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C# Interview Questions and Answers


From a versioning perspective, what are the drawbacks of extending an interface as opposed to extending a class?
With regard to versioning, interfaces are less flexible than classes. With a class, you can ship version 1 and then, in version 2, decide to add another method. As long as the method is not abstract (i.e., as long as you provide a default implementation of the method), any existing derived classes continue to function with no changes. Because interfaces do not support implementation inheritance, this same pattern does not hold for interfaces. Adding a method to an interface is like adding an abstract method to a base class--any class that implements the interface will break, because the class doesn't implement the new interface method. 

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

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

Does Console.WriteLine() stop printing when it reaches a NULL character within a string?
Strings are not null terminated in the runtime, so embedded nulls are allowed. Console.WriteLine() and all similar methods continue until the end of the string.

What is 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 is being operated on, a new instance is created.

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 is 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.

Why do I get a security exception when I try to run my C# app?
Some security exceptions are thrown if you are working on a network share. There are some parts of the frameworks that will not run if being run off a share (roaming profile, mapped drives, etc.). To see if this is what's happening, just move the executable over to your local drive and see if it runs without the exceptions. One of the common exceptions thrown under these conditions is
To get around this, you can change your security policy for the intranet zone, code group 1.2, (the zone that running off shared folders falls into) by using the caspol.exe tool.

Is there any sample C# code for simple threading?
Some sample code follows: using System;
using System.Threading;
class ThreadTest
public void runme()
Console.WriteLine("Runme Called");
public static void Main(String[] args)
ThreadTest b = new ThreadTest();
Thread t = new Thread(new ThreadStart(b.runme));

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

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

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

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).

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

How do I port "synchronized" functions from Visual J++ to C#?
Original Visual J++ code: public synchronized void Run()
// function body
Ported C# code: class C
public void Run()
// function body
public static void Main() {}

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