C# Interview Questions and Answers Part 10

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


What’s the .NET collection class that allows an element to be accessed using a unique key?
HashTable.


What class is underneath the SortedList class?
A sorted HashTable.


Will the finally block get executed if an exception has not occurred?Yes.


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 {}.


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).


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).


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


Can you prevent your class from being inherited by another class?
Yes. The keyword “sealed” will prevent the class from being inherited.


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.


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.


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.


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.


Why can’t you specify the accessibility modifier for methods inside the interface?
They all must be public, and are therefore public by default.


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


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.