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NET framework Comparison

2012-08-09T07:04:00.005-07:00

NET framework Comparison

NET framework 2.0:

It brings a lot of evolution in class of the framework and refactor control including the support of

Generics

Anonymous methods

Partial class

Nullable type

The new API gives a fine grain control on the behavior of the runtime with regards to multithreading, memory allocation, assembly loading and more

Full 64-bit support for both the x64 and the IA64 hardware platforms

New personalization features for ASP.NET, such as support for themes, skins and webparts.Many additional and improved ASP.NET web controls.

New data controls with declarative data binding.

New personalization features for ASP.NET, such as support for themes, skins and webparts.

.NET framework 3.0:

Also called WinFX,includes a new set of managed code APIs that are an integral part of Windows Vista and Windows Server 2008 operating systems and provides

Windows Presentation Foundation (WPF), formerly code-named Avalon; a new user interface subsystem and API based on XML and vector graphics, which will make use of 3D computer graphics hardware and Direct3D technologies.

Windows Communication Foundation (WCF), formerly code-named Indigo; a service-oriented messaging system which allows programs to interoperate locally or remotely similar to web services.

Windows Workflow Foundation (WWF) allows for building of task automation and integrated transactions using workflows.

Windows Workflow Foundation (WF) allows for building of task automation and integrated transactions using workflows.

Windows CardSpace, formerly called InfoCard; a software component which securely stores a person's digital identities and provides a unified interface for choosing the identity for a particular transaction, such as logging in to a website

Windows CardSpace (WCS), formerly code-named InfoCard; a software component which securely stores a person's digital identities and provides a unified interface for choosing the identity for a particular transaction, such as logging in to a website.

.NET framework 3.0:

Also called WinFX,includes a new set of managed code APIs that are an integral part of Windows Vista and Windows Server 2008 operating systems and provides

Windows Communication Foundation (WCF), formerly called Indigo; a service-oriented messaging system which allows programs to interoperate locally or remotely similar to web services.

Windows Presentation Foundation (WPF), formerly called Avalon; a new user interface subsystem and API based on XML and vector graphics, which uses 3D computer graphics hardware and Direct3D technologies.

Windows Workflow Foundation (WF) allows for building of task automation and integrated transactions using workflows.

.NET framework 3.5:
It implement Linq evolution in language. So we have the folowing evolution in class:

Linq for SQL, XML, Dataset, Object

Addin system

p2p base class

Active directory

ASP.NET Ajax

Anonymous types with static type inference

Paging support for ADO.NET

ADO.NET synchronization API to synchronize local caches and server side datastores

Asynchronous network I/O API

Support for HTTP pipelining and syndication feeds.

New System.CodeDom namespace.

Sealed Class In C#

2012-08-09T07:04:00.002-07:00

In C#, the sealed modifier is used to define a class as sealed. In Visual Basic .NET, NotInheritable keyword serves the purpose of sealed. If a class is derived from a sealed class, compiler throws an error.

Ex:

// Sealed class

sealed class clsSealedClass

{

}

· But if you try to use this class as a base class you will get error.

// Error will generate

sealed class clsMyClass: clsSealedClass

{

}

· This example demonstrate how to use the sealed class

using System;

class clsMyClass

{

static void Main()

{

clsSealedClass oclsSealedClass = new clsSealedClass ();

int total = oclsSealedClass.Add(4, 5);

Console.WriteLine("Total = " + total.ToString());

}

// Sealed class

sealed class clsSealedClass

{

public int Add(int x, int y)

{

return x + y;

}

Abstract Class In C#

2012-08-09T07:03:00.002-07:00

· Class cannot be instantiated but only used as based class.

· But another class can inherit from an abstract class and can create their instances

· we can implement methods, fields, and properties in the abstract class that can be used by the child class

· Abstract class can't be static.

· Abstract class is used for inheritance.

· Abstract class can't be sealed.

· Abstract or virtual members can't be private, as we can't override it.

· Abstract class can be inherited from an abstract class but the methods in the base class have to be declared abstract.

· Abstract method and properties do not have any functionality. The derived class defines their full functionality.

Ex:

namespace abstract_class

{

class Program

{

public abstract class clsAbstract

{

public abstract int sum(int a, int b);

public abstract int subt(int a, int b);

public void Display()

{

Console.WriteLine("Abstract class");

}

public class clsDerived : clsAbstract

{

// Method overriding

public override int subt(int a, int b)

{

return (a - b);

}

// Method overriding

public override int sum(int a, int b)

{

return (a + b);

}

public void Show()

{

Console.WriteLine("YY class method");

}

static void Main(string[] args)

{

clsDerived obj = new clsDerived ();

// here you can't create instance of a abstract class it is giving error

// clsDerived obj1 = new clsAbstract ();

// clsAbstract obj2 = new clsAbstract ();

// here we have used up level casting

clsAbstract obj3 = new clsDerived ();

// here you don't have access to the Show method of YY

// Because you can only access methods of a reference object only

//obj3.Show();

Console.WriteLine("Calling sum method through reference of base class " + obj3.sum(2,2));

obj.Display();

Console.WriteLine("Subtraction : "+ obj.subt(12, 10));

Console.WriteLine("Addition : " + obj.sum(10, 10));

Console.ReadLine();

}

Interface In C#

2012-08-09T07:02:00.004-07:00

In C# we can define an Interface using Interface key word. Define

//Difine an Interface

interface MyInterface

{

}

Interfaces can be consisting of methods, properties, events, indexers or any combination of those types.
By default all the interface members are Public. So if we use any access modifiers it will prompt compile time error.
Add Interface methods have only declarations, not method implementations.
Class can be inherited by more than one Interface.
Interface can be inherited from other interface as well.
Interface not allows creating instances.

//Difine an Interface

interface MyInterface

{

void MyMethods();

void MyMethods2();

}

class clsMyClass : MyInterface

{

//Can’t create Privet member

public void MyMethods()

{

//Method Implementation

Console.WriteLine("Implement Method MyMethods()");

}

public void MyMethods2()

{

//Method Implementation

Console.WriteLine("Implement Method MyMethods2()");

}

public static void Main()

{

clsMyClass oclsMyClass = new clsMyClass();

oclsMyClass.MyMethods();

oclsMyClass.MyMethods2();

}

When inherit from an Interface need to provide the implementation for all methods. Unless a compile error will be generated.
If the Class or struct is unable to provide the implementation for all methods, which are in the Interface have to be marked as Abstract.

//Difine an Interface

interface MyInterface

{

void MyMethods();

void MyMethods2();

}

class clsMyClass : MyInterface

{

public void MyMethods()

{

//Method Implementation

Console.WriteLine("Implement Method MyMethods()");

}

//No Implementation

abstract public void MyMethods2();

public static void Main()

{

clsMyClass oclsMyClass = new clsMyClass();

oclsMyClass.MyMethods();

oclsMyClass.MyMethods2();

}

Abstract Class vs. Interface in C#

2012-08-09T07:02:00.002-07:00

Abstract Class	Interface
abstract classes are not support multiple inheritance	interface is support multiple inheritance
not allows creating instances	not allows creating instances
Abstract class can contain abstract methods, abstract property as well as other members (just like normal class)	Interface can only contain abstract methods, properties but we don’t need to put abstract and public keyword. All the methods and properties are by default Public.
An abstract class may contain complete or incomplete methods	Interfaces can contain only the signature of a method but no body
abstract class can contain fields, constructors, or destructors and implement properties	An interface cannot contain fields, constructors, or destructors and it has only the property's signature but no implementation
Various access modifiers such as abstract, protected, internal, public, virtual, etc can be used	By default they are public so no need to define

Unified Modeling Language (UML)

2012-08-09T07:01:00.005-07:00

Mostly graphical modelling language that is used to express designs. It is a standardized language in which to specify the artefacts and components of a software system. It is important to understand that the UML describes a notation and not a process.

Types of UML Diagrams

Use Case Diagram
Class Diagram
Object diagram
State diagram
Activity diagram
Sequence diagram
Collaboration diagram
Component diagram
Deployment diagram

Use Case Diagram

2012-08-09T07:01:00.002-07:00

Describe what a system does from the standpoint of an external observer. The emphasis is on what a system does rather than how.
Displays the relationship among actors and use cases

EXAMPLE : A patient calls the clinic to make an appointment for a yearly check up. The receptionist finds the nearest empty time slot in the appointment book and schedules the appointment for that time slot.

Relationships in Use Cases
There are different kinds of relationships between use cases. Reuse of an existing use case using different types of relationships reduces the overall effort required in defining use cases in a system. A similar reuse established using relationships. Use case relationships can be one of the following:

Include: When a use case is depicted as using the functionality of another use case in a diagram, this relationship between the use cases is named as an include relationship.

Extend: In an extend relationship between two use cases, the child use case adds to the existing functionality and characteristics of the parent use case

Generalizations: A generalization relationship is also a parent-child relationship between use cases. The child use case in the generalization relationship has the underlying business process meaning, but is an enhancement of the parent use case.

Use case diagrams are helpful in three areas.
Determining features (requirements)- New use cases often generate new requirements as the system is analyzed and the design takes shape.
Communicating with clients- Their notational simplicity makes use case diagrams a good way for developers to communicate with clients.
Generating test cases- The collection of scenarios for a use case may suggest a suite of test cases for those scenarios.

ASP.NET Interview Questions

2012-08-09T07:00:00.001-07:00

Describe the role of inetinfo.exe, aspnet_isapi.dll andaspnet_wp.exe in the page loading process. inetinfo.exe is theMicrosoft IIS server running, handling ASP.NET requests among other things.When an ASP.NET request is received (usually a file with .aspx extension),the ISAPI filter aspnet_isapi.dll takes care of it by passing the request tothe actual worker process aspnet_wp.exe.
What's the difference between Response.Write() andResponse.Output.Write()? The latter one allows you to write formattedoutput.
What methods are fired during the page load? Init() - when the pageis instantiated, Load() - when the page is loaded into server memory,PreRender() - the brief moment before the page is displayed to the user asHTML, Unload() - when page finishes loading.
Where does the Web page belong in the .NET Framework class hierarchy?System.Web.UI.Page
Where do you store the information about the user's locale? System.Web.UI.Page.Culture
What's the difference between Codebehind="MyCode.aspx.cs" andSrc="MyCode.aspx.cs"? CodeBehind is relevant to Visual Studio.NET only.
What's a bubbled event? When you have a complex control, like DataGrid, writing an event processing routine for each object (cell, button, row, etc.) is quite tedious. The controls can bubble up their eventhandlers, allowing the main DataGrid event handler to take care of its constituents.
Suppose you want a certain ASP.NET function executed on MouseOver overa certain button. Where do you add an event handler? It's the Attributesproperty, the Add function inside that property. So btnSubmit.Attributes.Add("onMouseOver","someClientCode();")
What data type does the RangeValidator control support? Integer,String and Date.
Explain the differences between Server-side and Client-side code? Server-side code runs on the server. Client-side code runs in the clients' browser.
What type of code (server or client) is found in a Code-Behind class? Server-side code.
Should validation (did the user enter a real date) occur server-side or client-side? Why? Client-side. This reduces an additional request to the server to validate the users input.
What does the "EnableViewState" property do? Why would I want it on or off? It enables the viewstate on the page. It allows the page to save the users input on a form.
What is the difference between Server.Transfer and Response.Redirect? Why would I choose one over the other? Server.Transfer is used to post a form to another page. Response.Redirect is used to redirect the user to another page or site.
Can you explain the difference between an ADO.NET Dataset and an ADO Recordset?

A DataSet can represent an entire relational database in memory, complete with tables, relations, and views.
A DataSet is designed to work without any continuing connection to the original data source.
Data in a DataSet is bulk-loaded, rather than being loaded on demand.
There's no concept of cursor types in a DataSet.
DataSets have no current record pointer You can use For Each loops to move through the data.
You can store many edits in a DataSet, and write them to the original data source in a single operation.
Though the DataSet is universal, other objects in ADO.NET come in different versions for different data sources.

Can you give an example of what might be best suited to place in the Application_Start and Session_Start subroutines? This is where you can set the specific variables for the Application and Session objects.
If I'm developing an application that must accommodate multiple security levels though secure login and my ASP.NET web application is spanned across three web-servers (using round-robin load balancing) what would be the best approach to maintain login-in state for the users? Maintain the login state security through a database.
Can you explain what inheritance is and an example of when you might use it? When you want to inherit (use the functionality of) another class. Base Class Employee. A Manager class could be derived from the Employee base class.
Whats an assembly? Assemblies are the building blocks of the .NET framework. Overview of assemblies from MSDN
Describe the difference between inline and code behind. Inline code written along side the html in a page. Code-behind is code written in a separate file and referenced by the .aspx page.
Explain what a diffgram is, and a good use for one? The DiffGram is one of the two XML formats that you can use to render DataSet object contents to XML. For reading database data to an XML file to be sent to a Web Service.
Whats MSIL, and why should my developers need an appreciation of it if at all? MSIL is the Microsoft Intermediate Language. All .NET compatible languages will get converted to MSIL.
Which method do you invoke on the DataAdapter control to load your generated dataset with data? The .Fill() method
Can you edit data in the Repeater control? No, it just reads the information from its data source
Which template must you provide, in order to display data in a Repeater control? ItemTemplate
How can you provide an alternating color scheme in a Repeater control? Use the AlternatingItemTemplate
What property must you set, and what method must you call in your code, in order to bind the data from some data source to the Repeater control? You must set the DataSource property and call the DataBind method.
What base class do all Web Forms inherit from? The Page class.
Name two properties common in every validation control? ControlToValidate property and Text property.
What tags do you need to add within the asp:datagrid tags to bind columns manually? Set AutoGenerateColumns Property to false on the datagrid tag
What tag do you use to add a hyperlink column to the DataGrid? <asp:HyperLinkColumn>
What is the transport protocol you use to call a Web service? SOAP is the preferred protocol.
True or False: A Web service can only be written in .NET? False
What does WSDL stand for? (Web Services Description Language)
Where on the Internet would you look for Web services? (http://www.uddi.org)
Which property on a Combo Box do you set with a column name, prior to setting the DataSource, to display data in the combo box? DataTextField property
Which control would you use if you needed to make sure the values in two different controls matched? CompareValidator Control
True or False: To test a Web service you must create a windows application or Web application to consume this service? False, the webservice comes with a test page and it provides HTTP-GET method to test.
How many classes can a single .NET DLL contain? It can contain many classes.

C# Interview Questions

2012-08-09T06:57:00.001-07:00

C# Interview Questions

1. What's the implicit name of the parameter that gets passed into the class' set method? Value, and its datatype depends on whatever variable we're changing.

2. How do you inherit from a class in C#? Place a colon and then the name of the base class. Notice that it's double colon in C++.

3. Does C# support multiple inheritance? No, use interfaces instead.

4. When you inherit a protected class-level variable, who is it available to? Classes in the same namespace.

5. Are private class-level variables inherited? Yes, but they are not accessible, so looking at it you can honestly say that they are not inherited. But they are.

6. Describe the accessibility modifier protected internal. It's available to derived classes and classes within the same Assembly (and naturally from the base class it's declared in).

7. C# provides a default constructor for me. I write a constructor that takes a string as a parameter, but want to keep the no parameter one. How many constructors should I write? Two. Once you write at least one constructor, C# cancels the freebie constructor, and now you have to write one yourself, even if there's no implementation in it.

8. What's the top .NET class that everything is derived from? System.Object.

9. How's method overriding different from overloading? When overriding, you change the method behavior for a derived class. Overloading simply involves having a method with the same name within the class.

10. What does the keyword virtual mean in the method definition? The method can be over-ridden.

11. Can you declare the override method static while the original method is non-static? No, you can't, the signature of the virtual method must remain the same, only the keyword virtual is changed to keyword override.

12. Can you override private virtual methods? No, moreover, you cannot access private methods in inherited classes, have to be protected in the base class to allow any sort of access.

13. Can you prevent your class from being inherited and becoming a base class for some other classes? Yes, that's what keyword sealed in the class definition is for. The developer trying to derive from your class will get a message: cannot inherit from Sealed class WhateverBaseClassName. It's the same concept as final class in Java.

14. Can you allow class to be inherited, but prevent the method from being over-ridden? Yes, just leave the class public and make the method sealed.

15. What's an abstract class? A class that cannot be instantiated. A concept in C++ known as pure virtual method. A class that must be inherited and have the methods over-ridden. Essentially, it's a blueprint for a class without any implementation.

16. When do you absolutely have to declare a class as abstract (as opposed to free-willed educated choice or decision based on UML diagram)? When at least one of the methods in the class is abstract. When the class itself is inherited from an abstract class, but not all base abstract methods have been over-ridden.

17. What's an interface class? It's an abstract class with public abstract methods all of which must be implemented in the inherited classes.

18. Why can't you specify the accessibility modifier for methods inside the interface? They all must be public. Therefore, to prevent you from getting the false impression that you have any freedom of choice, you are not allowed to specify any accessibility, it's public by default.

19. Can you inherit multiple interfaces? Yes, why not.

20. And if they have conflicting method names? It's up to you to implement the method inside your own class, so implementation is left entirely up to you. This might cause a problem on a higher-level scale if similarly named methods from different interfaces expect different data, but as far as compiler cares you're okay.

21. What's the difference between an interface and abstract class? In the interface all methods must be abstract; in the abstract class some methods can be concrete. In the interface no accessibility modifiers are allowed, which is ok in abstract classes.

22. How can you overload a method? Different parameter data types, different number of parameters, different order of parameters.

23. If a base class has a bunch of overloaded constructors, and an inherited class has another bunch of overloaded constructors, can you enforce a call from an inherited constructor to an arbitrary base constructor? Yes, just place a colon, and then keyword base (parameter list to invoke the appropriate constructor) in the overloaded constructor definition inside the inherited class.

24. What's the difference between System.String and System.StringBuilder classes? System.String is immutable; System.StringBuilder was designed with the purpose of having a mutable string where a variety of operations can be performed.

25. What's the advantage of using System.Text.StringBuilder over System.String? StringBuilder is more efficient in the cases, where a lot of manipulation is done to the text. Strings are immutable, so each time it's being operated on, a new instance is created.

26. Can you store multiple data types in System.Array? No.

27. What's the difference between the System.Array.CopyTo() and System.Array.Clone()? The first one performs a deep copy of the array, the second one is shallow.

28. How can you sort the elements of the array in descending order? By calling Sort() and then Reverse() methods.

29. What's the .NET datatype that allows the retrieval of data by a unique key? HashTable.

30. What's class SortedList underneath? A sorted HashTable.

31. Will finally block get executed if the exception had not occurred? Yes.

32. What's the C# equivalent of C++ catch (…), which was a catch-all statement for any possible exception? A catch block that catches the exception of type System.Exception. You can also omit the parameter data type in this case and just write catch {}.

33. Can multiple catch blocks be executed? No, once the proper catch code fires off, the control is transferred to the finally block (if there are any), and then whatever follows the finally block.

34. Why is it a bad idea to throw your own exceptions? Well, if at that point you know that an error has occurred, then why not write the proper code to handle that error instead of passing a new Exception object to the catch block? Throwing your own exceptions signifies some design flaws in the project.

35. What's a delegate? A delegate object encapsulates a reference to a method. In C++ they were referred to as function pointers.

36. What's a multicast delegate? It's a delegate that points to and eventually fires off several methods.

37. 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.

38. What are the ways to deploy an assembly? An MSI installer, a CAB archive, and XCOPY command.

39. What's a satellite assembly? When you write a multilingual or multi-cultural application in .NET, and want to distribute the core application separately from the localized modules, the localized assemblies that modify the core application are called satellite assemblies.

40. What namespaces are necessary to create a localized application? System.Globalization, System.Resources.

41. What's the difference between // comments, /* */ comments and /// comments? Single-line, multi-line and XML documentation comments.

42. How do you generate documentation from the C# file commented properly with a command-line compiler? Compile it with a /doc switch.

43. What's the difference between and XML documentation tag? Single line code example and multiple-line code example.

44. Is XML case-sensitive? Yes, so and are different elements.

45. What debugging tools come with the .NET SDK? CorDBG – command-line debugger, and DbgCLR – graphic debugger. Visual Studio .NET uses the DbgCLR. To use CorDbg, you must compile the original C# file using the /debug switch.

46. What does the This window show in the debugger? It points to the object that's pointed to by this reference. Object's instance data is shown.

47. What does assert() do? In debug compilation, assert takes in a Boolean condition as a parameter, and shows the error dialog if the condition is false. The program proceeds without any interruption if the condition is true.

48. What's the difference between the Debug class and Trace class? Documentation looks the same. Use Debug class for debug builds, use Trace class for both debug and release builds.

49. Why are there five tracing levels in System.Diagnostics.TraceSwitcher? The tracing dumps can be quite verbose and for some applications that are constantly running you run the risk of overloading the machine and the hard drive there. Five levels range from None to Verbose, allowing to fine-tune the tracing activities.

50. Where is the output of TextWriterTraceListener redirected? To the Console or a text file depending on the parameter passed to the constructor.

51. How do you debug an ASP.NET Web application? Attach the aspnet_wp.exe process to the DbgClr debugger.

52. What are three test cases you should go through in unit testing? Positive test cases (correct data, correct output), negative test cases (broken or missing data, proper handling), exception test cases (exceptions are thrown and caught properly).

53. Can you change the value of a variable while debugging a C# application? Yes, if you are debugging via Visual Studio.NET, just go to Immediate window.

54. Explain the three services model (three-tier application). Presentation (UI), business (logic and underlying code) and data (from storage or other sources).

55. What are advantages and disadvantages of Microsoft-provided data provider classes in ADO.NET? SQLServer.NET data provider is high-speed and robust, but requires SQL Server license purchased from Microsoft. OLE-DB.NET is universal for accessing other sources, like Oracle, DB2, Microsoft Access and Informix, but it's a .NET layer on top of OLE layer, so not the fastest thing in the world. ODBC.NET is a deprecated layer provided for backward compatibility to ODBC engines.

56. What's the role of the DataReader class in ADO.NET connections? It returns a read-only dataset from the data source when the command is executed.

57. What is the wildcard character in SQL? Let's say you want to query database with LIKE for all employees whose name starts with La. The wildcard character is %, the proper query with LIKE would involve 'La%'.

58. Explain ACID rule of thumb for transactions. Transaction must be Atomic (it is one unit of work and does not dependent on previous and following transactions), Consistent (data is either committed or roll back, no "in-between" case where something has been updated and something hasn't), Isolated (no transaction sees the intermediate results of the current transaction), Durable (the values persist if the data had been committed even if the system crashes right after).

59. What connections does Microsoft SQL Server support? Windows Authentication (via Active Directory) and SQL Server authentication (via Microsoft SQL Server username and passwords).

60. Which one is trusted and which one is untrusted? Windows Authentication is trusted because the username and password are checked with the Active Directory, the SQL Server authentication is untrusted, since SQL Server is the only verifier participating in the transaction.

61. Why would you use untrusted verificaion? Web Services might use it, as well as non-Windows applications.

62. What does the parameter Initial Catalog define inside Connection String? The database name to connect to.

63. What's the data provider name to connect to Access database? Microsoft.Access.

64. What does Dispose method do with the connection object? Deletes it from the memory.

65. What is a pre-requisite for connection pooling? Multiple processes must agree that they will share the same connection, where every parameter is the same, including the security settings.

66. What's the implicit name of the parameter that gets passed into the class' set method? Value, and it's datatype depends on whatever variable we're changing.

67. How do you inherit from a class in C#? Place a colon and then the name of the base class.

68. Does C# support multiple inheritance? No, use interfaces instead.

69. When you inherit a protected class-level variable, who is it available to?Classes in the same namespace.

70. Are private class-level variables inherited? Yes, but they are not accessible, so looking at it you can honestly say that they are not inherited. But they are.

71. Describe the accessibility modifier protected internal. It's available to derived classes and classes within the same Assembly (and naturally from the base class it's declared in).

72. C# provides a default constructor for me. I write a constructor that takes a string as a parameter, but want to keep the no parameter one. How many constructors should I write? Two. Once you write at least one constructor, C# cancels the freebie constructor, and now you have to write one yourself, even if there's no implementation in it.

73. What's the top .NET class that everything is derived from? System.Object.

74. How's method overriding different from overloading? When overriding, you change the method behavior for a derived class. Overloading simply involves having a method with the same name within the class.

75. What does the keyword virtual mean in the method definition? The method can be over-ridden.

76. Can you declare the override method static while the original method is non-static? No, you can't, the signature of the virtual method must remain the same, only the keyword virtual is changed to keyword override.

77. Can you override private virtual methods? No, moreover, you cannot access private methods in inherited classes, have to be protected in the base class to allow any sort of access.

78. Can you prevent your class from being inherited and becoming a base class for some other classes? Yes, that's what keyword sealed in the class definition is for. The developer trying to derive from your class will get a message: cannot inherit from Sealed class WhateverBaseClassName. It's the same concept as final class in Java.

79. Can you allow class to be inherited, but prevent the method from being over-ridden? Yes, just leave the class public and make the method sealed.

80. What's an abstract class? A class that cannot be instantiated. A concept in C++ known as pure virtual method. A class that must be inherited and have the methods over-ridden. Essentially, it's a blueprint for a class without any implementation.

81. When do you absolutely have to declare a class as abstract (as opposed to free-willed educated choice or decision based on UML diagram)? When at least one of the methods in the class is abstract. When the class itself is inherited from an abstract class, but not all base abstract methods have been over-ridden.

82. What's an interface class? It's an abstract class with public abstract methods all of which must be implemented in the inherited classes.

83. Why can't you specify the accessibility modifier for methods inside the interface? They all must be public. Therefore, to prevent you from getting the false impression that you have any freedom of choice, you are not allowed to specify any accessibility, it's public by default.

84. Can you inherit multiple interfaces? Yes, why not.

85. And if they have conflicting method names? It's up to you to implement the method inside your own class, so implementation is left entirely up to you. This might cause a problem on a higher-level scale if similarly named methods from different interfaces expect different data, but as far as compiler cares you're okay.

86. What's the difference between an interface and abstract class? In the interface all methods must be abstract, in the abstract class some methods can be concrete. In the interface no accessibility modifiers are allowed, which is ok in abstract classes.

87. How can you overload a method? Different parameter data types, different number of parameters, different order of parameters.

88. If a base class has a bunch of overloaded constructors, and an inherited class has another bunch of overloaded constructors, can you enforce a call from an inherited constructor to an arbitrary base constructor? Yes, just place a colon, and then keyword base (parameter list to invoke the appropriate constructor) in the overloaded constructor definition inside the inherited class.

89. What's the difference between System.String and System.StringBuilder classes? System.String is immutable, System.StringBuilder was designed with the purpose of having a mutable string where a variety of operations can be performed.

90. Is it namespace class or class namespace? The .NET class library is organized into namespaces. Each namespace contains a functionally related group of classes so natural namespace comes first.

General Questions
1.Does C# support multiple-inheritance?
No. But you can use Interfaces.

2.Where is a protected class-level variable available?
It is available to any sub-class derived from base class

3.Are private class-level variables inherited?
Yes, but they are not accessible.

4.Describe the accessibility modifier "protected internal".
It is available to classes that are within the same assembly and derived from the specified base class.

6.Which class is at the top of .NET class hierarchy?
System.Object.

7.What does the term immutable mean?
The data value may not be changed.
Note: The variable value may be changed, but the original immutable data value was discarded and a new data value was created in memory.

8.What's the difference between System.String and System.Text.StringBuilder classes?
System.String is immutable.
System.StringBuilder was designed with the purpose of having a mutable string where a variety of operations can be performed.

9.What's the advantage of using System.Text.StringBuilder over System.String?

StringBuilder is more efficient in cases where there is a large amount of string manipulation. Strings are immutable, so each time a string is changed, a new instance in memory is created.

10.Can you store multiple data types in System.Array?
No.

11.What's the difference between the System.Array.CopyTo() and System.Array.Clone()?
The Clone() method returns a new array (a shallow copy) object containing all the elements in the original array. The CopyTo() method copies the elements into another existing array. Both perform a shallow copy. A shallow copy means the contents (each array element) contains references to the same object as the elements in the original array. A deep copy (which neither of these methods performs) would create a new instance of each element's object, resulting in a different, yet identacle object.

12.How can you sort the elements of the array in descending order?
By calling Sort() and then Reverse() methods.

13.What's the .NET collection class that allows an element to be accessed using a unique key?
HashTable.

14.What class is underneath the SortedList class?
A sorted HashTable.

15.Will the finally block get executed if an exception has not occurred?
Yes.

16.What's the C# syntax to catch any possible exception?
A catch block that catches the exception of type System.Exception. You can also omit the parameter data type in this case and just write catch {}.

17.Can multiple catch blocks be executed for a single try statement?
No. Once the proper catch block processed, control is transferred to the finally block .

18.Explain the three services model commonly know as a three-tier application?
Presentation (UI), Business (logic and underlying code) and Data (from storage or other sources).

Class Questions
1.What is the syntax to inherit from a class in C#?
Place a colon and then the name of the base class.
Example: class MyNewClass : MyBaseClass

2.Can you prevent your class from being inherited by another class?
Yes. The keyword "sealed" will prevent the class from being inherited.

3.Can you allow a class to be inherited, but prevent the method from being over-ridden?
Yes. Just leave the class public and make the method sealed.

4.What's an abstract class?
A class that cannot be instantiated. An abstract class is a class that must be inherited and have the methods overridden. An abstract class is essentially a blueprint for a class without any implementation.

5.When do you absolutely have to declare a class as abstract?

1. When the class itself is inherited from an abstract class, but not all base abstract methods have been overridden.

2. When at least one of the methods in the class is abstract.

6.What is an interface class?
Interfaces, like classes, define a set of properties, methods, and events. But unlike classes, interfaces do not provide implementation. They are implemented by classes, and defined as separate entities from classes.

7.Why can't you specify the accessibility modifier for methods inside the interface?
They all must be public, and are therefore public by default.

8.Can you inherit multiple interfaces?
Yes. .NET does support multiple interfaces.

9.What happens if you inherit multiple interfaces and they have conflicting method names?
It's up to you to implement the method inside your own class, so implementation is left entirely up to you. This might cause a problem on a higher-level scale if similarly named methods from different interfaces expect different data, but as far as compiler cares you're okay.

10. What's the difference between an interface and abstract class?
In an interface class, all methods are abstract - there is no implementation. In an abstract class some methods can be concrete. In an interface class, no accessibility modifiers are allowed. An abstract class may have accessibility modifiers.

11. What is the difference between a Struct and a Class?
Structs are value-type variables and are thus saved on the stack, additional overhead but faster retrieval. Another difference is that structs cannot inherit.

Method and Property Questions

1. What's the implicit name of the parameter that gets passed into the set method/property of a class?
Value. The data type of the value parameter is defined by whatever data type the property is declared .

2. What does the keyword "virtual" declare for a method or property?
The method or property can be overridden.

3. How is method overriding different from method overloading?
When overriding a method, you change the behavior of the method for the derived class. Overloading a method simply involves having another method with the same name within the class.

4. Can you declare an override method to be static if the original method is not static?
No. The signature of the virtual method must remain the same. (Note: Only the keyword virtual is changed to keyword override)

5. What are the different ways a method can be overloaded?
Different parameter data types, different number of parameters, different order of parameters.

6. If a base class has a number of overloaded constructors, and an inheriting class has a number of overloaded constructors; can you enforce a call from an inherited constructor to a specific base constructor?
Yes, just place a colon, and then keyword base (parameter list to invoke the appropriate constructor) in the overloaded constructor definition inside the inherited class.

Events and Delegates
1. What's a delegate?
A delegate object encapsulates a reference to a method.

2. What's a multicast delegate?
A delegate that has multiple handlers assigned to it. Each assigned handler (method) is called.

3. What's the implicit name of the parameter that gets passed into the class' set method?
Value, and it's datatype depends on whatever variable we're changing.

4. How do you inherit from a class in C#?
Place a colon and then the name of the base class.

5. Does C# support multiple inheritance?
No, use interfaces instead.

6. When you inherit a protected class-level variable, who is it available to?
Classes in the same namespace.

7. Are private class-level variables inherited?
Yes, but they are not accessible, so looking at it you can honestly say that they are not inherited.

8. Describe the accessibility modifier protected internal.?
It's available to derived classes and classes within the same Assembly (and naturally from the base class it's declared in).

9. C# provides a default constructor for me. I write a constructor that takes a string as a parameter, but want to keep the no parameter one. How many constructors should I write?
Two. Once you write at least one constructor, C# cancels the freebie constructor, and now you have to write one yourself, even if there's no implementation in it.

10. What's the top .NET class that everything is derived from?
System.Object.

11. How's method overriding different from overloading?
When overriding, you change the method behavior for a derived class. Overloading simply involves having a method with the same name within the class.

12. What does the keyword virtual mean in the method definition?
The method can be over-ridden.

13. Can you declare the override method static while the original method is non-static?
No, you can't, the signature of the virtual method must remain the same, only the keyword virtual is changed to keyword override.

14. Can you override private virtual methods?
No, moreover, you cannot access private methods in inherited classes, have to be protected in the base class to allow any sort of access.

15. Can you prevent your class from being inherited and becoming a base class for some other classes?
Yes, that's what keyword sealed in the class definition is for. The developer trying to derive from your class will get a message: cannot inherit from Sealed class WhateverBaseClassName.
It's the same concept as final class in Java.

16. Can you allow class to be inherited, but prevent the method from being over-ridden?
Yes, just leave the class public and make the method sealed.

17. What's an abstract class?
A class that cannot be instantiated. A concept in C++ known as pure virtual method. A class that must be inherited and have the methods over-ridden.
Essentially, it's a blueprint for a class without any implementation.

18. When do you absolutely have to declare a class as abstract (as opposed to free-willed educated choice or decision based on UML diagram)?
When at least one of the methods in the class is abstract. When the class itself is inherited from an abstract class, but not all base abstract methods have been over-ridden.

19. What's an interface class?
It's an abstract class with public abstract methods all of which must be implemented in the inherited classes.

20. Why can't you specify the accessibility modifier for methods inside the interface?
They all must be public. Therefore, to prevent you from getting the false impression that you have any freedom of choice, you are not allowed to specify any accessibility, it's public by default.

21. Can you inherit multiple interfaces?
Yes, why not.

22. And if they have conflicting method names?
It's up to you to implement the method inside your own class, so implementation is left entirely up to you.
This might cause a problem on a higher-level scale if similarly named methods from different interfaces expect different data, but as far as compiler cares you're okay.

23. What's the difference between an interface and abstract class?
In the interface all methods must be abstract, in the abstract class some methods can be concrete. In the interface no accessibility modifiers are allowed, which is ok in abstract classes.

24. How can you overload a method?
Different parameter data types, different number of parameters, different order of parameters.

25. If a base class has a bunch of overloaded constructors, and an inherited class has another bunch of overloaded constructors, can you enforce a call from an inherited constructor to an arbitrary base constructor?
Yes, just place a colon, and then keyword base (parameter list to invoke the appropriate constructor) in the overloaded constructor definition inside the inherited class.

26. What's the difference between System.String and System.StringBuilder classes?
System.String is immutable, System.StringBuilder was designed with the purpose of having a mutable string where a variety of operations can be performed.

27. Is it namespace class or class namespace?
The .NET class library is organized into namespaces. Each namespace contains a functionally related group of classes so natural namespace comes first.