invokes that override of the virtual method. Thus in your source code you can call a method on a base class, and cause a derived class's version of the method to be executed.

Polymorphism provides following features:

1) It allows you to invoke methods of derived class through base class reference during runtime.

2) It has the ability for classes to provide different implementations of methods that are called through the same name.

Polymorphism is of two types:

1) Compile time polymorphism/Overloading

2) Runtime polymorphism/Overriding

Compile Time Polymorphism: Compile time polymorphism is method and operators overloading. It is also called early binding. In method overloading method performs the different task at the different input parameters.

Runtime Polymorphism: Runtime polymorphism is done using inheritance and virtual functions. Method overriding is called runtime polymorphism. It is also called late binding.

Note: While overriding a method, you can change the behavior of the method for the derived class. Overloading a method simply involves having another method with the same prototype.

Q) Encapsulation.

Wrapping up data member and method together into a single unit (i.e. Class) is called encapsulation. Encapsulation is like enclosing in a capsule. That is enclosing the related operations and data related to an object into that object. Encapsulation is like your bag in which you can keep your pen, book etc. It means this is the property of encapsulating members and functions.

class Bag

{

book;

pen;

ReadBook();

}

Encapsulation means hiding the internal details of an object, i.e. how an object does something. Encapsulation prevents clients from seeing it’s inside view, where the behaviour of the abstraction is implemented. Encapsulation is a technique used to protect the information in an object from the other object.

Hide the data for security such as making the variables as private, and expose the property to access the private data which would be public. So, when you access the property you can validate the data and set it.

Example:

class Demo

{

private int _mark;

public int Mark

{

get { return _mark; }

set { if (_mark > 0) _mark = value; else _mark = 0; }

}

Real world Example of Encapsulation-1:

Let's take example of Mobile Phone and Mobile Phone Manufacturer. Suppose you are a Mobile Phone Manufacturer and you designed and developed a Mobile Phone design(class), now by using machinery you are manufacturing a Mobile Phone(object) for selling, when you sell your Mobile Phone the user only learn how to use the Mobile Phone but not that how this Mobile Phone works.This means that you are creating the class with function and by making object (capsule) of it you are making availability of the functionality of your class by that object and without the interference in the original class.

Real world Example of Encapsulation-2:

TV operation: It is encapsulated with cover and we can operate with remote and no need to open TV and change the channel. Here everything is in private except remote so that anyone can access not to operate and change the things in TV.

Q) Difference between Abstraction and Encapsulation.

Abstraction	Encapsulation
1. Abstraction solves the problem in the design level.	1. Encapsulation solves the problem in the implementation level.
2. Abstraction is used for hiding the unwanted data and giving relevant data.	2. Encapsulation means hiding the code and data into a single unit to protect the data from outside world.
3. Abstraction lets you focus on what the object does instead of how it does.	3. Encapsulation means hiding the internal details or mechanics of how an object does something.
4. Abstraction- Outer layout, used in terms of design. For Example:- Outer Look of a Mobile Phone, like it has a display screen and keypad buttons to dial a number.	4. Encapsulation- Inner layout, used in terms of implementation. For Example:- Inner Implementation detail of a Mobile Phone, how keypad button and Display Screen are connect with each other using circuits.

Q) What is .Net Framework?

.Net framework is a technology on which .Net applications are built and deployed. The framework consists of three main components:

(1) Common Language Runtime.

(2) Framework Base classes (Base Class Library) like System.IO, System.Threading and many more.

(3) User and Program Interface - Like User Interface(ASP.NET, WPF, etc) and Program Interface (C#, J#, VB.NET, F#, etc).

It is used to build and run windows and web applications.

Q) Common Language Runtime

Common Language Runtime (CLR) is a managed execution environment that is part of Microsoft’s .NET framework. CLR manages the execution of programs written in different supported languages.

How it works? The .NET compiler converts the code written in a supported .NET language, such as C# or VB.Net to CIL (Common Intermediate Language) code. During runtime, the CLR converts the CIL code into native code that can be understood by the operating system. It provides services such as memory management, thread management, security management, code verification, compilation and other system services.

Q) Managed code and unmanaged code?

Managed Code: The code which is written in (vb.net, c#, j#) .net framework language is called as managed code which is under the control of CLR. Garbage collector run automatically in managed code. In other words, code that we develop with a language compiler that targets the runtime is called managed code. It benefits from features such as cross-language integration, cross-language exception handling, enhanced security, versioning and deployment support, a simplified model for component interaction, debugging and profiling services.

UnManaged Code: The code which is produced by third party language is called as unmanaged code, which does not run under the control of CLR. Garbage collector will not run in case of unmanaged code.

Q) What is an assembly?

1) An assembly is a fundamental building block of any .NET Framework application. For example, when you build a simple C# application, Visual Studio creates an assembly in the form of a single portable executable (PE) file, specifically an EXE or DLL.

2) An assembly is the smallest unit of reuse, versioning and security.

3) Assemblies contain metadata that describe their own internal version number and details of all the data and object types they contain.

4) Assemblies can be an efficient way to manage resources in larger projects because they are only loaded as they are required. If they are not used, they are not loaded.

Q) What is a metadata?

Metadata includes description of an assembly. Description includes type definitions, version information, external assembly references, security permissions and other standard information. During compile time, metadata is created with MSIL (Microsoft Intermediate Language) and stored in a file called ‘Manifest’. An assembly manifest contains all the metadata needed to specify the assembly's version requirements and security identity, and all metadata needed to define the scope of the assembly and 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 standalone PE file that contains only assembly manifest information.

Benefits of Metadata: Metadata provides great benefits such as self-describing files, language interoperability, type safety and is extensible through attributes.

Q12) Connectionstring description?

1) Data Source - It identifies the server, can be a local machine, machine domain name or IP Address.

2) Initial Catalog - name of the database.

3) Persist Security Info - specifies whether the data source can persist sensitive authentication information such as a password. It can be set as true or false.

4) User ID - name of the user configured in SQL server.

5) Password - password set in SQL server for this User ID.

Q13) What is the difference between string and stringbuilder?

String object is immutable and StringBuilder is mutable. By immutable means that string object cannot be changed. So, if you were to do some string operation involving an append or trim or some other method call to modify your string object, you would really be creating those many new objects of class String. Performance will degrade and hence we will use StringBuilder. If you will store string in StringBuilder and will do some operation, then it will do the operation on this same object and it will not create other object.

Note: Creating more number of objects is expensive because it consumes memory.

Q14) What is struct?

A struct is a value type that contains constructors, constants, fields, methods, properties, events, indexers, operators and nested types.

Syntax: [attributes] [modifiers] struct identifier : <interfaceNames> { }. This is explained below:

(1) attributes (Optional): Additional declarative information.

(2) modifiers (Optional): The allowed modifiers are ‘new’ and the four access modifiers.

(3) identifier: The struct name.

(4) interfacenames (Optional): A list that contains the interfaces implemented by the struct, all separated by commas.

(5) {}: The struct body that contains member declarations.

Example:

public struct Point

{

public int x, y;

public int point(int p1, int p2)

{

x = p1;

y = p2;

}

Some points about structs:

1) Struct is a value type while class is a reference type.

(2) In some scenarios, struct is less expensive than class.

(3) There is no inheritance for structs. But structs can implement interface.

(4) Variables directly contain the data of the struct a while variable of a class type contains a reference to the data. This means that with structs you avoid the overhead of objects in the C# language. You can combine multiple fields. This reduces memory pressure. And it improves performance if the stack is not overwhelmed.

Do structs support inheritance?

No, structs do not support inheritance, but they can implement interfaces.

Q15) What is the main advantage of using inheritance?

Code reuse

Q16) Can we open Web.Config file through URL?

We can’t because it is not served by IIS for security reasons. It contains “database connection string”.

Q17) Can we host Web Service outside of IIS?

We can host web services outside of IIS also. Possibilities are

1) Windows Services

2) Console Applications

3) COM+ components or windows form applications

Q18) What is viewstate and its advantages and disadvantages?

Viewstate is a technique used by ASP.Net web pages to keep the state of the page across post backs. It stores data in a hidden field name _VIEWSTATE inside the page in base 64 encoded format. The viewstate will exist till the life of that page.

Advantage:

1) It does not require any server resource. It is stored at client side.

2) Automatically retains the state of the page.

3) Provides the flexibility to enable or disable at page or control level.

4) Also provide control to check and validate whether the view state data is tampered or not by using EnableViewStateMac.

Disadvantage:

1) Since the view state data is stored inside the page it increases the network overhead as all the data travel along with the page.

2) As data is stored in encoded format, it can be easily decoded. So it is advised not to store sensitive data in viewstate.

EnableViewState?

Gets or sets a value indicating whether the page maintains its view state, and the view state of any server controls it contains, when the current page request ends.The default is true. Either we can set this property in page directive for the whole page or we can set it inside individual controls.

What is EnableViewStateMac?

Gets or sets a value indicating whether ASP.NET should check message authentication codes (MAC) in the page’s view state when the page is posted back from the client. The main purpose is to check whether the data present on the client is tampered or not. By default the value is true.

Q) Does C# support multiple inheritance ? If No Why?

No. Because of ‘Diamond’ problem.

Q) What is diamond problem?

Why C# does not support multiple inheritance?

In object-oriented programming language with multiple inheritance and knowledge organization, the diamond problem is an ambiguity that arises when two classes B and C inherit from A, and class D inherits from both B and C. If a method in D calls a method defined in A (and does not override the method), and B and C have overridden that method differently, then from which class does it inherit: B, or C?

Q) What is interface?

An interface contains only the signatures of methods, properties, events or indexers. A class or struct that implements the interface must implement the members of the interface that are specified in the interface definition. In the following example, classImplementationClass must implement a method named SampleMethod that has no parameters and returns void.

interface ISampleInterface
{
    void SampleMethod();
}

class ImplementationClass : ISampleInterface
{
    // Explicit interface member implementation:
    void ISampleInterface.SampleMethod()
    {
        // Method implementation.
    }

    static void Main()
    {
        // Declare an interface instance.
        ISampleInterface obj = new ImplementationClass();

        // Call the member.
        obj.SampleMethod();
    }
}

Q) Why we need interface?

(1) To extend the functionality of base class.

(2) To take the advantages of polymorphism by using interfaces.

(3) For naming convention, say you are working in team and each member has to use one common method for e.g Draw. So we will define this method in IDraw Interface and every member can use this method.

(4) To implement multiple inheritance because multiple inheritance is not allowed in C#.

(5) For removing dependency (E.g ZEWS solution).

Q) Can we use access specifiers for interface?

No. All methods in an interface are public by default so we cannot use any access specifiers. If we will use, it will show error.

Q) Access specifiers for classes?

Classes at the namespace level can be public or internal only. We can't use private, protected or protected internal for classes at namespace level. All access specifiers are applicable for nested classes ie. nested classes can be public, private, protected or internal or protected internal.We can use any access specifiers for methods and nested classes.

Q) What is keyword for inherit and implements in c#?

Colon i.e ':' is used for both. If you are implementing more than one interface for a class then use comma. When inheritance of a class and implementation of interface has to be done at same time then priority will be for inheritance of class than implementation of interface. For example check the example shown below:

Example: For inheriting MainClass and implementing three interfaces ->

Class Test : MainClass, ITest1, ITest2, ITest3

{

// Write the code here

}

Q) Details about interface?

An interface is a named collection of method definitions and their signatures without implementation.

(1) Only methods and signatures(i.e declaration part and not implementation) are required.

(2) Interface members must be methods, properties, events or type definitions.

(3) All methods in an interface are public by default so we cannot use any access specifiers otherwise it will generate error.

(4) A class that implements the interface agrees to implement all of the methods defined in the interface.

Q) Difference between abstract class and interface?

(1) An interface only provides declaration but abstract class can provide complete, default and/or just the details that have to be overridden.

(2) A class can implement more than one interface but can inherit only one abstract class.

(3) An interface cannot have access specifiers but abstract class can contain the access modifiers for subs, properties and functions.

(4) Requires more time to find the actual method in the corresponding classes. But abstract classes are fast.

(5) No fields can be defined in interfaces. An abstract class can have fields and constraints defined.

(6) If we add a new method to an Interface then we have to track down all the implementations of the interface and define implementation for the new method. If we add a new method to an abstract class then we have the option of providing default implementation and therefore all the existing code might work properly.

(7) If various implementations only share method signatures then it is better to use Interfaces.If various implementations are of the same kind and use common behaviour or status then abstract class is better to use.

In conclusion we can say that interface is an abstract class which provides only declaration and not any other thing.

Q) In which cases we will not be able to create object of class?

We will not be able to create an object of a class in the following scenarios:

(1) When you declare the constructor as private.

(2) When you declare the class as static.

(3) When you declare the class as abstract.

(4) When you declare the class as not class but interface.

Q) Garbage Collection in Short?

The .Net Framework garbage collector manages the allocation and deallocation of memory for your application. Each time we create a new object, the common language runtime allocates a memory for the object from the managed heap. As long as address space is available in the managed heap, the runtime continues to allocate space for the new objects. However, the memory is limited. Eventually the garbage collector must perform a collection in order to free some memory. The garbage collector’s optimizing engine determines the best time to perform a collection, based upon the allocations being made. While performing a collection, it checks for objects in the managed heap that are no longer being used by the application and performs the necessary operation to reclaim their memory.

In short, Garbage collection is the process of managing the allocation and release of memory which are no longer in use.

Q) Global Assembly Cache?

Each computer wherein the common language runtime is installed has a machine-wide code called the Global Assembly cache. This global assembly cache stores .NET assembly specifically designated to be shared by several applications on that computer.

For .NET 4.0, GAC is situated in the following location:

%windir%\Microsoft.Net\assembly\

For previous version of .NET Framework, the GAC is present in the following location:

%windir%\assembly\

Installation of an assembly into GAC:

gacutil –i <completeAssemblyPath>

Un-installation of an assembly from GAC:

gacutil –u <assemblyName>

Link: http://www.codeproject.com/Articles/4352/Demystifying-the-NET-Global-Assembly-Cache

Q) How .Net Framework make transitions between managed and unmanaged code?

.NET Framework uses DCOM for making transition between managed and unmanaged code.

Q) What is type safe?

Type safety means that the compiler will validate types while compiling, and throw an error if you try to assign the wrong type to a variable.

In computer science, type safety is the extent to which a programming language discourages or prevents type errors. A type error is erroneous or undesirable program behaviour caused by a discrepancy between differing data types for the program's constants, variables, and methods (functions),for e.g., treating an integer (int) as a floating-point number (float).

Q) What is type casting (or casting)?

Conversion between data types is called as type casting. In implicit conversion (from smaller to large data types for example, int to float or from base class to derived class), type casting is not required as it will not throw error but while explicit conversion casting is required.

Example:

C#:

double x = 1234.7;
int a = (int)x; // cast double to int

VB:

Dim str As String = "300"

Dim num As Integer = CInt(str)

C#.Net supports 2 types of typecasting:

1)Implicit type casting.

2)Explicit type casting.

Implicit type casting is under control or CLR. Converting from Lower data types into Higher data types is called as Implicit type casting.

For Example:

Byte---->Long(Implicit)

Explicit type casting is under control of programmer. Converting from Higher data types into Lower data types is called as Explicit type casting.

For Example:

long---->int(Explicit)

C#.Net supports 4 types of Explicit Type Casting:

1)C++ style of TypeCasting. E.g. a = (int)x;

2)Converting. E.g. Convert.ToString, Convert.ToInt32.

3)Parsing. E.g. Int.Parse() in c# and Integer.Parse()

4)Boxing & UnBoxing.

Q) What is Option Explicit?

1) If used, the Option Explicit statement must appear in a file before any other source code statements.

2) When Option Explicit appears in a file, you must explicitly declare all variables using the Dim or ReDim statements. If you attempt to use an undeclared variable name, an error occurs at compile time.

Q) Why C# is a strongly typed language?

Before a value can be stored in a variable, the type of the variable must be declared and also type of value must be matched with the data type. If datatype is not correct then it will throw compile time error.

Q) Conversions?

1) Implicit conversion: No special syntax is required because the conversion type is safe and no date will be lost. Examples include conversions from smaller to larger integral types, and conversions from derived classes to base classes.

2) Explicit conversion: Explicit conversion require a cast operator. Casting is required when information might be lost in the conversion, or when the conversion might not succeed for other reasons. Typical examples include numeric conversion to a a type that has less precision or a smaller range, and conversion of a base class instance to a derived class.Using explicit conversions we are actually letting the compiler know that we know there is possible information loss but still we need to make this conversion. So if we need to convert a long type to an integer type we need to cast it explicitly.

3) User defined conversions: User defined conversions are performed by special methods that you can define to enable implicit and explicit conversions between custom types that do-not have a base class-derived class relationship.

4) Conversion with helper classes: To convert between non-compatible types, such as integers and System.Datetime objects, or hexadecimal strings and byte arrays, we can use the System.BitConverter class, the System.Convert class and the parse methods of the built-in numeric types, such as Int32.Parse.

Q) Can a class can contain a class?

Yes, nested classes can exist.

Q) Suppose you have set two master pages for a content pages, in which event you will set master pages for a content page dynamically?

Page_PreInit event of the content page.

void Page_PreInit(Object sender, EventArgs e)
{
this.MasterPageFile = "~/NewMaster.master";
}

Q) What is static modifier?

When we use the static keyword before a class name:

1) We specify that the class will only have static member variables and methods.

2) Such classes cannot be instantiated as they don’t need to: they cannot have instance variables.

3) Also, an important point to note is that such static classes are sealed by default, which means they cannot be inherited further.

4) They cannot contain Instance Constructors or simply constructors as we know that they are associated with objects and operates on data when an object is created.

When we use the static keyword before a method or variable name:

1) Static members and variable can reside in non-static class.

2) An important point to note is that the static methods inside a class can only use static member variables of that class.

Example:

Suppose you have a private variable in MyClass which is not static:

class MyClass
{
    // non-static instance member variable
    private int a;
    //static member variable
    private static int b;
    //static method
    public static void DoSomething()
    {
      //this will result in compilation error as “a” has no memory
      a = a + 1;
      //this works fine since “b” is static
      b = b + 1;
    }
}

Now, we will call the DoSomething method as: MyClass.DoSomething();

Note that we have not created any instance of the class, so the private variable "a" has no memory as when we call a static method for a class, only the static variables are present in the memory (in the Static part). Instance variables, such as “a” in the above example, will only be created when we create an instance of the class using the “new” keyword, as:

Imp Information about static modifier:

1) Only one copy of static fields and events exists.

2) Static members are often used to represent data or calculations that do not change in response to object state; for instance, a math library might contain static methods for calculating sine and cosine.

Q) Why we create an object or objects of a class?

We create different objects to store and manipulate different data at different times. When we don’t want any change or manipulation of the data, that is the data will be same for example in case of cosine, sine etc. then we will create static class.

Q) Where we can use static classes?

1) We can use static class when all the members and variables are static.

2) Use a static class as a unit of organization for methods not associated with particular objects.

Q) Advantages of static class.

Static class makes implementation simple and faster because there is no need to create object.

Q) What is default constructor?

A constructor which accepts no parameter is called the default constructor or parameterless constructor.

Q) What are private assemblies and shared assemblies?

A private assembly is used only by a single application, and is stored in that application's install directory (or a subdirectory therein). A shared assembly is one that can be referenced by more than one application. In order to share an assembly, the assembly must be explicitly built for this purpose by giving it a cryptographically strong name (referred to as a strong name). By contrast, a private assembly name need only be unique within the application that uses it.

Q) What is the Microsoft Intermediate Language (MSIL)?

MSIL is the CPU-independent instruction set into which .NET Framework programs are compiled. It contains instructions for loading, storing, initializing, and calling methods on objects. Combined with metadata and the common type system, MSIL allows for true cross-language integration.Prior to execution, MSIL is converted to machine code. It is not interpreted.

Q) What are private assemblies and shared assemblies?

Q) Difference between dataadapter, datareader and dataset?

DataReader : This is best used when you just want to fetch data in readonly mode , populate your business entity and close the reader. This is really fast. You cannot do update with datareader. It is forward only, read only and works in connected mode. it keeps single row at a time.

DataAdapter : You can Read/Update the data with dataadapters but it is less faster when reading the data then Datareader. It can do read/Write in both sides and works in disconneted mode. It acts as a bridge between dataset and datasource. Dataset doesnot interact with datasource, dataadapter fills does this work.

Dataset: DataSet is a disconnected orient architecture that means there is no need of active connections during work with datasets and it is a collection of DataTables and relations between tables. It is used to hold multiple tables with data. You can select data form tables, create views based on table and ask child rows over relations. Also DataSet provides you with rich features like saving data as XML and loading XML data.

Q) Which is the base class for all classes in .Net Framework?

System.object

Q) Difference between stack and heap.

1) They are both stored in Computer's RAM.

2) Stack is used for static memory allocation while heap is used for dynamic memory allocation.

3) Memory block in stack will be freed when thread is terminated while heap is freed after application termination.

4) Memory block in stack will be freed automatically but heap memory will be freed by garbage collector.

3) The stack is much faster than heap.

6) Memory allocation and deallocation is done using LIFO(Last In First Out) in stack while heap can be reached at any time.

Q) Reference type and value type?

Value types:

1) Value types can be created at compile time.

2) Stored in stack memory.

3) Garbage collector can't access the stack

4) Value types holds the data directly

5) No default values will be stored in value types

Examples for value types: Predefined data types, structures, enums, int

Reference types:

1) Reference types can be created at run time.

2) Stored in heap memory

3) Garbage collector can access heap

4) Reference types holds the data indirectly

5) Reference types holds default value

Examples for reference types: Classes, objects, Arrays, Indexers, Interfaces, String

Q) AutoEventWireup

The ASP.NET page framework also supports an automatic way to associate page events and methods.The disadvantage of the AutoEventWireup attribute is that it requires that the page event handlers have specific, predictable names. This limits your flexibility in how you name your event handlers. Therefore, in Visual Studio, the AutoEventWireup attribute is set to false by default and the designer generates explicit code to bind page events to methods. If you do set AutoEventWireup to true, Visual Studio will generate code to bind the events and the page framework will automatically call events based on their names. This can result in the same event code being called twice when the page runs. As a consequence, you should always leave AutoEventWireup set to false when working in Visual Studio.

Q) Differences between ExecuteReader, ExecuteNonQuery AND ExecuteScalar?

ExecuteNonQuery: ExecuteNonQuery method will return number of rows affected with INSERT, DELETE or UPDATE operations. This ExecuteNonQuery method will be used only for insert, update and delete, Create, and SET statements.

ExecuteScalar: ExecuteScalar will return single row single column value i.e. single value, on execution of SQL Query or Stored procedure using command object. It’s very fast to retrieve single values from database.

ExecuteReader: ExecuteReader will be used to return the set of rows, on execution of SQL Query or Stored procedure using command object. This one is forward only retrieval of records and it is used to read the table values from first to last.

Q) Differences between datagrid, repeater, gridview and listview?

Controls Functionalities	ListView	GridView	DataList	Repeater
Paging	Supported	Supported	Not Supported	Not Supported
Data Grouping	Supported	Not Supported	Supported	Not Supported
Provide Flexible Layout	Supported	Not Supported	Supported	Supported
Update, Delete	Supported	Supported	Not Supported	Not Supported
Insert	Supported	Not Supported	Not Supported	Not Supported
Sorting	Supported	Supported	Supported	Supported
Introduced in ASP.NET version	3.5	2.0	1.1	1.1

Q) What is the difference between datatable.Clone() and datatable.copy()?

The main difference between clone and copy is that Clone will copy the structure of a datatable whereas Copy will copy the complete structure as well as data.

Q) What is the difference between const and readonly?

1) Const value must be known at compile time while readonly value can be assigned at run time.

2) Const must be assigned when declared but readonly can be assigned either at declaration time or in the constructor.

2) Const can't be modified within a class or out of the class where as readonly can be modified in same class.

2) We can use read only when some function value needs to be calculated at run time.

3) For example:

static class NonModifiableDeclarationSet {
    internal const int SomeInteger = 5;
    internal const int SomeOtherInteger = SomeInteger * 10; //constant expression
    // won't compile:
    //internal const double SomeFloatingPointValue = System.Math.Acos(-1d);
    // will work:
    internal static readonly double SomeFloatingPointValue = System.Math.Acos(-1d);
}

Q) What is the difference between Asp.Net user control (ascx) and Asp.Net web page (aspx)?

1) User control contains an @Control directive while web page contains an @Page directive.

2) User controls cannot run as standalone files like aspx pages. They must be embedded inside aspx pages if they are needed.

3) Base class for User Control is System.Web.UI.UserControl and for Web forms, it is System.Web.UI.Page

4) The user control does not have html, body or form elements in it.

5) User control extension is ascx and web page or web forms extension is aspx.

Q) Similarities between User control and web page?

1) Use of existing web server controls which Asp.Net offers.

2) The event model that Asp.Net provides.

3) A user control can include codes such as binding from database etc...

Q) Differences between master page and user control?

1) Master Pages are used to provide the consistent layout and common behaviour for multiple pages in your applications. Then you can add the Contentplaceholder to add child pages custom content. User Controls are used at times when you need the functionality in your web pages which is not possible using the built-In web server controls then user can create his own controls called user controls using asp.net built-in controls. User controls are those with .aspx extensions and you can share it in the application.

2) A master page is page template whereas user control encapsulates a piece of functionality.

3) Extension for master page is .master and extension for user control is .ascx.

4) Master pages can be referenced using Web.Config file also or dynamically by writing code in PreInit event. User controls can be attached dynamically using LoadControl method. PreInit event is not mandatory in their case for dynamic attachment.

5) User control can be used inside master page but master page cannot be used inside user control.

6) Master page inherits System.Web.UI.MasterPage and this MasterPage class inherits System.Web.UI.UserControl

Q) what is session state?

Session state is a state management technique which provides facility to store information in server memory on a per client basis.

Advantages:

1) Easy to implement and can store any kind of object.

2) Session is secure and transparent from the user.

3) Stores client data separately.

Disadvantages:

1) Performance overhead in case of large data/user, because session data is stored in server memory.

2) Overhead involved in serializing and deserializing session data, because in the case of StateServer and SqlServer session modes, we need to serialize the objects

before storing them.

System.Web.SessionState.HttpSessionState class provides the built-in session object in ASP.NET pages.

Storing a value in session:

Session["UserName"] = TxtUser.text;

Retrieving a value from session:

If (Session["UserName"]) != null)

{

LblUser.Text = Session["UserName"];

}

else

{

// Do something

}

Storing a dataset:

Session["DataSet"] = objDataSet;

Retrieving a DataSet session:

If (Session["DataSet"]) != null)

{

DataSet myDataSet = (DataSet)Session["DataSet"];

}

else

{

// Do something

}

When a client communicates with a server, only the session ID is transmitted between them. When the client requests for data, ASP.NET looks for the session ID and

retrieves the corresponding data from the state provider.

In the web.config, <SessionState> elements are used for setting the configuration of the session. Some of them are Mode, Timeout, StateConnectionString, CustomProvider,

etc.

Session state can only be used when enableSessionState is set to true, either in a configuration file or in the Page directive. Please also make sure that

System.Web.SessionStateModule or a custom session state module is included in the <configuration>\<system.web>\<httpModules> section in the application configuration.

Q) Where session value is stored?

ASP.NET saves the value in state provider. For every session state, there is a state provider. Session State mode - State provider

1) InProc - In-memory object

2) StateServer - Aspnet_state.exe

3) SQLserver - Database

4) Custom - Custom Provider

There is also one mode "Off". If we select this option the session will be disabled for the application.

Q What is global.asax file?

1) The Global.asax, also known as the ASP.NET application file, is used to serve application level and session level events.

2) Global.asax is compiled to its own assembly – if you publish the web project from Visual Studio, you can find App_global.asax.dll in the bin directory, otherwise it will go to c:\Windows\Microsoft.NET\Framework\v4.0.30319\Temporary ASP.NET Files\<appname>.

3) Global_asax class inherits from HttpApplication class.

4) The Global.asax file, also known as the ASP.NET application file, is an optional file that contains code for responding to application-level events raised by ASP.NET or by HttpModules.

5) The Global.asax file resides in the root directory of an ASP.NET-based application.

6) The Global.asax file is parsed and dynamically compiled by ASP.NET.

7) The Global.asax file itself is configured so that any direct URL request for it is automatically rejected; external users cannot download or view the code written within it.

8) The Global.asax file does not need recompilation if no changes have been made to it. There can be only one Global.asax file per application and it should be located in the application's root directory only.

9) The Global.asax contains two types of events those are:

a) Events which are fired for every request: Application_BeginRequest(), Application_AuthenticateRequest(), Application_AuthorizeRequest(), etc.

b) Events which are not fired for every request: Application_Start(), Session_Start(), Application_Error(), Application_End(), Session_End(), Application_Disposed().

10) The Global.asax file is optional. If you do not define the file, the ASP.NET page framework assumes that you have not defined any application or session event handlers.

Q) Difference between string.Empty, “” and null?

1) String.empty is initialised to “” at runtime. We cannot use in switch but we can use in if.

Example: value = String.Empty; if (value==””){ }

2) String.Empty does not create object while “” creates an object.

3) Null means absence of data. Null is not a value, it is a state indicating that object value is unknown or non-existent.

Q) Difference between user control and custom control?

1) Custom Control Inherits from WebControl to achieve some extra functionality. These are classes.User Control is collection or grouping of WebControls. It is similar to aspx page and is used to place common markup code in a common file.

2) Custom controls provide more atomic control (i.e custom controls are more flexible) as compared to user controls.

3) Custom controls are dlls which are precompiled but user controls need to be compiled every time with the aspx page in which it has been embedded.

4) If there is need of application specific control, then user controls will serve the purpose but when we need redistributable controls, custom controls are the best ones.

5) Custom control derives from control class(System.Web.UI.Control)While User control derives from user control (System.Web.UI.UserControl).

6) Has full textbox support and can't be added to the toolbox.

Q What is enum?

Enumeration is a user defined integer type that allows us to give user friendly names. It is generally used when we have limited number of numeric choices and want to convey these choices with user friendly names.It makes our code cleaner, easy to maintain and easy to use as Visual studio provides its intellisense. Example:

Enum day

{

Sunday, Monday, Tuesday

}

In the above example, Sunday is 0, Monday is 1 and Tuesday is 2.

By default C# enum member is set 0 and each of the subsequent member is incremented by one. The type of an enumerator is int by default. However, we can declare explicitly a base type for each C# enum. The valid base types are: Byte, sbyte, short, ushort, int, uint, long, ulong. Example:

enum shape : long

{

Circle,

Square =100,

Triangle

}

Note:

1) We can’t declare char as an underlying data type for enum objects because char stores Unicode characters, but enum objects data type can only be number.

2) enum can’t be derived from any other type except that of type byte, sbyte, short, ushort,int, uint, long, or ulong.

3) By default, enum is a sealed class and therefore sticks to all the rules that a sealed class follows, so no class can derive from enum, i.e., a sealed type.

Q) New keyword

There are two uses of new keyword:

1) For creating object

A obj = new A();

2) For hiding the base class method from derived class simply declare the derived class method with new keyword.

Example:

Class A

{

public void Test( {Console.WriteLine(“Class A”)});

}

Class B:A

{

//Hidiing the method of A

public new void Test( {Console.WriteLine(“Class B”)});

}

Class program

{

static void main(string[] args)

{

A ObjA = new A();

B ObjB = new B();

ObjA.Test(); //output-> Class A

ObjB.Test(); //output-> Class B

ObjA = new B();

ObjA.Test(); //output-> Class A

}

Note: If you will not use new keyword, compiler will show warning.

Q) Override keyword

A method can be overridden by declaring it virtual in parent class i.e in order for an instance of a derived class to completely take over a class member from a base class, the base class has to declare that member as virtual. This is accomplished by adding the virtual keyword before the return type of the member. A derived class then has the option of using the override keyword, instead of new, to replace the base class implementation with its own. For example:

public class BaseClass

{

public virtual void DoWork() { }

public virtual int WorkProperty

{

get { return 0; }

}

public class DerivedClass : BaseClass

{

public override void DoWork() { }

public override int WorkProperty

{

get { return 0; }

}

Q) Virtual keyword

Fields cannot be virtual; only methods, properties, events and indexers can be virtual. When a derived class overrides a virtual member, that member is called even when an instance of that class is being accessed as an instance of the base class.

Q) Summary about New, override, virtual?

1. The virtual keyword is used to modify a method, property, indexer, or event declared in the base class and allow it to be overridden in the derived class.

2. The override keyword is used to extend or modify a virtual/abstract method, property, indexer, or event of base class into derived class.

3 The new keyword is used to hide a method, property, indexer, or event of base class into derived class.

Q) What is the difference between Server.Transfer and Response.Redirect?

1) Response.Redirect changes the url in the browser while Server.Transfer retains the original url in the browser. It just replaces the contents of the previous page with the new one.

2) Response.Redirect used for both aspx and html pages. Server.Transfer used only for aspx page.

3) Response.Redirect involves a round trip to the server while Server.Transfer conserve server resources by avoiding the round trip. It just changes the focus of the web server to a different page and transfers the page processing to a different page.

4) Response.Redirect can be used to redirect a user to an external website. Server.Transfer used only for sites running on the same server. It cannot be used to redirect the user to a page running on a different server.

Q) What is the difference between Response.redirect and Response.Redirectpermanent and server.transfer?

The Response.Redirect generates Response code as 302 whereas RedirectParmanent returns 301. Server. transfer generates response as 200.

1. Response.Redirect() : Search Engine will take this redirection as Temporary(Status 301) and always keep Page1 in its cache.

2. Response.RedirectParmanent() : Search Engine will take this a permanent redirection(Status 302) and will remove Page1 from its database and include Page2 for better performance on search.

3. Server.Transfer() : Search Engine will be unaware of any redirection been took place (Status 200) and will keep Page1 to its database. It will think Page1 is producing the output response of Page2.

When to use:

Response.Redirect is perfect when your page is temporarily changed and will again be reverted to original within a short span of time.

Response.RedirectParmanent() when you are thinking of deleting the original page totally after the search engines changes its database.

Server.Transfer() when you are thinking of keeping the page for ever, and to let search engine unaware of this redirection.

Q) What is the difference between HiddenField and ViewState?

1) The HiddenField control is used to store a value that needs to be persisted across posts to the server. Normally view state is used to maintain the state of a Web Form page.

2) ViewState stores the 64 bit encrypted value but Hidden field does not do any encryption.

3) Hidden field is used to store small amount of data as compared to viewstate.

4) ViewState internally uses hidden field. It is managed by ASP.NET Engine and is encrypted by default.

Q) Explain Page Life Cycle.

(1) PreInit, (2) Init, (3) InitComplete, (4) PreLoad, (5) Load, (6) ControlEvents, (7) LoadComplete, (8) PreRender, (9) PreRenderComplete, (10) SaveStateComplete, (11) RenderComplete, (12) Unload.

PreInit:

1) Check for the IsPostBack property to determine whether this is the first time the page is being processed.

2) Create or recreate dynamic controls.

3) Set master page dynamically.

4) Set the Theme property dynamically.

5) Read or set profile property values.

If Request is postback:

1) The values of the controls have not yet been restored from view state.

2) If you set control property at this stage, its value might be overwritten in the next event.

Init:

1) The Init event of the individual controls occurs first, later the Init event of the Page takes place.

2) This event is used to initialize control properties.

InitComplete:

1) Tracking of the ViewState is turned on in this event.

2) Any changes made to the ViewState in this event are persisted even after the next postback.

PreLoad:

This event processes the postback data that is included with the request.

Load:

In this event the Page object calls the OnLoad method on the Page object itself, later the OnLoad method of the controls is called. Thus Load event of the individual controls occurs after the Load event of the page.

ControlEvents:

1) This event is used to handle specific control events such as a Button control’s Click event or a TextBox control’s TextChanged event.

2) In case of postback, if the page contains validator controls, the Page.IsValid property and the validation of the controls takes place before the firing of individual control events.

LoadComplete:

1) This event occurs after the event handling stage.

2) This event is used for tasks such as loading all other controls on the page.

PreRender:

1) In this event the PreRender event of the page is called first and later for the child control.

2) Usage:This method is used to make final changes to the controls on the page like assigning the DataSourceId and calling the DataBind method.

PreRenderComplete:

1) This event is raised after each control's PreRender property is completed.

SaveStateComplete:

1) This is raised after the control state and view state have been saved for the page and for all controls.

RenderComplete:

1) The page object calls this method on each control which is present on the page.

2) This method writes the control’s markup to send it to the browser.

Unload:

1) This event is raised for each control and then for the Page object.

2) Use this event in controls for final cleanup work, such as closing open database connections, closing open files, etc.

Q) What is the difference between Response.Write() and Response.Output.Write()?

Response.write() just writes/displays the text or string on the web page.

E.g: Response.Write("hi");// Output will be simply hi.

Response.output.write() formats the string in the format specified before displaying it on the web page.

E.g: Response.output.write("Hi I am {0}. I am {1} yrs old.","Shubham","28")

Q) Difference between Stack and heap.

When you declare a variable in a .Net application, it allocates some chunk of memory in the RAM. This memory has three things: the name of the variable, the data type of the variable, and the value of the variable. There are two types of memory allocation: stack and heap. Depending on the data type, the memory is allocated.

Stack: The stack is responsible for keeping track of the running memory needed in your application. In stack memory allocation and deallocation is done using LIFO. In other words memory is allocated and deallocated at only one end of memory i.e. top of the stack. Reference pointers are allocated on stack. Stack memory will be de-allocated when the variable goes out of scope after execution of the method in which it is present.

Heap: Heap is a pile of objects which can be reached at any point of time. Heap is used for dynamic memory allocation. If the requirement is of dynamic memory, it’s allocated on the heap or else it goes on a stack. Heap memory will be de-allocated by the garbage collector.

Example: In order to understand stack and heap, let’s understand what actually happens in the below code internally. ‘Heap’ does not track running memory.

Public void Method1 ()

{

//Line 1

int i=4;

//Line 2

int y=2;

//Line 3

Class obj = new Class ();

}

Explanation of above Code:

1) When Line1 is executed, the compiler allocates memory for the variable i in the stack. (The stack is responsible for keeping track of the running memory needed in your application.)

2) When Line2 is executed, the compiler stacks this memory location on top of the first memory location. (You can think about stack as a series of compartments or boxes put on top of each other.)

3) When Line3 is executed, it creates a pointer on the stack and the actual object is stored on heap.

4) Now finally when the execution control passes the end control, it clears all the memory variables

Q) Why can’t we allocate everything on just one memory type (why two memories- stack and heap)?

If you look closely at “int i = 0”, it holds single value but object data types are complex. Object types hold reference to multiple values and each one of these values must be stored in memory. Object types need dynamic memory while primitive ones need static type memory.

Q) Can we share session value between two Asp.Net applications?

Yes, If we will store session value in Sql server then we can retrieve this value in any other application.

Q) What is overhead?

Overhead is a combination of excess or indirect computation time, memory, bandwidth or other resources that are required to attain a particular goal.

Q) Difference between ToString() and Convert.ToString().

Calling ToString() on an object presumes that the object is not null (since an object needs to exist to call an instance method on it). Convert.ToString() doesn't need to presume the object is not null (as it is a static method on the Convert class), but instead will return String.Empty if it is null.

Q) Why we need to write the the name of the function/method in derived class as already we wrote in abstract class?

BY writing in abstract class,

(1) We are providing abstraction (if some new developer analyzes the code then it will be very easy to identify what are the main methods involved).

(2) For naming convention also.

Q) What is the difference between bool and Boolean? Similarly difference between string and String?

Bool is an alias for System.Boolean.

Same reason for others like string and String (string is an alias for System. String, int is an alias for System.Int32).

Link: http://msdn.microsoft.com/en-us/library/c8f5xwh7(v=vs.80).aspx

Check list of aliases in c#:

http://msdn.microsoft.com/en-us/library/ya5y69ds%28VS.80%29.aspx

Q) Why C# is a strogly typed language?

Before a value can be stored in a variable, the type of the variable must be declared.

Q) Conversions?

2) Explicit conversion: Explicit conversion require a cast operator. Casting is required when information might be lost in the conversion, or when the conversion might not succeed for other reasons. Typical examples include numeric conversion to a type that has less precision or a smaller range, and conversion of a base class instance to a derived class.Using explicit conversions we are actually letting the compiler know that we know there is possible information loss but still we need to make this conversion. So if we need to convert a long type to an integer type we need to cast it explicitly.

Q) What is SqlDataAdapter?

A SqlDataAdapter is a bridge between the data source and the dataset. Select, Update, Insert or Delete operations can be performed by SqlDataAdapter. A SqlDataAdapter contains a connection object and command object. It operates in disconnected mode and opens or closes the connection automatically while reading or writing to a database.

Example:

SqlConnection con = new SqlConnection(constring);

SqlCommand cmd = new SqlCommand(con);

SqlDataAdapter dataAdapt = new SqlDataAdapter(cmd);

Datatable dt = new datatable;

dataAdapt.Fill(dt);

Q) What is non-generic (Systems.Collections)?

The System.Collections namespace contains classes and interfaces that define various collection of objects such as lists, queues, bit arrays, hashtables, and dictionaries., etc. Classes such as ArrayList, BitArray, Comparer, DictionaryBase, etc. interfaces such as ICollection, IComparer, IEnumerable, IEnumerator, IDictionary, etc.

Q) What is generic (Systems.Collections.Generic)?

The System.Collections.Generic namespace contains interfaces and classes that define generic collections which allow users to create strongly typed collections that provide better type safety and performance than non-generic collections. Classes such as Comparer<T>, Dictionary<T>, List<T>. Interfaces such as ICollections<T>, IList<T> etc. Note: T defines the type.

Q) Difference between Generic and Non-Generic?

The main difference between generic and non-generic collections is that generic provides better type safety and performance issues than non-generic.

Example: In List<T>, type will be declared in place of T at compile time only. In List, type is not declared. So, we can add object of any type. Hence, lot of boxing has to be done because it converts all types into one type before doing any operation.

Q) Uses of New keyword?

1) To create object. ClassA objA = new ClassA();

2) To hide the base class method in derived class

Q) How to read XML document?

Step 1: Dataset ds = new dataset(); //Declare a dataset.

Step 2: ds.ReadXml(<path of the XML file>); or ds.ReadXml(ioStream);

Q) What is the difference between new and override?

1) New hides the base class method but through override we can also extend the base class method.

Q) How can we override base class method?

Base class method must be used with abstract or virtual or override modifier. Then only we can override in derived class.

Q) How modifiers can be added in methods?

Modifiers can be added before or after access specifiers.

Q) Can we declare abstract methods in non-abstract class?

No. We can declare abstract methods only in abstract class.

Q) Can we declare non-abstract methods in abstract class?

Yes. We can declare non-abstract as well as abstract methods in abstract classes.

Q) Difference between virtual and abstract?

Virtual method needs body part but abstract may or may no have body part.

Q) Connection pooling.

What is connection pooling?

A connection pool is a cache of database connections maintained so that the connections can be reused when future requests to the database are required.

Why connection pooling?

Connecting to a database server typically consists of several time-consuming steps. A physical channel such as a socket or a named pipe must be established, the initial handshake with the server must occur, the connection string information must be parsed, the connection must be authenticated by the server, checks must be run for enlisting in the current transaction, and so on.

In practice, most applications use only one or a few different configurations for connections. This means that during application execution, many identical connections will be repeatedly opened and closed. To minimize the cost of opening connections, ADO.NET uses an optimization technique called connection pooling. If all the connections are being used, a new connection is made and is added to the pool. Connection pooling also cuts down on the amount of time a user must wait to establish a connection to the database.

How connection pooling works?

The pooler maintains ownership of the physical connection. It manages connections by keeping alive a set of active connections for each given configuration. Whenever a user calls OPEN on a connection, the pooler looks for an available connection in the pool. If a pooled connection is available, it returns it to the caller instead of opening a new connection. When the application calls CLOSE on the connection, the pooler returns it to the pooled set of connections instead of closing it. Once the connection is returned to the pool, it is ready to be used on the next OPEN call.

Some More information about Connection Pooling:

1) By default, a connection string is enabled with connection pooling.

2) By default, the maximum number of pools is 100, minimum is 0.

3) If the connection string is different, new pool will be created.

Q) There are 10000 records. I want to display 5000 records in one gridview and 5000 records in another grid view. What is the process?

SqlConnection con = new SqlConnection (connectionString);

Query1 = “SELECT TOP 5000 * FROM Tbl ORDER BY ID”;

Query2 =” SELECT TOP 5000 * FROM Tbl ORDER BY ID DESC”;

con.Open ();

SqlDataAdapter da1 = new SqlDataAdapter (Query1, con);

SqlDataAdapter da2 = new SqlDataAdapter (Query2, con);

Dataset ds = new Dataset ();

da1.Fill (ds,”dt1”);

da2.Fill (ds,”dt2”);

Grv1.DataSource = ds. Tables [“dt1”];

Grv2.DataSource = ds. Tables [“dt2”];

Grv1.DataBind ();

Grv2.DataBind ();

Q) Garbage Collection.

Advantage of Garbage Collector

1. Allow us to develop an application without having worry to free memory.

2. Allocates memory for objects efficiently on the managed heap.

3. Reclaims the memory for no longer used objects and keeps the free memory for future allocations.

4. Provides memory safety by making sure that an object cannot use the content of another object.

http://www.dotnet-tricks.com/Tutorial/netframework/0L3P131012-.Net-Garbage-Collection-in-depth.html

Key points about Garbage Collector

1. All objects in the heap are allocated from one contiguous range of memory address and heap is divided into generations so that it is easy to eliminate the garbage objects by looking at only a small fraction of the heap.

2. Gen 0 and Gen 1 occupy a single segment known as the ephemeral segment. Gen 2 is a set of further segments and the large object heap is yet another group of segments.

3. Almost, all objects with-in a generation are of the same age.

4. The newest objects are created at higher memory address while oldest memory objects are at lowest memory address within the heap.

5. The allocation pointer for the new objects marks the boundary between the allocated and free memory.

6. Periodically the heap is compacted by removing the dead objects and sliding up the live objects towards the lower memory address end of the heap as shown in above fig.

7. The order of objects (after memory reclaims) in memory remains the same as they were created.

Q) What is satellite assembly?

A Dot NET framework assembly containing resources specific to a given language. Using satellite assemblies, you can place the resources for different languages in different assemblies, and the correct assembly is loaded into memory only if the user selects to view the application in that language. In general, assemblies should contain culture-neutral resources. If you want to localize your assembly (for example use different strings for different locales) you should use satellite assemblies. You are likely to use them when creating a multilingual (UI) application. Satellite assemblies provide you with the capability of designing and deploying your solution to multiple cultures, rather than hard coding strings, bitmaps, etc., into your main application. You are likely to use them when creating a multilingual (UI) application. Satellite assemblies provide you with the capability of designing and deploying your solution to multiple cultures, rather than hard coding strings, bitmaps, etc., into your main application.

Q) Threading

What is thread: A thread executes code synchronously- a set of instructions processed by the CPU “first-in-first-out”. This can execute any kind of code, be it updating of the GUI, processing calculations or waiting for user input. GUI programs typically rely on two layers:

1) Processing stack, which includes any code or task executed in the background, and

2) User interface, which is supposed to give the user a means for instructing the program to execute tasks, and receiving timely “updates” or indications of progress.

How threading works: A multitasking operation system divides the available processor time among the processes and threads that need it. A thread is executed in the given time slice, and then it is suspended and execution starts for next thread/process in the queue. When the OS switches from one thread to another, it saves thread context for preempted thread and loads the thread context for the thread to execute. The length of time slice that is allocated for a thread depends on the OS, the processor, as also on the priority of the task itself.

Multithreading: CPU can switch between two or more thread contexts so two tasks (e.g calculation and GUI update) can be executed in parallel or asynchronously. For example, a program can make full use of a multi-core processor by instructing each core to process a separate task, or a chunk of the whole task. This results in improved performance.

Advantages:

1) One of the advantages of using the threads is that you can have multiple activities happening simultaneously.

2) Another advantage is that a developer can make use of threads to achieve faster computations by doing two different computations in two threads instead of serially one after the other.

Working with threads: In .NET framework, System. Threading namespace provides classes and interfaces that enable multi-threaded programming. This namespace provides:

1) Thread Pool class for managing group of threads,

2) Timer class to enable calling of delegates after a certain amount of time,

3) A Mutex class for synchronizing mutually exclusive threads, along with classes for scheduling the threads, sending wait notifications and deadlock resolutions.

Thread Priority or scheduling threads: Every thread has a thread priority assigned to it. Threads created within the common language runtime are initially assigned the priority of ThreadPriority.Normal. Threads created outside the runtime retain the priority they had before they entered the managed environment. You can get or set the priority of any thread with the Thread.Priority property.

Thread Safety: When we are working in a multithreaded environment, we need to maintain that no thread leaves in an invalid state. Thread safety basically means the member of an object always maintain a valid state when used concurrently by multiple threads. There are multiple ways of doing it .The Mutex class or the Monitor classes of the Framework enable this, and more information on both is available in the Framework SDK documentation. Locking is essential in threaded programs. It restricts code from being executed by more than one thread at the same time. The syntax for the lock would be as follows:

Using System;

Using System.Threading;

//define the namespace, class etc.

...

public somemethod (...)

{ ...

lock(this)

{

Console.WriteLine (“Inside the lock now”);

...

}

Example of lock:

class Account

{

decimal balance;

private Object thisLock = new Object();

public void Withdraw(decimal amount)

{

lock (thisLock)

{

if (amount > balance)

{

throw new Exception("Insufficient funds");

}

balance -= amount;

}

Syntax:

In C#:

Thread objThread = new Thread (new ThreadStart (className.methodName));

In VB:

Dim objThread as New Thread (Address Of className.methodName)

Example of threading: Common uses for it include any possibly lengthy operations such as:

1) Downloading images or information from the Internet. Or

2) Assembling a list of files from various directories. Or

3) Computing CPU-heavy results.

using System;

using System.Threading;

public class ServerClass

{

// The method that will be called when the thread is started.

public void Instance Method()

{

Console.WriteLine("You are in InstranceMethod.Running on Thread A”);

Console.WriteLine("Thread A Going to Sleep Zzzzzzzz”);

// Pause for a moment to provide a delay to make threads more apparent.

Thread. Sleep (3000);

Console.WriteLine ("You are Back in InstanceMethod.Running on Thread A");

}

public static void StaticMethod()

{

Console.WriteLine("You are in StaticMethod. Running on Thread B.");

// Pause for a moment to provide a delay to make threads more apparent.

Console.WriteLine("Thread B Going to Sleep Zzzzzzzz");

Thread.Sleep(5000);

Console.WriteLine("You are back in static method. Running on Thread B");

}

public class Simple

{

public static int Main(String[] args)

{

Console.WriteLine ("Thread Simple Sample");

ServerClass serverObject = new ServerClass();

// Create the thread object, passing in the

// serverObject.InstanceMethod method using a ThreadStart delegate.

Thread InstanceCaller = new

Thread(new ThreadStart(serverObject.InstanceMethod));

// Start the thread.

InstanceCaller.Start();

Console.WriteLine("The Main() thread calls this " +

"after starting the new InstanceCaller thread.");

// Create the thread object, passing in the

// serverObject.StaticMethod method using a ThreadStart delegate.

Thread StaticCaller = new Thread(new

ThreadStart(ServerClass.StaticMethod));

// Start the thread.

StaticCaller.Start();

Console.WriteLine("The Main () thread calls this " +

"after starting the new StaticCaller threads.");

return 0;

}

Q) Late Binding and Early Binding

Overriding, reflection i.e dynamic types are all late binding. Overloading is early binding.

Q) Difference between HTTP request methods: post and get?

GET - Requests data from a specified resource.

POST - Submits data to be processed to a specified resource.

Get Method:

1) GET requests can be cached

1) GET requests remain in the browser history

2) GET requests can be bookmarked

3) GET requests should never be used when dealing with sensitive data

4) GET requests have length restrictions

5) GET requests should be used only to retrieve data

Post method:

1) POST requests are never cached

2) POST requests do not remain in the browser history

3) POST requests cannot be bookmarked

4) POST requests have no restrictions on data length

Q) What is COM?

COM is used to communicate between two computers which are on intranet. DCOM is for net.

COM is used by developers to create reusable software components, link components together to build applications, and take advantage of Windows services. COM objects can be created with a variety of programming languages. Object-oriented languages, such as C++, provide programming mechanisms that simplify the implementation of COM objects. The family of COM technologies includes COM+, Distributed COM (DCOM) and ActiveX® Controls. Basically a third party dll. Scenario like in visual studio- c++ we are using by the reference of third party dll. This is a com component.

Q) Do the following is method overloading?

String Method1 ()

{ }

Integer Method2 ()

{ }

No, it will show error. Functions which are to be overloaded cant return values of different data types. Parameters and data types for parameters (arguments) can be different but return type should be same.

Q) Difference between session and application?

Application variables are the variables which remain common for the whole application… Their value can be used across the whole application and they die only when the application stops or probably when they are killed forcibly. The ideal example for these kind of variables are site counter… We can find out how many people accessed a particular site since the time it went live via application variables and incrementing the same on every session start.

Session variables are variables which remain common for the whole application but for one particular user. They also can be used across the whole application. But they die when a particular user session ends or probably when they are killed forcibly. The ideal example for this kind of variable are user id. You might want to show "Welcome Vishal" on every page of your site till vishal logs off… So in session start you set a variable to "Welcome Vishal" and kill it on session end.

All these methods like session start, session end, application start, application end are found in

global.asax and that’s the reason global.asax is one for the whole ASP.Net application.

Q) CType

Ctype is used to convert the variable from one type to another.

Example(1):

dim x as integer

x=10

dim str as string

str=ctype(x,str)

Example(2):

Dim lblcontent As Label = CType(Master.FindControl("lblcontent"), Label)

Here master page control lblcontent is found and its converted to label control using ctype

Q) Optional Parameter

In VB:

You can specify that a procedure parameter is optional and no argument has to be supplied for it when the procedure is called. Optional parameters are indicated by the Optional keyword in the procedure definition. The following rules apply:

● Every optional parameter in the procedure definition must specify a default value.

● The default value for an optional parameter must be a constant expression.

● Every parameter following an optional parameter in the procedure definition must also be optional.

Syntax:

Sub sub name(ByVal parameter 1 As data type 1, Optional ByVal parameter 2 As data type 2 = default value)

Example:

Sub notify(ByVal company As String, Optional ByVal office As String = "QJZ")
    If office = "QJZ" Then
        Debug.WriteLine("office not supplied -- using Headquarters")
        office = "Headquarters"
    End If
    ' Insert code to notify headquarters or specified office.
End Sub

In C#:

n C# 4.0. Named and optional parameters are really two distinct features, and allow us to either omit parameters which have a defined default value, and/or to pass parameters by name rather than position. Named parameters are passed by name instead of relying on its position in the parameter list, whereas optional parameters allow us to omit arguments to members without having to define a specific overload matching.

Q) What is mean by MSIL?

MSIL or IL stands for Microsoft Intermediate Language; if you compile managed code, the compiler translates your source code into Microsoft intermediate language. MSIL is platform independent language which can be converted to native code while installing software or at runtime by using Just-in compiler.

Q) What is mean by CTS?

Common type system defines how types are declared, used, and managed in the runtime, and is also an important part of the runtime's support for cross-language integration. CTS is responsible for defining types that can be used across the .Net Languages. CTS Provides the data types, values, object types. This helps developers to develop applications in different languages.

For example, an integer variable in C# is written as int, whereas in VB.Net it is written as integer. Therefore in .Net Framework you have single class called System.Int32 to interpret these variables.

Q) What is mean by CLS?

Common Language Specification is the subset of CTS; it is specification that defines the set rules and guidelines that all supporting language should follow. It integrate in such a way that programs written in any language can interoperate with one another.

Q) What is mean by JIT?

Just In Time(JIT) compilers which compile the IL code to native executable code (.exe or .dll) for the specific machine and OS. JIT are slightly different from traditional compilers as they compile the IL to native code only when desired e.g., when a function is called, IL of function's body is converted to native code; just in time of need. If same function is called next time, the CLR uses the same copy of native code without re-compiling. As JIT are aware of processor and OS exactly at runtime, they can optimize the code extremely efficiently resulting in very robust applications.

8. What are different types of JIT?

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 functions that are called at runtime. However, these compiled functions are removed when they are not required.

Normal-JIT - Normal-JIT compiles only those functions that are called at runtime and they are stored in cache. If same function is called next time, the CLR uses the same copy of compiled code without recompiling.

Q) What are different type's assemblies?

Private assembly- Private assembly is used within your application and it is installed at the same time as the application itself. It will be located in the same directory as the application or subdirectories thereof.

Shared assembly- Shared assemblies are used by several application. Shared assembly must have version number and unique name and it is usually installed in GAC (Global assembly cache). It reduces the need for disk space and memory space.

Q) What are parts of assembly manifests?

● Identity - Name, version, culture and public key

● A list of files - Files belonging to the assembly, it can have one or more files.

● Lists of referenced assemblies - all assemblies referenced by the assembly are documented inside the manifest.

● Set of permission requests- these are the permission needed to run the assembly.

● Exported types - It describes the structures, class with properties, method and events. It is used to create instance of the class.

Q) What is portable executable (PE)?

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.

Q) How Garbage collector will get memory from OS?

When execution engine starts, GC will initialize segment of memory for its operation. GC reserves memory in segment, each segment is 16MB. When we run out of segments we reserve a new segment. If a segment of memory is not in use, it will be deleted.

Q) What is mean by LOH?

LOH-(Large Object Heap). If size of the object are very high(>64KB) then it will be stored in different segment of memory called as LOH. GC will treat the large objects differently from small objects.

Q) What are situations GC will be called?

1. If user forcefully calls System.GC.Collect

2. System is in low memory situation

3. Memory allocation exceeds the Generation0 threshold

Q) What is mean by value type and Reference type?

Value type- Value type stores their value directly to memory address. Value type's values are allocated on the stack memory.

Reference type - Reference type stores the reference to the value's memory address. Reference type values are allocated on heap memory.

Q) What is mean by Boxing and Unboxing?

Boxing - Converting value type variable to reference type is called as boxing

UnBoxing - Converting reference type variable to value type is called as unboxing

           int vType = 35;
            object rType;
            //Boxing process
            rType = vType;
            //Unboxing process
            vType =(int) rType;

Q) What is difference between System exception and Application exception?

All exceptions are derived from the Exception base class. Where Exception class is derived from the Object class. Both System and Application exception are derived from exception class but it has difference between them. System exceptions are thrown by the CLR where as Application exceptions are thrown by Application.

System Exception	Application Exception
System exceptions are thrown by CLR	Application exceptions are thrown by Application
E.g OutOfMemoryException, NullReferenceException,etc	E.g User defined exception are created to throw application's exception and user defined exceptions are derived from ApplicationException

Q) What is Reflection?

.Net compilers store metadata information(types defined) about the assemblies inside the assembly itself. Using this metadata we can load an assembly dynamically (at runtime), get information about its containing types, instantiate these types and call methods.

"Reflection" is a mechanism using which we can load an assembly dynamically and call its method. The System.Reflection is the root namespace that contains classes to implement the reflection. The Assembly class is the one which is used to represent the assembly in .Net environment.

Example:

static void Main(string[] args)
        {
            // Load an assembly from file
            Assembly myAssembly = Assembly.LoadFrom("MyService.dll");
            // Get the types contained in the assembly and print their names
            Type[] types = myAssembly.GetTypes();
            foreach (Type type in types)
            {
                Console.WriteLine(type.FullName);
                //Get the members(methods) present inside each type
                foreach (MemberInfo member in type.GetMembers())
                {
                    Console.WriteLine("   "+member.Name);
                }
            }
            Console.ReadLine();
        }

Q) If we have two different version of same assembly in GAC how do we make a choice?

using < bindingRedirect > tag in App.config file

<assemblyIdentity name="AssemblyVersionExample"

publicKeyToken="7c779e284ebe2e8c"

culture="neutral" />

<bindingRedirect oldVersion="1.0.0.20"

newVersion="1.0.0.10"/>

</dependentAssembly>

</assemblyBinding>

</runtime>

</configuration>

37. What is mean by Dll Hell?

DLL hell means deploying the same DLL in your application multiple times. In windows application dlls are shared across multiple application. Suppose when App1 is using MyAssembly.dll and it is working fine. Suppose I am installing new application App2 which also having assembly MyAssembly.dll, while installing App2 it will override the old assembly with new MyAssembly.dll. Now only App2 will function properly where as App1 which depends on MyAssembly.dll will fail. This is called as Dll hell. It can be solved by assembly versioning.

Q) How's the DLL Hell problem solved in .NET?

Assembly versioning allows the application to specify not only the library it needs to run (which was available under Win32), but also the version of the assembly.

Q) Can we override static method?

No, compiler will not allow overriding the static method.

Q) What are uses of static class and method?

1. Compiler will not allow creating the instance of the class

2. Static class also makes the implementation simpler and faster

3. Cannot inherit a static class since it is sealed

Q) Can you allow class to be inherited, but prevent the method from being overridden?

Yes, just leave the class public and make the method sealed.

Q) Will sealed class allows inheritance, if not why?

Sealed means it is not inheritable

Q) What are the advantages of Private constructor?

1. Private constructor will prevent the user from creating the instance of the class which contains only static members.

2. Private constructor are used for implementing the singleton pattern

Q) While using inheritance, derived class constructor will call base class constructor?

Yes, base class constructor will be called before child class constructor

Q) Overloaded constructor will call default constructor internally?

No, overload constructor will not call default constructor

Q) What is difference between Overrides and Overridable?

Overridable (VB.Net)/ virtual (C#) is used in parent class to indicate that a method can be overridden. Overrides(VB.Net)/ override(C#) is used in the child class to indicate that you are overriding a method.

Q) What is operator overloading?

Operator overloading is used to provide a custom functionality to existing operators. For Example +,-,* and / operators are used for mathematical functionality. But we can overload these operators to perform custom operation on classes or structure.

Example:

To concatenate the two strings we have to use Concat method

Dim str1, str2, str3 As String
        str1 = "Hello"
        str2 = "world"
        str3 = String.Concat(str1, str2)

But .Net provides in build operator overloading for string we can use â€˜+â€™ operator for concatenating the string value

str3=str1+str2

Similarly we can also implement operator overloading for classes or structure

Employee3= Employee1 + Employee2

Q) Sealed alternative in VB?

NotInheritable

Q) Serialization.

Serialization is the process by which we can save the state of the object by converting the object into some serial data format, such as XML or binary format . These data can then be stored in database, files, memory etc.

In the language of computer in context of data storage and transmission, serialization is the process of translating data stuctures or objects into a format that can be stored in a file or memory buffer, or transmitted across a network connection link and resurrected in the same or another computer environment.

When you create an object in .Net Framework application, you dont need to think about how the data is stored in memory, because .Net Framework takes care of that for you. However for transmission you need to store it in different format. This conversion is called serialization. Below is a simple code of serializing the object.

            MyObject objObject = new MyObject();
            objObject.Value = 100;
            // Serialization using SoapFormatter
            SoapFormatter formatter = new SoapFormatter();
            Stream objFileStream = new FileStream("c:\\MyFile.xml", FileMode.Create,
            FileAccess.Write, FileShare.None);
            formatter.Serialize(objFileStream, objObject);
            objFileStream.Close();

Desirialization is the reverse process of serialization. Below is simple code which shows how to deserialize an object.
            //De-Serialization
            Stream objNewFileStream = new FileStream("c:\\MyFile.xml", FileMode.Open,
            FileAccess.Read, FileShare.Read);
            MyObject objObject =(MyObject)formatter.Deserialize(objNewFileStream);
            objNewFileStream.Close();

Q) Array syntax and initialization.

In C#:

int[] arr = new int[10]{8,7,6,5,4,3,2,1};

In VB.Net:

Dim arr(10) As Integer ={1,2,3,4,5,6}

Q) Properties

class TimePeriod
{
    private double seconds;

    public double Hours
    {
        get { return seconds / 3600; }
        set { seconds = value * 3600; }
    }
}

// Auto-Impl Properties for trivial get and set
public double TotalPurchases { get; set; }

Q) Web Service

The software field is following the way like this. First functional programming came, then OOPS programming to apply reusability, extensibility. Then everything was solved but there was need of communication between different applications. So web service was introduced for this.

Web service is an application that is designed to interact directly with other applications over the internet. Web Service is language independent and Web Services communicate by using standard web protocols and data formats, such as

1) HTTP – Hyper Text Transfer Protocol

2) SOAP – Simple Object Access Protocol

3) XML – EXtensible Markup Language

Advantages of Web Service: Web Service messages are formatted as XML, a standard way for communication between two incompatible system. And this message is sent via HTTP, so that they can reach to any machine on the internet without being blocked by firewall.

Examples for Web Service:

1) Weather Reporting: You can use Weather Reporting web service to display weather information in your personal website.

2) Stock Quote: You can display latest update of Share market with Stock Quote on your web site.

3) News Headline: You can display latest news update by using News Headline Web Service in your website.

In summary you can any use any web service which is available to use. You can make your own web service and let others use it. Example you can make Free SMS Sending Service with footer with your advertisement, so whosoever use this service indirectly advertise your company. You can apply your ideas in N no. of ways to take advantage of it.

If web service is created on local host, its address will be like this:

http://localhost/SampleWebService/Service.asmx

Q) What is SOAP?

SOAP (simple object access protocol) is a remote function call that invokes method and execute them on Remote machine and translate the object communication into XML format. In short, SOAP is a way by which method calls are translated into XML format and sent via HTTP.

Q) What is WSDL?

WSDL stands for Web Service Description Language, a standard by which a web service can tell clients what messages it accepts and which results it will return.

WSDL contains every detail regarding using web service and Method and Properties provided by web service and URLs from which those methods can be accessed and Data Types used. If we will type the following in browser, we can see the wsdl for any web service present.

<web service address>?wsdl

Q) What is UDDI?

UDDI (Universal Description Discovery and Integration) allows you to find web services by connecting to a directory.

Q) What is Discovery or .Disco Files?

Discovery files are used to group common services together on a web server. Discovery files .Disco and .VsDisco are XML based files that contains link in the form of URLs to resources that provides discovery information for a web service. Disco File contains URL for the WSDL, URL for the documentation and URL to which SOAP messages should be sent.

Q) Difference between reflection and dynamic?

1) Both reflection and dynamic are used when we want to operate on an object during runtime.

2) Reflection is used to inspect meta-data of an object. It also has the ability to invoke members of an object on runtime.

3) Dynamic is a keyword which was introduced in .NET 4.0. It evaluates object calls during runtime. So until the method calls are made, compiler is least bothered if those methods or properties etc exist or not.

4) Dynamic uses reflection internally. It caches the method calls made thus improving performance to a certain extent.

5) Reflection can invoke both public and private members of an object while dynamic can only invoke public members.

Below is the detail comparison table which shows in which scenario they are suited.

	Reflection	Dynamic
Inspect ( Meta-data)	Yes	No
Invoke Public members	Yes	Yes
Invoke Private members	Yes	No
Caching	No	Yes

Q) DataReader vs DataAdapter vs Dataset

DataReader: DataReader is used to read the data from database and it is a read and forward only connection oriented architecture during fetch of data from database. DataReader is used to iterate through result set that came from server and it will read one record at a time and hence memory consumption will be less and it will fetch the data very fast when compared with dataset. Generally we will use ExecuteReader object to bind data to datareader.

DataSet: DataSet is based on disconnected orient architecture. It means that there is no need of active connections during work with datasets and it is a collection of DataTables and relations between tables. It is used to hold multiple tables with data. You can select data form tables, create views based on table and ask child rows over relations. Also DataSet provides you with rich features like saving data as XML and loading XML data.

DataAdapter: DataAdapter will acts as a Bridge between DataSet and database. This dataadapter object is used to read the data from database and bind that data to dataset. Dataadapter is a disconnected oriented architecture.

Q) Q) Can I overload int32 and int64 parameters?

Yes

void method1(Int32 a)

{

Console.WriteLine(a.ToString());

}

void method1(Int64 b)

{

Console.WriteLine(b.ToString());

}

Q) What is protected internal? How to access the class in another assembly?

Definition: It is an access specifier in C#. Access is limited to the current assembly or types derived in other assembly.

How to Access:

1) Create one project (SomeProject) and inside it, create one class with public specifier (e.g public class A).

2) Create a method with access specifier as protected internal () inside this class.

3) Now create another project (AnotherProject) and take reference of the project (SomeProject)
already created.

4) Create a class and inherit the class present in the referenced assembly. Now we can call
the method present in the parent class directly. No need to create object of
the parent class.

Q) You have a big page. So you will divide into two pages. In first page you have next button. In second page you have previous button. How you will persist the data of first page when you click on previous button of second page.

Ans: Through Session as there are two different aspx pages.

Q) What is background garbage collection?

In background garbage collection, ephemeral generations (0 and 1) are collected as needed while the collection of generation 2 is in progress. There is no setting for background garbage collection; it is automatically enabled with concurrent garbage collection. Background garbage collection is a replacement for concurrent garbage collection. As with concurrent garbage collection, background garbage collection is performed on a dedicated thread and is applicable only to generation 2 collections.

NOTE:

1) Background garbage collection is available only in the .NET Framework 4 and later versions.

2) Background garbage collection is not currently available for server garbage collection.

Q) What is App domain?

Operating and runtime environments typically provide some form of isolation between applications. For example, Windows uses process to isolate applications. This isolation is necessary to ensure that code running in one application cannot adversely affect, other unrelated applications.

Definition of AppDomain: An AppDomain provides a layer of isolation within a process. Everything you usually think of as "per program" (static variables etc) is actually per-AppDomain. This is useful for:

1) Plugins (you can unload an AppDomain, but not an assembly within an AppDomain).

2) Security (you can run a set of code with specific trust levels).

3) Isolation (you can run different versions of assemblies etc).

Why we need AppDomain?

Application domains provide a flexible and secure method of isolating running applications. Application domains are usually created and manipulated by run-time hosts. Occasionally, you may want your application to programmatically interact with your application domains, for example, to unload a component without having to stop your application from running.

Example: In IIS some web application is running and after some time due to some bug web application crashes, hence IIS should also crash. Hence while programming IIS we can use AppDomain for running web applications and when it crashes, it will unload this specific AppDomain while saving the IIS from crashing.

Real time Scenario:

You are writing a real-time system that processes data received from instruments (e.g. various blood analyzers). Some of the processing steps are done by various libraries written by various companies and could fail because a type of instrument is malfunctioning, a bug in the code, etc. You could use an application domain to isolate 3rd party processing failures, and simply unload problematic processing’s when they happen, leaving the core of the system to continue functioning and process data.

Application domains have the following properties:

1) An assembly must be loaded into an application domain before it can be executed.

2) Faults in one application domain cannot affect other code running in another application domain.

3) Individual applications can be stopped and code unloaded without stopping the entire process. You cannot unload individual assemblies or types, only entire application domains.

Code:

//Create an application Domain:

System. AppDomain newDomain = System.AppDomain.CreateDomain ("NewApplicationDomain");

//Load and Execute an assembly:

newDomain.ExecuteAssembly(@"path of exe file");

//Unload the application domain:

System.AppDomain.Unload(newDomain);

Links:

1) http://liviutrifoi.wordpress.com/tag/c-appdomain-tutorial/

2) http://msdn.microsoft.com/en-us/library/ms173139(v=vs.80).aspx

Q) Validation Controls

All the validation controls inherit from the base class BaseValidator, which is part of the class library namespace System.Web.UI.WebControls.

1) Required Field Validator

<asp:RequiredFieldValidator id="validTxtName runat="server"
controlToValidate="txtName" errorMessage="Name must be entered" display="static"></asp:RequiredFieldValidator>

2) Regular Expression Validator

<asp:RegularExpressionValidator id="regvH" runat="server" display="static" controlToValidate="txtH" errorMessage="Hours must be 1-3 digits only"
validationExpression="\d{1,3}"> </asp:RegularExpressionValidator>

3) Compare Validator

<asp:CompareValidator id="comvR" runat="server" display="static"
controlToValidate="txtR" errorMessage="Rate must be numeric"
type="Double" operator="DataTypeCheck"></asp:CompareValidator>

4) Range Validator

<asp:RangeValidator id="ranvDependents" runat="server" display="static" controlToValidate="txtDependents" errorMessage="Must be from 0 to 10"
type="Integer" minimumValue=0 maximumValue=10> </asp:RangeValidator>

5) Custom validator

<asp:CustomValidator id="cusvDeptNum" runat="server" display="static" controlToValidate="txtDeptNum" onServerValidate="validateDeptNum"
errorMessage="Must be in multiples of 10" > </asp:CustomValidator>

6) Validation Summary

<asp:ValidationSummary id="valSummary" runat="server" headerText="Please correct the following errors" display="static" showSummary= "True" />

Q) Deadlock

A deadlock occurs when two or more tasks permanently block each other by each task having a lock on resource which the other tasks are trying to lock. The following graph presents a high level of a deadlock state where:

1) Task T1 has a lock on resource R1 (indicated by the arrow from R1 to T1) and has requested a lock on resource R2 (indicated by the arrow from T1 to R2)

2) Task T2 has a lock on resource R2 (indicated by the arrow R2 to T2) and has requested a lock on resource R1 (indicated by the arrow from T2 to R1)

3) Because neither task can continue until a resource is available and neither resource can be released until a task continues, a deadlock state exists.

Example:

static object object1 = new object();

static object object2 = new object();

public static void ObliviousFunction()

{

lock (object1)

{

Thread.Sleep(1000); // Wait for the blind to lead

lock (object2)

{

}

public static void BlindFunction()

{

lock (object2)

{

Thread.Sleep(1000); // Wait for oblivion

lock (object1)

{

}

public static void Main()

{

Thread thread1 = new Thread((ThreadStart)ObliviousFunction);

Thread therad2 = new Thread((ThreadStart)BlindFunction);

thread1.Start();

thread2.Start();

while (true)

{

// Stare at the two threads in deadlock.

}

Solution :

The simplest way to avoid deadlock is to use a timeout value .

You can use the Monitor class (system.Threading.Monitor) to set a timeout during acquiring a lock.

Ex. in C#

if(Monitor.TryEnter(this, 500))

{

// critical section

}

catch (Exceprion ex)

{

}

finally

{

Monitor.Exit();

}

Here the timeout is 500 milliseconds .

If the lock can't be acquired, after 500 miliseconds, timeout occurs and the code exit the Monitor block.

Q) How to convert datatable or dataset to datareader?

Datatable dt;

DataTableReader reader = dt.CreateDataReader();

Q) Can we extend String class?

No. because it is sealed.

Q) ToString()

It belongs to System and not to System.String. It is overriddable because it is defined as

public virtual string ToString(){}.

Q) Difference between hashtable and dictionary?

1) Hashtable is non generic whether dictionary is generic i.e. dictionary can be used with any data type.

2) Hashtable is slower than dictionary because it requires boxing and unboxing.

3) Hashtable returns null if we try to find a key which does not exist but dictionary returns error

If we try to find a key which does not exist.

4) All the members in a hashtable are thread safe. In dictionary only public static members are thread safe.

5) System.Collections is the namespace for Hashtable and System.Collections.Generic is the namespace for Dictionary.

6) Syntax:

HashTable: HashTable objHash = new HashTable ();

Dictionary: Dictionary<Tkey, TValue> objDict = new Dictionary<TKey, TValue> ();

Q) Difference between ArrayList and List?

1) “System.Collections” is the namespace for ArrayList and “System.Collections.Generic" is the namespace for List<T>.

2) By using both the ArrayList and Generic List we can store any type of objects. Consider that you are intended to store only the integer values. In this case when we use ArrayList, we can store any type of objects (i.e., Integer, String or some custom objects).

Example:

ArrayList objarList=new ArrayList ();

objarList. Add (123);

objarList. Add ("senthil"); // will compile but throw runtime error.

It won't throw any compile time error. It will throw only run time error when we iterate values in the array list by using for each. But when we use the Generic List, we can restrict in the compile time itself. If you are intended to store only integer values, it will allow storing only integer values. If you try to store any other value other than integer, then it will throw compile time error.

List<int> objList=new List<int> ();

objList. Add (123);

objList. Add ("senthil") // Will result in compile time error.

3) Whenever you are adding the objects in the ArrayList, at that time boxing will happen. Whenever you are accessing the objects from the ArrayList, at that time unboxing will happen. So it will hurt the performance. But in case of Generic List there will not be any Boxing or UnBoxing problem and also it will provide the better type safety.

Q) Difference between array and array list.

1) Arrays are strongly typed whereas Array-Lists are not strongly typed.

2) Elements in Arrays have to be of same data type (int, string, double, char, bool…). Elements in Array-List can have a combination of combined data types or single data type. Note: If Array-List has combined data types then type cast is must.

3) Arrays are fixed specified length size therefore they cannot be resized dynamically during runtime. Array-List can resize dynamically during runtime.

Q) Class A inherits Class B and Class B inherits Class C ?

It is possible, class C can access all the properties and methods present in Class A and Class B.

Q) What is a private constructor?

A private constructor is a special instance constructor. It is generally used in classes that contain static members only.

1) A class containing private constructor cannot be inherited.

2) A class containing private constructor cannot be instantiated.

3) Many times we do not want to create instances of certain classes, common routine classes.

Q) What is c#?

1) C# (pronounced "C sharp") is a simple, modern, object-oriented, and type-safe programming language.

Q) What are three different types of comment in c#?

1) Single line \\

2) Mutli line \* *\

3) Page/Xml Comments \\\

Q) What are the modifiers in c#?

1) Abstract

2) Sealed

3) Virtual

4) Const

5) Event

6) Extern

7) Override

8) Readonly

9) Static

10) New

Q) Differences between singleton pattern and static implementations:

1) we can implement interface with Singleton class but not with Static class.

2) Singleton object stores in Heap but, static object stores in stack

3) Static class provides better performance than Singleton pattern, because static methods are bonded on compile time.

4) When you need a class with full OO capability , chose Singleton, while if you just need to store bunch of static methods together, than use static class.

Q) What is the use of enumerated data type?

An enumerated data type is another user defined type which provides a way for attaching names to numbers thereby increasing comprehensibility of the code. The enum keyword automatically enumerates a list of words by assigning them values 0, 1, 2, and so on.

Q) What are the types of access modifiers?

Public, Private, Protected, Internal, Protected Internal

Q) Difference between IEnumerable vs IQueryable in .NET C#.

Difference: The difference is that IQueryable<T> is the interface that allows LINQ-to-SQL (LINQ.-to-anything really) to work. So if you further refine your query on an IQueryable<T>, that query will be executed in the database, if possible.

For the IEnumerable<T> case, it will be LINQ-to-object, meaning that all objects matching the original query will have to be loaded into memory from the database. And then filter it as per your requirement.

Example:

IEnumerable<Student> students = myModel.GetStudent ();

Var studentsOver25 = students. Where (p => p.ID >= 25);

What happens here is the database loads all of the students, and passes them across to your program. Your program then filters the data. In essence, the database does a “SELECT * FROM Student”, and returns EVERY Student to you. And then put a filter of ID >= 25. This will load all records of student to memory and then put filter on it.

IQueryable<Student> students = myModel.GetStudent ();

Var studentsOver25 = students. Where (p => p.ID >= 25);

Code looks quite same but difference in execution database does a “SELECT * FROM Student where ID >= 25” from a performance standpoint it will return only record with ID > 25 .

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