31. 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.
32. What does the keyword “virtual” declare for a method or property?
The method or property can be overridden.
33. 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.
34. Can you declare an override method to be static if the original method is non-static?
No. The signature of the virtual method must remain the same, only the keyword virtual is changed to keyword override.
35. Can you override private virtual methods?
No. Private methods are not accessible outside the class.
1. Original answer: No, moreover, you cannot access private methods in inherited classes, have to be protected in the base class to allow any sort of access.
36. What are the different ways a method can be overloaded?
Different parameter data types, different number of parameters, different order of parameters.
37. If a base class has a number of overloaded constructors, and an inherited 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.
38. 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.
39. What’s a delegate?
A delegate object encapsulates a reference to a method. In C++ they were referred to as function pointers.
40. What’s a multicast delegate?
It’s a delegate that points to and eventually fires off several methods.
41. 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.
42. What are the ways to deploy an assembly?
An MSI installer, a CAB archive, and XCOPY command.
C# IQ-55
C# IQ-54
19. What is 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.
1. To do: Improve the answer.
Class Questions
20. How do you inherit from a class in C#?
Place a colon and then the name of the base class.
21. Can you prevent your class from being inherited by another class?
Yes. The keyword “sealed” will prevent the class from being inherited.
22. 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.
23. 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.
24. When do you absolutely have to declare a class as abstract?
1. When at least one of the methods in the class is abstract.
2. When the class itself is inherited from an abstract class, but not all base abstract methods have been overridden.
25. What’s an interface class?
It’s an abstract class with public abstract methods all of which must be implemented in the inherited classes.
26. 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.
27. Can you inherit multiple interfaces?
Yes, why not.
28. 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.
29. What’s the difference between an interface and abstract class?
In an interface class, all methods must be abstract. In an abstract class some methods can be concrete. In an interface class, no accessibility modifiers are allowed, which is ok in an abstract class.
30. 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. (questions courtesy of Eyal)
Method and Property Questions
C# IQ-53
C# Interview Questions
What is Boxing & UnBoxing?
Converting a value type to reference type is called Boxing
Unboxing is an explicit operation.
What is hiding in CSharp ?
Hiding is also called as Shadowing. This is the concept of Overriding the methods. It is a concept used in the Object Oriented Programming.
What are jagged arrays in C# ?
Multiple dimension arrays in which rows are of different length
C# FAQs
1. Does C# support multiple-inheritance?
No, use interfaces instead.
2. When you inherit a protected class-level variable, who is it available to?
Classes in the same namespace.
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 derived classes and classes within the same Assembly (and naturally from the base class it’s declared in).
1. To do: Confirm the “within the same assembly” portion.
5. C# provides a default class constructor for me. I decide to write a constructor that takes a string as a parameter, but want to keep the constructor that has no parameter. 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.
6. What’s the top .NET class that everything is derived from?
System.Object.
8. 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.
9. What’s the advantage of using System.Text.StringBuilder over System.String?
StringBuilder is more efficient in cases where there is a large amount of string
manipulation. Strings are immutable, so each time it’s being operated on, a new instance is created.
10. Can you store multiple data types in System.Array? No.
11. What’s the difference between the System.Array.CopyTo() and System.Array.Clone()?
The first one performs a deep copy of the array, the second one is shallow.
12. How can you sort the elements of the array in descending order?
By calling Sort() and then Reverse() methods.
13. What’s the .NET class that allows the retrieval of a data element using a unique key?
HashTable.
14. What class is underneath the SortedList class?
A sorted HashTable.
15. Will the finally block get executed if an exception has not occurred?¬
Yes.
16. What’s the C# 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 {}.
1. To do: Bad question. Re-word.
17. 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.
18. Explain the three services model commonly know as a three-tier application.
Presentation (UI), business (logic and underlying code) and data (from storage or other sources).
