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Common .Net Interview Questions and Why are they asked?

There are many .Net Questions that every interviewer(in general) asks.
Through this, I am starting a series of discussions where in I'll be discussing these questions and provide ample satisfactory answers to them.

The intent here is to realise the importance of these questions and help the needy(those who are preparing for interviews) and also who believe in knowing the basics rather than just blindly implementing the .Net classes/Interfaces.

Starting the First part of this series is All time Classic question #1

Question: What is the difference between Abstract Classes and Interface?

The moment this question is asked the candidates generally start uttering the bookish definitions, some of them are .
a) Access modifiers: Interfaces--Implicitly Public() , Classes can use use Access Modifiers.
b) No implementation in Interfaces, Classes can have implementations as well.
c)Abstract classes can't be instantiated .

Some more experienced candidates might get into some further details, However the basic things to understand here is  if these two are that much close in implementing functionality why do we have these two separately in C#

I'm not trying to be an Expert here, all I am trying, is to get rid of this anxious question once for all by exploring it from some possible angles.

OOPS principle that is being tested by this question: Polymorphism

Without going into Polymorphism details, both of these(Interfaces and Abstract Classes) are a ways of achieving Polymorphism in the Code.

Let's consider an example

public void Gadgets(MyGadget gadget){

}

This method could accept any object that implemented MyGadget as the gadget argument, even though the implementations of MyGadget might be quite different.

 A Class may inherit from only one base class(in C# ), so if you want to use abstract classes to provide polymorphism to a group of classes, they must all inherit from that class.
Abstract classes may also provide members that have already been implemented. Therefore, you can ensure a certain amount of identical functionality with an abstract class, but cannot with an interface.

 Decide whether to use an interface or an abstract class to provide polymorphism for your components.

  • If creating multiple versions of your component is anticipated, create an abstract class. Abstract classes provide a simple and easy way to version components. By updating the base class, all inheriting classes are automatically updated with the change. Interfaces, on the other hand, cannot be changed once created. If a new version of an interface is required,  a whole new interface must be created.

  • If the functionality youbeing created will be useful across a wide range of disparate objects, use an interface. Abstract classes should be used primarily for objects that are closely related, whereas interfaces are best suited for providing common functionality to unrelated classes.

  • If designing small, concise bits of functionality, use interfaces. If  designing large functional units, use an abstract class.

  • If  common, implemented functionality among all implementations of the component is intended, use an abstract class. Abstract classes allow to partially implement class, whereas interfaces contain no implementation for any members.


Hope this helps in making the decision as to when to use interfaces and when to use Abstract Classes,

Soon, I'll try to cover other commonly asked interview question.

Till next we connect, Happy Coding.

 
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