SET-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.
- 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.
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- 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. 0
- 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. Clone() just implements the ICloneable interface. It creates new instance of array holding the same elements, but returns object you have to cast.
ArrayCopy() is static helper method. It copies elements from one array to another. The destination array has to be already created with right dimension. You can use this method instead for loop.
- 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 <c> and <code> XML documentation tag?
Single line code example and multiple-line code example.
- Is XML case-sensitive?
Yes, so <Student> and <student> 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.
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SET-2
Q: Is the Try-Catch-Finally block available in C# as well?
A: Yes, the Try-Catch-Finally block is available in both VB.NET and C#.
Q: Can I use both structured and unstructured error handling within a function/ subroutine?
A: No, you cannot use both error handling mechanisms at the same time. It is
Q: When I try to run my ASP.NET application in VS.NET, I encounter this error message “Error while trying to run project: Unable to start debugging on the Web server.The project is not configured to be debugged.”Why does this occur?
A: This is caused by the setting of the debug attribute within the <compilation> element. During development stage, set the value of the debug attribute to “true.” Remember, however, to set this attribute to “false” when you are ready to deploy your application.
Q: I noticed during tracing that the Session ID for my application changes when I refresh my page or when I do a postback.Why is this happening?
A: For performance reasons, the .NET Framework does not maintain state between the Web server and the Web browser automatically, hence the Session ID is always different between submissions. However, when the Session object is used or when the Session_OnStart() event is added to the global.asax file, the Session ID would be maintained between postbacks.
Frequently Asked Questions(Web Services)
Q: Why replace COM objects with Web Services?
A: Web Services have a platform neutral interface.This enables Web Services to be easily utilized by multiple clients on different platforms developed with different programming languages. Note that existing COM components can be wrapped by Web Services.
Q: Can I create access to Web Services from a standard ASP page?
A: Yes, you can; however, you might want to look into Microsoft’s SOAP toolkit.
Q: How do I know I need Web Services?
A: If you have data that is needed by various customers (different departments, different levels of management, vendors, industry partners, consumers and so on) and getting to that data is hindered or prevented by issues involving platform, programming language, legacy hardware or other types of incompatibility, developing Web Services can help.
Q: What area of development are Web Services best for?
A: I believe that Web Services development like COM development will remain in the hands of the middle tier programmer.Traditionally this was accomplished with C++ and VB programmers, however simple data access type components may be developed by intermediate and advanced ASP developers. While this might still be the case,ASP.NET developers need a firmer grasp of programming with a strongly typed compiled language then their ASP predecessors.This makes the ASP.NET developer more of a middle tier programmer and less of a front-end Web developer. Since building and deploying Web classes and Web Services are relatively easy with VS.NET as compared to traditional COM development. I think the proportion of components built by the ASP developer (using ASP.NET) will be larger than it has been in the past.
Q: Is it possible to try out Web Services using only my local computer?
A: Yes, it is. Using the WSDL.exe command line tool, you can point to any Web server.This is even easier with the VS.NET UI. Simply right-click Web references , then select any Web service from the UDDI directory or your local machine, or simply type the URL of a disco file on any server.You can easily generate a WSDL proxy and use it as long as you are connected to the Internet.
Q: I’m currently in the process of migrating.What considerations should I take with my existing COM components?
A: Here are a few things to consider:
_ Who is the customer? If the customer is only within the intranet and there are no external customers in the foreseeable future, an existing DCOM infrastructure needn’t be changed.
_ What type of clients do I have? If the client is a desktop application, switching to Web Services would require updating the client, which may include updating the OS, and possibly the hardware so that the client has enough memory to host the .NET Framework.
_ Will I need to support Mobile devices in the near future? Using the .NET Mobile Framework to access Web Services is as simple as it is with .NET. Updating the existing clients to .NET will make adding future clients simple and cost-effective.
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