1. What is the transport protocol you use to call a Web service?
SOAP (Simple Object Access Protocol) is the preferred protocol.
2. True or False: A Web service can only be written in .NET?
False
3. What does WSDL stand for?
Web Services Description Language.
4. Where on the Internet would you look for Web services?
http://www.uddi.org
5. True or False: To test a Web service you must create a Windows application or Web application to consume this service?
False, the web service comes with a test page and it provides HTTP-GET method to test.
State Management Questions
1. What is ViewState?
ViewState allows the state of objects (serializable) to be stored in a hidden field on the page. ViewState is transported to the client and back to the server, and is not stored on the server or any other external source. ViewState is used the retain the state of server-side objects between postabacks.
2. What is the lifespan for items stored in ViewState?
Item stored in ViewState exist for the life of the current page. This includes postbacks (to the same page).
3. What does the "EnableViewState" property do? Why would I want it on or off?
It allows the page to save the users input on a form across postbacks. It saves the server-side values for a given control into ViewState, which is stored as a hidden value on the page before sending the page to the clients browser. When the page is posted back to the server the server control is recreated with the state stored in viewstate.
4. What are the different types of Session state management options available with ASP.NET?
ASP.NET provides In-Process and Out-of-Process state management. In-Process stores the session in memory on the web server. This requires the a "sticky-server" (or no load-balancing) so that the user is always reconnected to the same web server. Out-of-Process Session state management stores data in an external data source. The external data source may be either a SQL Server or a State Server service. Out-of-Process state management requires that all objects stored in session are serializable.
.NET Remoting Interview Questions
To Do: Comfirm these are correct answers. Many of these question I have obtained from other sources and have found they are not entirely correct, or simply wrong.
1. What’s a Windows process?
It’s an application that’s running and had been allocated memory.
2. 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.
3. Explain what relationship is between a Process, Application Domain, and Application?
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.
4. 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.
5. What are the consideration in deciding to use .NET Remoting or ASP.NET Web Services?
Remoting is a more efficient communication exchange when you can control both ends of the application involved in the communication process. Web Services provide an open-protocol-based exchange of informaion. Web Services are best when you need to communicate with an external organization or another (non-.NET) technology.
6. 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.
7. 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.
8. 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.
9. 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.
10. 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.
11. 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.
12. 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.
13. 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.
14. How do you define the lease of the object?
By implementing ILease interface when writing the class code.
15. 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.
16. How can you automatically generate interface for the remotable object in .NET with Microsoft tools?
Use the Soapsuds tool.
C# Interview Questions
This is a list of questions I have gathered from other sources and created myself over a period of time from my experience, many of which I felt where incomplete or simply wrong. I have finally taken the time to go through each question and correct them to the best of my ability. However, please feel free to post feedback to challenge, improve, or suggest new questions. I want to thank those of you that have contributed quality questions and corrections thus far.
There are some question in this list that I do not consider to be good questions for an interview. However, they do exist on other lists available on the Internet so I felt compelled to keep them easy access.
General Questions
1. Does C# support multiple-inheritance?
No.
2. Who is a protected class-level variable available to?
It is available to any sub-class (a class inheriting this class).
3. Are private class-level variables inherited?
Yes, but they are not accessible. Although they are not visible or accessible via the class interface, they are inherited.
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.
5. What’s the top .NET class that everything is derived from?
System.Object.
6. 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.
7. 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.
8. 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.
9. Can you store multiple data types in System.Array?
No.
10. 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.
11. How can you sort the elements of the array in descending order?
By calling Sort() and then Reverse() methods.
12. What’s the .NET collection class that allows an element to be accessed using a unique key?
HashTable.
13. What class is underneath the SortedList class?
A sorted HashTable.
14. Will the finally block get executed if an exception has not occurred?-
Yes.
15. 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 {}.
16. 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 (if there are any).
17. 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.
To Do: Investigate
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 as.
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.
XML Documentation Questions
1. Is XML case-sensitive?
Yes.
2. What’s the difference between // comments, /* */ comments and /// comments?
Single-line comments, multi-line comments, and XML documentation comments.
3. How do you generate documentation from the C# file commented properly with a command-line compiler?
Compile it with the /doc switch.
Debugging and Testing Questions
1. What debugging tools come with the .NET SDK?
1. CorDBG – command-line debugger. To use CorDbg, you must compile the original C# file using the /debug switch.
2. DbgCLR – graphic debugger. Visual Studio .NET uses the DbgCLR.
2. What does assert() method 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.
3. 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.
4. Why are there five tracing levels in System.Diagnostics.TraceSwitcher?
The tracing dumps can be quite verbose. For applications that are constantly running you run the risk of overloading the machine and the hard drive. Five levels range from None to Verbose, allowing you to fine-tune the tracing activities.
5. Where is the output of TextWriterTraceListener redirected?
To the Console or a text file depending on the parameter passed to the constructor.
6. How do you debug an ASP.NET Web application?
Attach the aspnet_wp.exe process to the DbgClr debugger.
7. What are three test cases you should go through in unit testing?
1. Positive test cases (correct data, correct output).
2. Negative test cases (broken or missing data, proper handling).
3. Exception test cases (exceptions are thrown and caught properly).
8. 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.
ADO.NET and Database Questions
1. What is the role of the DataReader class in ADO.NET connections?
It returns a read-only, forward-only rowset from the data source. A DataReader provides fast access when a forward-only sequential read is needed.
2. 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. OLE-DB.NET is a .NET layer on top of the OLE layer, so it’s not as fastest and efficient as SqlServer.NET.
3. 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%’.
4. Explain ACID rule of thumb for transactions.
A transaction must be:
1. Atomic - it is one unit of work and does not dependent on previous and following transactions.
2. Consistent - data is either committed or roll back, no “in-between” case where something has been updated and something hasn’t.
3. Isolated - no transaction sees the intermediate results of the current transaction).
4. Durable - the values persist if the data had been committed even if the system crashes right after.
5. What connections does Microsoft SQL Server support?
Windows Authentication (via Active Directory) and SQL Server authentication (via Microsoft SQL Server username and password).
6. Between Windows Authentication and SQL Server Authentication, 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.
7. What does the Initial Catalog parameter define in the connection string?
The database name to connect to.
8. What does the Dispose method do with the connection object?
Deletes it from the memory.
To Do: answer better. The current answer is not entirely correct.
9. 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. The connection string must be identical.
Assembly Questions
1. How is 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.
2. What are the ways to deploy an assembly?
An MSI installer, a CAB archive, and XCOPY command.
3. What is 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.
4. What namespaces are necessary to create a localized application?
System.Globalization and System.Resources.
5. What is the smallest unit of execution in .NET?
an Assembly.
6. When should you call the garbage collector in .NET?
As a good rule, you should not call the garbage collector. However, you could call the garbage collector when you are done using a large object (or set of objects) to force the garbage collector to dispose of those very large objects from memory. However, this is usually not a good practice.
7. How do you convert a value-type to a reference-type?
Use Boxing.
8. What happens in memory when you Box and Unbox a value-type?
Boxing converts a value-type to a reference-type, thus storing the object on the heap. Unboxing converts a reference-type to a value-type, thus storing the value on the stack.
Interview questions for C# developers
Useful for preparation, but too specific to be used in the interview.
1. Is it possible to inline assembly or IL in C# code? - No.
2. Is it possible to have different access modifiers on the get/set methods of a property? - No. The access modifier on a property applies to both its get and set accessors. What you need to do if you want them to be different is make the property read-only (by only providing a get accessor) and create a private/internal set method that is separate from the property.
3. Is it possible to have a static indexer in C#? - No. Static indexers are not allowed in C#.
4. If I return out of a try/finally in C#, does the code in the finally-clause run? - Yes. The code in the finally always runs. If you return out of the try block, or even if you do a “goto” out of the try, the finally block always runs:
5. using System;
6.
7. class main
8. {
9. public static void Main()
10. {
11. try
12. {
13. Console.WriteLine("In Try block");
14. return;
15. }
16. finally
17. {
18. Console.WriteLine("In Finally block");
19. }
20. }
}
Both “In Try block” and “In Finally block” will be displayed. Whether the return is in the try block or after the try-finally block, performance is not affected either way. The compiler treats it as if the return were outside the try block anyway. If it’s a return without an expression (as it is above), the IL emitted is identical whether the return is inside or outside of the try. If the return has an expression, there’s an extra store/load of the value of the expression (since it has to be computed within the try block).
21. I was trying to use an “out int” parameter in one of my functions. How should I declare the variable that I am passing to it? - You should declare the variable as an int, but when you pass it in you must specify it as ‘out’, like the following: int i; foo(out i); where foo is declared as follows: [return-type] foo(out int o) { }
22. How does one compare strings in C#? - In the past, you had to call .ToString() on the strings when using the == or != operators to compare the strings’ values. That will still work, but the C# compiler now automatically compares the values instead of the references when the == or != operators are used on string types. If you actually do want to compare references, it can be done as follows: if ((object) str1 == (object) str2) { … } Here’s an example showing how string compares work:
23. using System;
24. public class StringTest
25. {
26. public static void Main(string[] args)
27. {
28. Object nullObj = null; Object realObj = new StringTest();
29. int i = 10;
30. Console.WriteLine("Null Object is [" + nullObj + "]n"
31. + "Real Object is [" + realObj + "]n"
32. + "i is [" + i + "]n");
33. // Show string equality operators
34. string str1 = "foo";
35. string str2 = "bar";
36. string str3 = "bar";
37. Console.WriteLine("{0} == {1} ? {2}", str1, str2, str1 == str2 );
38. Console.WriteLine("{0} == {1} ? {2}", str2, str3, str2 == str3 );
39. }
40. }
Output:
Null Object is []
Real Object is [StringTest]
i is [10]
foo == bar ? False
bar == bar ? True
41. How do you specify a custom attribute for the entire assembly (rather than for a class)? - Global attributes must appear after any top-level using clauses and before the first type or namespace declarations. An example of this is as follows:
42. using System;
43. [assembly : MyAttributeClass] class X {}
Note that in an IDE-created project, by convention, these attributes are placed in AssemblyInfo.cs.
44. How do you mark a method obsolete? -
[Obsolete] public int Foo() {...}
or
[Obsolete("This is a message describing why this method is obsolete")] public int Foo() {...}
Note: The O in Obsolete is always capitalized.
45. How do you implement thread synchronization (Object.Wait, Notify,and CriticalSection) in C#? - You want the lock statement, which is the same as Monitor Enter/Exit:
46. lock(obj) { // code }
translates to
try {
CriticalSection.Enter(obj);
// code
}
finally
{
CriticalSection.Exit(obj);
}
47. How do you directly call a native function exported from a DLL? - Here’s a quick example of the DllImport attribute in action:
48. using System.Runtime.InteropServices;
49. class C
50. {
51. [DllImport("user32.dll")]
52. public static extern int MessageBoxA(int h, string m, string c, int type);
53. public static int Main()
54. {
55. return MessageBoxA(0, "Hello World!", "Caption", 0);
56. }
57. }
This example shows the minimum requirements for declaring a C# method that is implemented in a native DLL. The method C.MessageBoxA() is declared with the static and external modifiers, and has the DllImport attribute, which tells the compiler that the implementation comes from the user32.dll, using the default name of MessageBoxA. For more information, look at the Platform Invoke tutorial in the documentation.
58. How do I simulate optional parameters to COM calls? - You must use the Missing class and pass Missing.Value (in System.Reflection) for any values that have optional parameters.
Dot.NET/C#/VB.NET/ASP.NET Interview Questions
1. Does C# support multiple inheritance?
No, use interfaces instead
2. 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
3. What’s the top .NET class that everything is derived from?
System.Object.
4. 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.
5. What is CLR?
The .NET Framework provides a runtime environment called the Common Language Runtime or CLR (similar to the Java Virtual Machine or JVM in Java), which handles the execution of code and provides useful services for the implementation of the program. CLR takes care of code management at program execution and provides various beneficial services such as memory management, thread management, security management, code verification, compilation, and other system services. The managed code that targets CLR benefits from useful features such as cross-language integration, cross-language exception handling, versioning, enhanced security, deployment support, and debugging.
6. What is CTS?
Common Type System (CTS) describes how types are declared, used and managed in the runtime and facilitates cross-language integration, type safety, and high performance code execution.
7. What is CLS?
The CLS is simply a specification that defines the rules to support language integration in such a way that programs written in any language, yet can interoperate with one another, taking full advantage of inheritance, polymorphism, exceptions, and other features. These rules and the specification are documented in the ECMA proposed standard document, "Partition I Architecture", http://msdn.microsoft.com/net/ecma
8. What is strong name?
A name that consists of an assembly's identity—its simple text name, version number, and culture information (if provided)—strengthened by a public key and a digital signature generated over the assembly.
9. What is Application Domain?
The primary purpose of the AppDomain is to isolate an application from other applications. Win32 processes provide isolation by having distinct memory address spaces. This is effective, but it is expensive and doesn't scale well. The .NET runtime enforces AppDomain isolation by keeping control over the use of memory - all memory in the AppDomain is managed by the .NET runtime, so the runtime can ensure that AppDomains do not access each other's memory. Objects in different application domains communicate either by transporting copies of objects across application domain boundaries, or by using a proxy to exchange messages.
10. What is serialization in .NET? What are the ways to control serialization?
Serialization is the process of converting an object into a stream of bytes. Deserialization is the opposite process of creating an object from a stream of bytes. Serialization/Deserialization is mostly used to transport objects (e.g. during remoting), or to persist objects (e.g. to a file or database).Serialization can be defined as the process of storing the state of an object to a storage medium. During this process, the public and private fields of the object and the name of the class, including the assembly containing the class, are converted to a stream of bytes, which is then written to a data stream. When the object is subsequently deserialized, an exact clone of the original object is created. Binary serialization preserves type fidelity, which is useful for preserving the state of an object between different invocations of an application. For example, you can share an object between different applications by serializing it to the clipboard. You can serialize an object to a stream, disk, memory, over the network, and so forth. Remoting uses serialization to pass objects "by value" from one computer or application domain to another. XML serialization serializes only public properties and fields and does not preserve type fidelity. This is useful when you want to provide or consume data without restricting the application that uses the data. Because XML is an open standard, it is an attractive choice for sharing data across the Web. SOAP is an open standard, which makes it an attractive choice. There are two separate mechanisms provided by the .NET class library - XmlSerializer and SoapFormatter/BinaryFormatter. Microsoft uses XmlSerializer for Web Services, and uses SoapFormatter/BinaryFormatter for remoting. Both are available for use in your own code.
11. What are Satellite Assemblies?
Satellite assemblies are often used to deploy language-specific resources for an application. These language-specific assemblies work in side-by-side execution because the application has a separate product ID for each language and installs satellite assemblies in a language-specific subdirectory for each language. When uninstalling, the application removes only the satellite assemblies associated with a given language and .NET Framework version. No core .NET Framework files are removed unless the last language for that .NET Framework version is being removed.
12. What is Global Assembly Cache (GAC) and what is the purpose of it?
Each computer where the common language runtime is installed has a machine-wide code cache called the global assembly cache. The global assembly cache stores assemblies specifically designated to be shared by several applications on the computer. You should share assemblies by installing them into the global assembly cache only when you need to.
13. What is Reflection in .NET?
All .NET compilers produce metadata about the types defined in the modules they produce. This metadata is packaged along with the module (modules in turn are packaged together in assemblies), and can be accessed by a mechanism called reflection. The System.Reflection namespace contains classes that can be used to interrogate the types for a module/assembly.
14. What is the managed and unmanaged code in .net?
The .NET Framework provides a run-time environment called the Common Language Runtime, which manages the execution of code and provides services that make the development process easier. Compilers and tools expose the runtime's functionality and enable you to write code that benefits from this managed execution environment. Code that you develop with a language compiler that targets the runtime is called managed code; it benefits from features such as cross-language integration, cross-language exception handling, enhanced security, versioning and deployment support, a simplified model for component interaction, and debugging and profiling services
15. What are Namespaces?
The namespace keyword is used to declare a scope. This namespace scope lets you organize code and gives you a way to create globally-unique types. Even if you do not explicitly declare one, a default namespace is created. This unnamed namespace, sometimes called the global namespace, is present in every file. Any identifier in the global namespace is available for use in a named namespace. Namespaces implicitly have public access and this is not modifiable.
16. What are the access-specifiers available in c#?
Private, Protected, Public, Internal, Protected Internal.
17. Advantage of ADO.Net?
ADO.NET Does Not Depend On Continuously Live Connections
Database Interactions Are Performed Using Data Commands
Data Can Be Cached in Datasets
Datasets Are Independent of Data Sources
Data Is Persisted as XML
Schemas Define Data Structures
18. Difference between OLEDB Provider and SqlClient ?
SQLClient .NET classes are highly optimized for the .net / sqlserver combination and achieve optimal results. The SqlClient data provider is fast. It's faster than the Oracle provider, and faster than accessing database via the OleDb layer. It's faster because it accesses the native library (which automatically gives you better performance), and it was written with lots of help from the SQL Server team.
19. Differences between dataset.clone and dataset.copy?
Clone - Copies the structure of the DataSet, including all DataTable schemas, relations, and constraints.Does not copy any data
Copy - Copies both the structure and data for this DataSet.
20. In a Webservice, need to display 10 rows from a table. So DataReader or DataSet is best choice?
WebService will support only DataSet.
21. What is Remoting?
The process of communication between different operating system processes, regardless of whether they are on the same computer. The .NET remoting system is an architecture designed to simplify communication between objects living in different application domains, whether on the same computer or not, and between different contexts, whether in the same application domain or not.
22. 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.
23. What’s a delegate?
A delegate object encapsulates a reference to a method. In C++ they were referred to as function pointers.
24. What’s an interface class?
It’s an abstract class with public abstract methods all of which must be implemented in the inherited classes
25. What is the transport protocol you use to call a Web service
SOAP is the preferred protocol.
Interview questions for C# developers
Useful for preparation, but too specific to be used in the interview.
1. Is it possible to inline assembly or IL in C# code? - No.
2. Is it possible to have different access modifiers on the get/set methods of a property? - No. The access modifier on a property applies to both its get and set accessors. What you need to do if you want them to be different is make the property read-only (by only providing a get accessor) and create a private/internal set method that is separate from the property.
3. Is it possible to have a static indexer in C#? - No. Static indexers are not allowed in C#.
4. If I return out of a try/finally in C#, does the code in the finally-clause run? - Yes. The code in the finally always runs. If you return out of the try block, or even if you do a “goto” out of the try, the finally block always runs:
using System;
class main
{
public static void Main()
{
try
{
Console.WriteLine("In Try block");
return;
}
finally
{
Console.WriteLine("In Finally block");
}
}
}
Both “In Try block” and “In Finally block” will be displayed. Whether the return is in the try block or after the try-finally block, performance is not affected either way. The compiler treats it as if the return were outside the try block anyway. If it’s a return without an expression (as it is above), the IL emitted is identical whether the return is inside or outside of the try. If the return has an expression, there’s an extra store/load of the value of the expression (since it has to be computed within the try block).
5. I was trying to use an “out int” parameter in one of my functions. How should I declare the variable that I am passing to it? - You should declare the variable as an int, but when you pass it in you must specify it as ‘out’, like the following: int i; foo(out i); where foo is declared as follows: [return-type] foo(out int o) { }
6. How does one compare strings in C#? - In the past, you had to call .ToString() on the strings when using the == or != operators to compare the strings’ values. That will still work, but the C# compiler now automatically compares the values instead of the references when the == or != operators are used on string types. If you actually do want to compare references, it can be done as follows: if ((object) str1 == (object) str2) { … } Here’s an example showing how string compares work:
7. using System;
8. public class StringTest
9. {
10. public static void Main(string[] args)
11. {
12. Object nullObj = null; Object realObj = new StringTest();
13. int i = 10;
14. Console.WriteLine("Null Object is [" + nullObj + "]n"
15. + "Real Object is [" + realObj + "]n"
16. + "i is [" + i + "]n");
17. // Show string equality operators
18. string str1 = "foo";
19. string str2 = "bar";
20. string str3 = "bar";
21. Console.WriteLine("{0} == {1} ? {2}", str1, str2, str1 == str2 );
22. Console.WriteLine("{0} == {1} ? {2}", str2, str3, str2 == str3 );
23. }
24. }
Output:
Null Object is []
Real Object is [StringTest]
i is [10]
foo == bar ? False
bar == bar ? True
25. How do you specify a custom attribute for the entire assembly (rather than for a class)? - Global attributes must appear after any top-level using clauses and before the first type or namespace declarations. An example of this is as follows:
26. using System;
27. [assembly : MyAttributeClass] class X {}
Note that in an IDE-created project, by convention, these attributes are placed in AssemblyInfo.cs.
28. How do you mark a method obsolete? -
[Obsolete] public int Foo() {...}
or
[Obsolete("This is a message describing why this method is obsolete")] public int Foo() {...}
Note: The O in Obsolete is always capitalized.
29. How do you implement thread synchronization (Object.Wait, Notify,and CriticalSection) in C#? - You want the lock statement, which is the same as Monitor Enter/Exit:
30. lock(obj) { // code }
translates to
try {
CriticalSection.Enter(obj);
// code
}
finally
{
CriticalSection.Exit(obj);
}
31. How do you directly call a native function exported from a DLL? - Here’s a quick example of the DllImport attribute in action:
32. using System.Runtime.InteropServices;
33. class C
34. {
35. [DllImport("user32.dll")]
36. public static extern int MessageBoxA(int h, string m, string c, int type);
37. public static int Main()
38. {
39. return MessageBoxA(0, "Hello World!", "Caption", 0);
40. }
41. }
This example shows the minimum requirements for declaring a C# method that is implemented in a native DLL. The method C.MessageBoxA() is declared with the static and external modifiers, and has the DllImport attribute, which tells the compiler that the implementation comes from the user32.dll, using the default name of MessageBoxA. For more information, look at the Platform Invoke tutorial in the documentation.
42. How do I simulate optional parameters to COM calls? - You must use the Missing class and pass Missing.Value (in System.Reflection) for any values that have optional parameters.
C# .NET interview questions
Good for preparation and general self-testing, but too specific for the actual job interview. This was sent in by a job applicant getting ready to step into the .NET field in India.
1. 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.
2. Why does DllImport not work for me? - All methods marked with the DllImport attribute must be marked as public static extern.
3. Why does my Windows application pop up a console window every time I run it? - Make sure that the target type set in the project properties setting is set to Windows Application, and not Console Application. If you’re using the command line, compile with /target:winexe, not /target:exe.
4. Why do I get an error (CS1006) when trying to declare a method without specifying a return type? - If you leave off the return type on a method declaration, the compiler thinks you are trying to declare a constructor. So if you are trying to declare a method that returns nothing, use void. The following is an example: // This results in a CS1006 error public static staticMethod (mainStatic obj) // This will work as wanted public static void staticMethod (mainStatic obj)
5. Why do I get a syntax error when trying to declare a variable called checked? - The word checked is a keyword in C#.
6. 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 System.Security.SecurityException. 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.
7. Why do I get a CS5001: does not have an entry point defined error when compiling? - The most common problem is that you used a lowercase ‘m’ when defining the Main method. The correct way to implement the entry point is as follows: class test { static void Main(string[] args) {} }
8. What optimizations does the C# compiler perform when you use the /optimize+ compiler option? - The following is a response from a developer on the C# compiler team: We get rid of unused locals (i.e., locals that are never read, even if assigned). We get rid of unreachable code. We get rid of try-catch with an empty try. We get rid of try-finally with an empty try. We get rid of try-finally with an empty finally. We optimize branches over branches: gotoif A, lab1 goto lab2: lab1: turns into: gotoif !A, lab2 lab1: We optimize branches to ret, branches to next instruction, and branches to branches.
9. What is the syntax for calling an overloaded constructor within a constructor (this() and constructorname() does not compile)? - The syntax for calling another constructor is as follows: class B { B(int i) { } } class C : B { C() : base(5) // call base constructor B(5) { } C(int i) : this() // call C() { } public static void Main() {} }
10. What is the equivalent to regsvr32 and regsvr32 /u a file in .NET development? - Try using RegAsm.exe. Search MSDN on Assembly Registration Tool.
11. What is the difference between a struct and a class in C#? - From language spec: The list of similarities between classes and structs is as follows. Longstructs can implement interfaces and can have the same kinds of members as classes. Structs differ from classes in several important ways; however, structs are value types rather than reference types, and inheritance is not supported for structs. Struct values are stored on the stack or in-line. Careful programmers can sometimes enhance performance through judicious use of structs. For example, the use of a struct rather than a class for a Point can make a large difference in the number of memory allocations performed at runtime. The program below creates and initializes an array of 100 points. With Point implemented as a class, 101 separate objects are instantiated-one for the array and one each for the 100 elements.
12. My switch statement works differently than in C++! Why? - C# does not support an explicit fall through for case blocks. The following code is not legal and will not compile in C#:
13. switch(x)
14. {
15. case 0: // do something
16. case 1: // do something as continuation of case 0
17. default: // do something in common with
18. //0, 1 and everything else
19. break;
20. }
To achieve the same effect in C#, the code must be modified as shown below (notice how the control flows are explicit):
class Test
{
public static void Main() {
int x = 3;
switch(x)
{
case 0: // do something
goto case 1;
case 1: // do something in common with 0
goto default;
default: // do something in common with 0, 1, and anything else
break;
}
}
}
21. Is there regular expression (regex) support available to C# developers? - Yes. The .NET class libraries provide support for regular expressions. Look at the System.Text.RegularExpressions namespace.
22. Is there any sample C# code for simple threading? - Yes:
23. using System;
24. using System.Threading;
25. class ThreadTest
26. {
27. public void runme()
28. {
29. Console.WriteLine("Runme Called");
30. }
31. public static void Main(String[] args)
32. {
33. ThreadTest b = new ThreadTest();
34. Thread t = new Thread(new ThreadStart(b.runme));
35. t.Start();
36. }
}
37. Is there an equivalent of exit() for quitting a C# .NET application? - Yes, you can use System.Environment.Exit(int exitCode) to exit the application or Application.Exit() if it’s a Windows Forms app.
38. Is there a way to force garbage collection? - Yes. Set all references to null and then call System.GC.Collect(). If you need to have some objects destructed, and System.GC.Collect() doesn’t seem to be doing it for you, you can force finalizers to be run by setting all the references to the object to null and then calling System.GC.RunFinalizers().
39. Is there a way of specifying which block or loop to break out of when working with nested loops? - The easiest way is to use goto:
40. using System;
41. class BreakExample
42. {
43. public static void Main(String[] args) {
44. for(int i=0; i<3; i++)
45. {
46. Console.WriteLine("Pass {0}: ", i);
47. for( int j=0 ; j<100 ; j++ )
48. {
49. if ( j == 10)
50. goto done;
51. Console.WriteLine("{0} ", j);
52. }
53. Console.WriteLine("This will not print");
54. }
55. done:
56. Console.WriteLine("Loops complete.");
57. }
58. }
59. Is it possible to restrict the scope of a field/method of a class to the classes in the same namespace? - There is no way to restrict to a namespace. Namespaces are never units of protection. But if you’re using assemblies, you can use the ‘internal’ access modifier to restrict access to only within the assembly.
# developer interview questions
A representative of a high-tech company in United Kingdom sent this in today noting that the list was used for interviewing a C# .NET developer. Any corrections and suggestions would be forwarded to the author. I won’t disclose the name of the company, since as far as I know they might still be using this test for prospective employees. Correct answers are in green color.
1) The C# keyword ‘int’ maps to which .NET type?
1. System.Int16
2. System.Int32
3. System.Int64
4. System.Int128
2) Which of these string definitions will prevent escaping on backslashes in C#?
1. string s = #”n Test string”;
2. string s = “’n Test string”;
3. string s = @”n Test string”;
4. string s = “n Test string”;
3) Which of these statements correctly declares a two-dimensional array in C#?
1. int[,] myArray;
2. int[][] myArray;
3. int[2] myArray;
4. System.Array[2] myArray;
4) If a method is marked as protected internal who can access it?
1. Classes that are both in the same assembly and derived from the declaring class.
2. Only methods that are in the same class as the method in question.
3. Internal methods can be only be called using reflection.
4. Classes within the same assembly, and classes derived from the declaring class.
5) What is boxing?
a) Encapsulating an object in a value type.
b) Encapsulating a copy of an object in a value type.
c) Encapsulating a value type in an object.
d) Encapsulating a copy of a value type in an object.
6) What compiler switch creates an xml file from the xml comments in the files in an assembly?
1. /text
2. /doc
3. /xml
4. /help
7) What is a satellite Assembly?
1. A peripheral assembly designed to monitor permissions requests from an application.
2. Any DLL file used by an EXE file.
3. An assembly containing localized resources for another assembly.
4. An assembly designed to alter the appearance or ‘skin’ of an application.
8) What is a delegate?
1. A strongly typed function pointer.
2. A light weight thread or process that can call a single method.
3. A reference to an object in a different process.
4. An inter-process message channel.
9) How does assembly versioning in .NET prevent DLL Hell?
1. The runtime checks to see that only one version of an assembly is on the machine at any one time.
2. .NET allows assemblies to specify the name AND the version of any assemblies they need to run.
3. The compiler offers compile time checking for backward compatibility.
4. It doesn’t.
10) Which “Gang of Four” design pattern is shown below?
public class A {
private A instance;
private A() {
}
public
static A Instance {
get
{
if ( A == null )
A = new A();
return instance;
}
}
}
1. Factory
2. Abstract Factory
3. Singleton
4. Builder
11) In the NUnit test framework, which attribute must adorn a test class in order for it to be picked up by the NUnit GUI?
1. TestAttribute
2. TestClassAttribute
3. TestFixtureAttribute
4. NUnitTestClassAttribute
12) Which of the following operations can you NOT perform on an ADO.NET DataSet?
1. A DataSet can be synchronised with the database.
2. A DataSet can be synchronised with a RecordSet.
3. A DataSet can be converted to XML.
4. You can infer the schema from a DataSet.
13) In Object Oriented Programming, how would you describe encapsulation?
1. The conversion of one type of object to another.
2. The runtime resolution of method calls.
3. The exposition of data.
4. The separation of interface and implementation.
ASP.NET DataGrid questions
1. What is datagrid? The DataGrid Web server control is a powerful tool for displaying information from a data source. It is easy to use; you can display editable data in a professional-looking grid by setting only a few properties. At the same time, the grid has a sophisticated object model that provides you with great flexibility in how you display the data.
2. What’s the difference between the System.Web.UI.WebControls.DataGrid and and System.Windows.Forms.DataGrid? The Web UI control does not inherently support master-detail data structures. As with other Web server controls, it does not support two-way data binding. If you want to update data, you must write code to do this yourself. You can only edit one row at a time. It does not inherently support sorting, although it raises events you can handle in order to sort the grid contents. You can bind the Web Forms DataGrid to any object that supports the IEnumerable interface. The Web Forms DataGrid control supports paging. It is easy to customize the appearance and layout of the Web Forms DataGrid control as compared to the Windows Forms one.
3. How do you customize the column content inside the datagrid? If you want to customize the content of a column, make the column a template column. Template columns work like item templates in the DataList or Repeater control, except that you are defining the layout of a column rather than a row.
4. How do you apply specific formatting to the data inside the cells? You cannot specify formatting for columns generated when the grid’s AutoGenerateColumns property is set to true, only for bound or template columns. To format, set the column’s DataFormatString property to a string-formatting expression suitable for the data type of the data you are formatting.
5. How do you hide the columns? One way to have columns appear dynamically is to create them at design time, and then to hide or show them as needed. You can do this by setting a column’s Visible property.
6. How do you display an editable drop-down list? Displaying a drop-down list requires a template column in the grid. Typically, the ItemTemplate contains a control such as a data-bound Label control to show the current value of a field in the record. You then add a drop-down list to the EditItemTemplate. In Visual Studio, you can add a template column in the Property builder for the grid, and then use standard template editing to remove the default TextBox control from the EditItemTemplate and drag a DropDownList control into it instead. Alternatively, you can add the template column in HTML view. After you have created the template column with the drop-down list in it, there are two tasks. The first is to populate the list. The second is to preselect the appropriate item in the list — for example, if a book’s genre is set to “fiction,” when the drop-down list displays, you often want “fiction” to be preselected.
7. How do you check whether the row data has been changed? The definitive way to determine whether a row has been dirtied is to handle the changed event for the controls in a row. For example, if your grid row contains a TextBox control, you can respond to the control’s TextChanged event. Similarly, for check boxes, you can respond to a CheckedChanged event. In the handler for these events, you maintain a list of the rows to be updated. Generally, the best strategy is to track the primary keys of the affected rows. For example, you can maintain an ArrayList object that contains the primary keys of the rows to update.
Windows code security questions
1. What’s the difference between code-based security and role-based security? Which one is better? Code security is the approach of using permissions and permission sets for a given code to run. The admin, for example, can disable running executables off the Internet or restrict access to corporate database to only few applications. Role-based security most of the time involves the code running with the privileges of the current user. This way the code cannot supposedly do more harm than mess up a single user account. There’s no better, or 100% thumbs-up approach, depending on the nature of deployment, both code-based and role-based security could be implemented to an extent.
2. How can you work with permissions from your .NET application? You can request permission to do something and you can demand certain permissions from other apps. You can also refuse permissions so that your app is not inadvertently used to destroy some data.
3. How can C# app request minimum permissions?
using System.Security.Permissions;
[assembly:FileDialogPermissionAttribute(SecurityAction.RequestMinimum, Unrestricted=true)]
4. What’s a code group? A code group is a set of assemblies that share a security context.
5. What’s the difference between authentication and authorization? Authentication happens first. You verify user’s identity based on credentials. Authorization is making sure the user only gets access to the resources he has credentials for.
6. What are the authentication modes in ASP.NET? None, Windows, Forms and Passport.
7. Are the actual permissions for the application defined at run-time or compile-time? The CLR computes actual permissions at runtime based on code group membership and the calling chain of the code.
NET Deployment questions
1. What do you know about .NET assemblies? Assemblies are the smallest units of versioning and deployment in the .NET application. Assemblies are also the building blocks for programs such as Web services, Windows services, serviced components, and .NET remoting applications.
2. What’s the difference between private and shared assembly? Private assembly is used inside an application only and does not have to be identified by a strong name. Shared assembly can be used by multiple applications and has to have a strong name.
3. What’s a strong name? A strong name includes the name of the assembly, version number, culture identity, and a public key token.
4. How can you tell the application to look for assemblies at the locations other than its own install? Use the
directive in the XML .config file for a given application.
should do the trick. Or you can add additional search paths in the Properties box of the deployed application.
5. How can you debug failed assembly binds? Use the Assembly Binding Log Viewer (fuslogvw.exe) to find out the paths searched.
6. Where are shared assemblies stored? Global assembly cache.
7. How can you create a strong name for a .NET assembly? With the help of Strong Name tool (sn.exe).
8. Where’s global assembly cache located on the system? Usually C:\winnt\assembly or C:\windows\assembly.
9. Can you have two files with the same file name in GAC? Yes, remember that GAC is a very special folder, and while normally you would not be able to place two files with the same name into a Windows folder, GAC differentiates by version number as well, so it’s possible for MyApp.dll and MyApp.dll to co-exist in GAC if the first one is version 1.0.0.0 and the second one is 1.1.0.0.
10. So let’s say I have an application that uses MyApp.dll assembly, version 1.0.0.0. There is a security bug in that assembly, and I publish the patch, issuing it under name MyApp.dll 1.1.0.0. How do I tell the client applications that are already installed to start using this new MyApp.dll? Use publisher policy. To configure a publisher policy, use the publisher policy configuration file, which uses a format similar app .config file. But unlike the app .config file, a publisher policy file needs to be compiled into an assembly and placed in the GAC.
11. What is delay signing? Delay signing allows you to place a shared assembly in the GAC by signing the assembly with just the public key. This allows the assembly to be signed with the private key at a later stage, when the development process is complete and the component or assembly is ready to be deployed. This process enables developers to work with shared assemblies as if they were strongly named, and it secures the private key of the signature from being accessed at different stages of development.
ASP.NET questions, part 1
1. Explain the differences between Server-side and Client-side code? Server side scripting means that all the script will be executed by the server and interpreted as needed. ASP doesn’t have some of the functionality like sockets, uploading, etc. For these you have to make a custom components usually in VB or VC++. Client side scripting means that the script will be executed immediately in the browser such as form field validation, clock, email validation, etc. Client side scripting is usually done in VBScript or JavaScript. Download time, browser compatibility, and visible code - since JavaScript and VBScript code is included in the HTML page, then anyone can see the code by viewing the page source. Also a possible security hazards for the client computer.
2. What type of code (server or client) is found in a Code-Behind class? C#
3. Should validation (did the user enter a real date) occur server-side or client-side? Why? Client-side validation because there is no need to request a server side date when you could obtain a date from the client machine.
4. What does the "EnableViewState" property do? Why would I want it on or off? Enable ViewState turns on the automatic state management feature that enables server controls to re-populate their values on a round trip without requiring you to write any code. This feature is not free however, since the state of a control is passed to and from the server in a hidden form field. You should be aware of when ViewState is helping you and when it is not. For example, if you are binding a control to data on every round trip (as in the datagrid example in tip #4), then you do not need the control to maintain it’s view state, since you will wipe out any re-populated data in any case. ViewState is enabled for all server controls by default. To disable it, set the EnableViewState property of the control to false.
5. What is the difference between Server.Transfer and Response.Redirect? Why would I choose one over the other? Server.Transfer() : client is shown as it is on the requesting page only, but the all the content is of the requested page. Data can be persist accros the pages using Context.Item collection, which is one of the best way to transfer data from one page to another keeping the page state alive. Response.Dedirect() :client know the physical loation (page name and query string as well). Context.Items loses the persisitance when nevigate to destination page. In earlier versions of IIS, if we wanted to send a user to a new Web page, the only option we had was Response.Redirect. While this method does accomplish our goal, it has several important drawbacks. The biggest problem is that this method causes each page to be treated as a separate transaction. Besides making it difficult to maintain your transactional integrity, Response.Redirect introduces some additional headaches. First, it prevents good encapsulation of code. Second, you lose access to all of the properties in the Request object. Sure, there are workarounds, but they’re difficult. Finally, Response.Redirect necessitates a round trip to the client, which, on high-volume sites, causes scalability problems. As you might suspect, Server.Transfer fixes all of these problems. It does this by performing the transfer on the server without requiring a roundtrip to the client.
6. Can you give an example of when it would be appropriate to use a web service as opposed to a non-serviced .NET component? When to Use Web Services:
o Communicating through a Firewall When building a distributed application with 100s/1000s of users spread over multiple locations, there is always the problem of communicating between client and server because of firewalls and proxy servers. Exposing your middle tier components as Web Services and invoking the directly from a Windows UI is a very valid option.
o Application Integration When integrating applications written in various languages and running on disparate systems. Or even applications running on the same platform that have been written by separate vendors.
o Business-to-Business Integration This is an enabler for B2B intergtation which allows one to expose vital business processes to authorized supplier and customers. An example would be exposing electronic ordering and invoicing, allowing customers to send you purchase orders and suppliers to send you invoices electronically.
o Software Reuse This takes place at multiple levels. Code Reuse at the Source code level or binary componet-based resuse. The limiting factor here is that you can reuse the code but not the data behind it. Webservice overcome this limitation. A scenario could be when you are building an app that aggregates the functionality of serveral other Applicatons. Each of these functions could be performed by individual apps, but there is value in perhaps combining the the multiple apps to present a unifiend view in a Portal or Intranet.
o When not to use Web Services: Single machine Applicatons When the apps are running on the same machine and need to communicate with each other use a native API. You also have the options of using component technologies such as COM or .NET Componets as there is very little overhead.
o Homogeneous Applications on a LAN If you have Win32 or Winforms apps that want to communicate to their server counterpart. It is much more efficient to use DCOM in the case of Win32 apps and .NET Remoting in the case of .NET Apps.
7. Let’s say I have an existing application written using Visual Studio (VBInterDevand this application utilizes WindowsCOM+ transaction services. How would you approach migrating this application to .NET?
8. Can you explain the difference between an ADO.NET Dataset and an ADO Recordset? In ADO, the in-memory representation of data is the recordset. In ADO.NET, it is the dataset. There are important differences between them.
o A recordset looks like a single table. If a recordset is to contain data from multiple database tables, it must use a JOIN query, which assembles the data from the various database tables into a single result table. In contrast, a dataset is a collection of one or more tables. The tables within a dataset are called data tables; specifically, they are DataTable objects. If a dataset contains data from multiple database tables, it will typically contain multiple DataTable objects. That is, each DataTable object typically corresponds to a single database table or view. In this way, a dataset can mimic the structure of the underlying database. A dataset usually also contains relationships. A relationship within a dataset is analogous to a foreign-key relationship in a database —that is, it associates rows of the tables with each other. For example, if a dataset contains a table about investors and another table about each investor’s stock purchases, it could also contain a relationship connecting each row of the investor table with the corresponding rows of the purchase table. Because the dataset can hold multiple, separate tables and maintain information about relationships between them, it can hold much richer data structures than a recordset, including self-relating tables and tables with many-to-many relationships.
o In ADO you scan sequentially through the rows of the recordset using the ADO MoveNext method. In ADO.NET, rows are represented as collections, so you can loop through a table as you would through any collection, or access particular rows via ordinal or primary key index. DataRelation objects maintain information about master and detail records and provide a method that allows you to get records related to the one you are working with. For example, starting from the row of the Investor table for "Nate Sun," you can navigate to the set of rows of the Purchase table describing his purchases. A cursor is a database element that controls record navigation, the ability to update data, and the visibility of changes made to the database by other users. ADO.NET does not have an inherent cursor object, but instead includes data classes that provide the functionality of a traditional cursor. For example, the functionality of a forward-only, read-only cursor is available in the ADO.NET DataReader object. For more information about cursor functionality, see Data Access Technologies.
o Minimized Open Connections: In ADO.NET you open connections only long enough to perform a database operation, such as a Select or Update. You can read rows into a dataset and then work with them without staying connected to the data source. In ADO the recordset can provide disconnected access, but ADO is designed primarily for connected access. There is one significant difference between disconnected processing in ADO and ADO.NET. In ADO you communicate with the database by making calls to an OLE DB provider. In ADO.NET you communicate with the database through a data adapter (an OleDbDataAdapter, SqlDataAdapter, OdbcDataAdapter, or OracleDataAdapter object), which makes calls to an OLE DB provider or the APIs provided by the underlying data source. The important difference is that in ADO.NET the data adapter allows you to control how the changes to the dataset are transmitted to the database — by optimizing for performance, performing data validation checks, or adding any other extra processing. Data adapters, data connections, data commands, and data readers are the components that make up a .NET Framework data provider. Microsoft and third-party providers can make available other .NET Framework data providers that can be integrated into Visual Studio.
o Sharing Data Between Applications. Transmitting an ADO.NET dataset between applications is much easier than transmitting an ADO disconnected recordset. To transmit an ADO disconnected recordset from one component to another, you use COM marshalling. To transmit data in ADO.NET, you use a dataset, which can transmit an XML stream.
o Richer data types.COM marshalling provides a limited set of data types — those defined by the COM standard. Because the transmission of datasets in ADO.NET is based on an XML format, there is no restriction on data types. Thus, the components sharing the dataset can use whatever rich set of data types they would ordinarily use.
o Performance. Transmitting a large ADO recordset or a large ADO.NET dataset can consume network resources; as the amount of data grows, the stress placed on the network also rises. Both ADO and ADO.NET let you minimize which data is transmitted. But ADO.NET offers another performance advantage, in that ADO.NET does not require data-type conversions. ADO, which requires COM marshalling to transmit records sets among components, does require that ADO data types be converted to COM data types.
o Penetrating Firewalls.A firewall can interfere with two components trying to transmit disconnected ADO recordsets. Remember, firewalls are typically configured to allow HTML text to pass, but to prevent system-level requests (such as COM marshalling) from passing.
9. Can you give an example of what might be best suited to place in the Application_Start and Session_Start subroutines? The Application_Start event is guaranteed to occur only once throughout the lifetime of the application. It’s a good place to initialize global variables. For example, you might want to retrieve a list of products from a database table and place the list in application state or the Cache object. SessionStateModule exposes both Session_Start and Session_End events.
10. If I’m developing an application that must accomodate multiple security levels though secure login and my ASP.NET web appplication is spanned across three web-servers (using round-robbin load balancing) what would be the best approach to maintain login-in state for the users?
11. What are ASP.NET Web Forms? How is this technology different than what is available though ASP? Web Forms are the heart and soul of ASP.NET. Web Forms are the User Interface (UI) elements that give your Web applications their look and feel. Web Forms are similar to Windows Forms in that they provide properties, methods, and events for the controls that are placed onto them. However, these UI elements render themselves in the appropriate markup language required by the request, e.g. HTML. If you use Microsoft Visual Studio .NET, you will also get the familiar drag-and-drop interface used to create your UI for your Web application.
12. How does VB.NET/C# achieve polymorphism? By using Abstract classes/functions.
13. Can you explain what inheritance is and an example of when you might use it? Inheritance is a fundamental feature of an object oriented system and it is simply the ability to inherit data and functionality from a parent object. Rather than developing new objects from scratch, new code can be based on the work of other programmers, adding only new features that are needed.
14. How would you implement inheritance using VB.NET/C#? When we set out to implement a class using inheritance, we must first start with an existing class from which we will derive our new subclass. This existing class, or base class, may be part of the .NET system class library framework, it may be part of some other application or .NET assembly, or we may create it as part of our existing application. Once we have a base class, we can then implement one or more subclasses based on that base class. Each of our subclasses will automatically have all of the methods, properties, and events of that base class ? including the implementation behind each method, property, and event. Our subclass can add new methods, properties, and events of its own - extending the original interface with new functionality. Additionally, a subclass can replace the methods and properties of the base class with its own new implementation - effectively overriding the original behavior and replacing it with new behaviors. Essentially inheritance is a way of merging functionality from an existing class into our new subclass. Inheritance also defines rules for how these methods, properties, and events can be merged.
ASP.NET questions, part 2
1. Whats an assembly? Assemblies are the building blocks of .NET Framework applications; they form the fundamental unit of deployment, version control, reuse, activation scoping, and security permissions. An assembly is a collection of types and resources that are built to work together and form a logical unit of functionality. An assembly provides the common language runtime with the information it needs to be aware of type implementations. To the runtime, a type does not exist outside the context of an assembly.
2. Describe the difference between inline and code behind - which is best in a loosely coupled solution? ASP.NET supports two modes of page development: Page logic code that is written inside