C# Interview Questions And Answers: part-1

Ques 1. What’s the implicit name of the parameter that gets passed into the class’ set method?
Ans : Value, and its datatype depends on whatever variable we’re changing.

Ques 2. How do you inherit from a class in C#?
Ans : Place a colon and then the name of the base class. Notice that it’s double colon in C++.

Ques 3. Does C# support multiple inheritance?
Ans : No, use interfaces instead.

Ques 4. When you inherit a protected class-level variable, who is it available to?
Ans : Classes in the same namespace.

Ques 5. Are private class-level variables inherited?
Ans : Yes, but they are not accessible, so looking at it you can honestly say that they are not inherited. But they are.

Ques 6. Describe the accessibility modifier protected internal?
Ans : It’s available to derived classes and classes within the same Assembly (and naturally from the base class it’s declared in).

Ques 7. 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?
Ans : 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.

Ques 8. What’s the top .NET class that everything is derived from?
Ans : System.Object.

Ques 9. How’s method overriding different from overloading?
Ans : When overriding, you change the method behavior for a derived class. Overloading simply involves having a method with the same name within the class.

Ques 10. What does the keyword virtual mean in the method definition?
Ans : The method can be over-ridden.

Ques 11. Can you declare the override method static while the original method is non-static?
Ans : No, you can’t, the signature of the virtual method must remain the same, only the keyword virtual is changed to keyword override.

Ques 12. Can you override private virtual methods?
Ans : No, moreover, you cannot access private methods in inherited classes, have to be protected in the base class to allow any sort of access.

Ques 13. Can you prevent your class from being inherited and becoming a base class for some other classes?
Ans : 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.

Ques 14. Can you allow class to be inherited, but prevent the method from being over-ridden?
Ans : Yes, just leave the class public and make the method sealed.

Ques 15. What’s an abstract class?
Ans : 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.

Ques 16. When do you absolutely have to declare a class as abstract (as opposed to free-willed educated choice or decision based on UML diagram)?
Ans : 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.

Ques 17. What’s an interface class?
Ans : It’s an abstract class with public abstract methods all of which must be implemented in the inherited classes.

Ques 18. Why can’t you specify the accessibility modifier for methods inside the interface?
Ans : 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.

Ques 19. And if they have conflicting method names?
Ans : 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.

Ques 20. What’s the difference between an interface and abstract class?
Ans : 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.

Ques 21. How can you overload a method?
Ans : Different parameter data types, different number of parameters, different order of parameters.

Ques 22. 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?
Ans : 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.

Ques 23. What’s the difference between System.String and System.StringBuilder classes?
Ans : System.String is immutable; System.StringBuilder was designed with the purpose of having a mutable string where a variety of operations can be performed.

Ques 24. What’s the advantage of using System.Text.StringBuilder over System.String?
Ans : 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.

Ques 25. What’s the difference between the System.Array.CopyTo() and System.Array.Clone()?
Ans : The first one performs a deep copy of the array, the second one is shallow.

Ques 26. How can you sort the elements of the array in descending order?
Ans : By calling Sort() and then Reverse() methods.

Ques 27. What’s the .NET datatype that allows the retrieval of data by a unique key?
Ans : HashTable.

Ques 28. What’s class SortedList underneath?
Ans : A sorted HashTable.

Ques 29. What’s the C# equivalent of C++ catch (…), which was a catch-all statement for any possible exception?
Ans : 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 {}.

Ques 30. Can multiple catch blocks be executed?
Ans : 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.