الخميس، 19 يناير، 2012

.Net Interview Questions .

C#, ASP.NET, .NET Remoting, .NET Windows Forms



Interview Questions

C#



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.



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++.



Does C# support multiple inheritance?

No, use interfaces instead.



When you inherit a protected class-level variable, who is it available to?

Classes in the same namespace.



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.



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).



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.



What’s the top .NET class that everything is derived from?

System.Object.



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.



What does the keyword virtual mean in the method definition?

The method can be over-ridden.



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.



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.



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.



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.



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.



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.



What’s an interface class?

It’s an abstract class with public abstract methods all of which must be implemented in the inherited classes.



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.



Can you inherit multiple interfaces?

Yes, why not.



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.



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.



How can you overload a method?

Different parameter data types, different number of parameters, different order of parameters.



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.



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.



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.



Can you store multiple data types in System.Array?

No.



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.



How can you sort the elements of the array in descending order?

By calling Sort() and then Reverse() methods.



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

HashTable.



What’s class SortedList underneath?

A sorted HashTable.



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

Yes.



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 {}.



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.



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.



What’s a delegate?

A delegate object encapsulates a reference to a method. In C++ they were referred to as function pointers.



What’s a multicast delegate?

It’s a delegate that points to and eventually fires off several methods.



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.



What are the ways to deploy an assembly?

An MSI installer, a CAB archive, and XCOPY command.



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.



What namespaces are necessary to create a localized application?

System.Globalization, System.Resources.



What’s the difference between // comments, /* */ comments and /// comments?

Single-line, multi-line and XML documentation comments.



How do you generate documentation from the C# file commented properly with a command-line compiler?

Compile it with a /doc switch.



What’s the difference between and XML documentation tag?

Single line code example and multiple-line code example.



Is XML case-sensitive?

Yes, so and are different elements.



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.



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.



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.



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.



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.



Where is the output of TextWriterTraceListener redirected?

To the Console or a text file depending on the parameter passed to the constructor.



How do you debug an ASP.NET Web application?

Attach the aspnet_wp.exe process to the DbgClr debugger.



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).



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.



Explain the three services model (three-tier application).

Presentation (UI), business (logic and underlying code) and data (from storage or other sources).



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.



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.



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%’.



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).



What connections does Microsoft SQL Server support?

Windows Authentication (via Active Directory) and SQL Server authentication (via Microsoft SQL Server username and passwords).



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.



Why would you use untrusted verificaion?

Web Services might use it, as well as non-Windows applications.



What does the parameter Initial Catalog define inside Connection String?

The database name to connect to.



What’s the data provider name to connect to Access database?

Microsoft.Access.



What does Dispose method do with the connection object?

Deletes it from the memory.



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.



Interview Questions

ASP.NET



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?





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.









Interview Questions

.NET Remoting





What’s a Windows process?

It’s an application that’s running and had been allocated memory.



What’s typical about a Windows process in regards to memory allocation?

Each process is allocated its own block of available RAM space, no process can access another process’ code or data. If the process crashes, it dies alone without taking the entire OS or a bunch of other applications down.



Why do you call it a process? What’s different between process and application in .NET, not common computer usage, terminology?

A process is an instance of a running application. An application is an executable on the hard drive or network. There can be numerous processes launched of the same application (5 copies of Word running), but 1 process can run just 1 application.



What distributed process frameworks outside .NET do you know?

Distributed Computing Environment/Remote Procedure Calls (DEC/RPC), Microsoft Distributed Component Object Model (DCOM), Common Object Request Broker Architecture (CORBA), and Java Remote Method Invocation (RMI).



What are possible implementations of distributed applications in .NET?

.NET Remoting and ASP.NET Web Services. If we talk about the Framework Class Library, noteworthy classes are in System.Runtime.Remoting and System.Web.Services.



When would you use .NET Remoting and when Web services?

Use remoting for more efficient exchange of information when you control both ends of the application. Use Web services for open-protocol-based information exchange when you are just a client or a server with the other end belonging to someone else.



What’s a proxy of the server object in .NET Remoting?

It’s a fake copy of the server object that resides on the client side and behaves as if it was the server. It handles the communication between real server object and the client object. This process is also known as marshaling.



What are remotable objects in .NET Remoting?

Remotable objects are the objects that can be marshaled across the application domains. You can marshal by value, where a deep copy of the object is created and then passed to the receiver. You can also marshal by reference, where just a reference to an existing object is passed.



What are channels in .NET Remoting?

Channels represent the objects that transfer the other serialized objects from one application domain to another and from one computer to another, as well as one process to another on the same box. A channel must exist before an object can be transferred.



What security measures exist for .NET Remoting in System.Runtime.Remoting?

None. Security should be taken care of at the application level. Cryptography and other security techniques can be applied at application or server level.



What is a formatter?

A formatter is an object that is responsible for encoding and serializing data into messages on one end, and deserializing and decoding messages into data on the other end.



Choosing between HTTP and TCP for protocols and Binary and SOAP for formatters, what are the trade-offs?

Binary over TCP is the most effiecient, SOAP over HTTP is the most interoperable.



What’s SingleCall activation mode used for?

If the server object is instantiated for responding to just one single request, the request should be made in SingleCall mode.



What’s Singleton activation mode?

A single object is instantiated regardless of the number of clients accessing it. Lifetime of this object is determined by lifetime lease.



How do you define the lease of the object?

By implementing ILease interface when writing the class code.



Can you configure a .NET Remoting object via XML file?

Yes, via machine.config and application level .config file (or web.config in ASP.NET). Application-level XML settings take precedence over machine.config.



How can you automatically generate interface for the remotable object in .NET with Microsoft tools?

Use the Soapsuds tool.







Interview Questions

.NET Windows Forms



Write a simple Windows Forms MessageBox statement.

System.Windows.Forms.MessageBox.Show

("Hello, Windows Forms");



Can you write a class without specifying namespace? Which namespace does it belong to by default??

Yes, you can, then the class belongs to global namespace which has no name. For commercial products, naturally, you wouldn’t want global namespace.



You are designing a GUI application with a window and several widgets on it. The user then resizes the app window and sees a lot of grey space, while the widgets stay in place. What’s the problem?

One should use anchoring for correct resizing. Otherwise the default property of a widget on a form is top-left, so it stays at the same location when resized.



How can you save the desired properties of Windows Forms application?

.config files in .NET are supported through the API to allow storing and retrieving information. They are nothing more than simple XML files, sort of like what .ini files were before for Win32 apps.



So how do you retrieve the customized properties of a .NET application from XML .config file?

Initialize an instance of AppSettingsReader class. Call the GetValue method of AppSettingsReader class, passing in the name of the property and the type expected. Assign the result to the appropriate variable.



Can you automate this process?

In Visual Studio yes, use Dynamic Properties for automatic .config creation, storage and retrieval.



My progress bar freezes up and dialog window shows blank, when an intensive background process takes over.

Yes, you should’ve multi-threaded your GUI, with taskbar and main form being one thread, and the background process being the other.



What’s the safest way to deploy a Windows Forms app?

Web deployment: the user always downloads the latest version of the code; the program runs within security sandbox, properly written app will not require additional security privileges.



Why is it not a good idea to insert code into InitializeComponent method when working with Visual Studio?

The designer will likely throw it away; most of the code inside InitializeComponent is auto-generated.



What’s the difference between WindowsDefaultLocation and WindowsDefaultBounds?

WindowsDefaultLocation tells the form to start up at a location selected by OS, but with internally specified size. WindowsDefaultBounds delegates both size and starting position choices to the OS.



What’s the difference between Move and LocationChanged? Resize and SizeChanged?

Both methods do the same, Move and Resize are the names adopted from VB to ease migration to C#.



How would you create a non-rectangular window, let’s say an ellipse?

Create a rectangular form, set the TransparencyKey property to the same value as BackColor, which will effectively make the background of the form transparent. Then set the FormBorderStyle to FormBorderStyle.None, which will remove the contour and contents of the form.



How do you create a separator in the Menu Designer?

A hyphen ‘-’ would do it. Also, an ampersand ‘&\’ would underline the next letter.



How’s anchoring different from docking?

Anchoring treats the component as having the absolute size and adjusts its location relative to the parent form. Docking treats the component location as absolute and disregards the component size. So if a status bar must always be at the bottom no matter what, use docking. If a button should be on the top right, but change its position with the form being resized, use anchorin

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