.Net core interview Q & A

Top 20 Q & A

 https://www.dotnettricks.com/learn/aspnetcore/top-20-asp-net-core-interview-questions-and-answers

Top 60

https://www.qfles.com/interview-question/asp-net-core-interview-questions

Can an abstract class have a constructor ?

Yes, an abstract class can have a constructor. 

In general, a class constructor is used to initialize fields. Along the same lines, an abstract class constructor is used to initialize fields of the abstract class.

An abstract class constructor can also be used to execute code that is relevant for every child class. This prevents duplicate code.

You can not create an instance of an abstract class, so what is the use of a constructor in an abstract class?

You can not create an instance of the abstract class, we can create instances of the classes that are derived from the abstract class.

So, when an instance of the derived class is created, the parent abstract class constructor is automatically called.

Note: Abstract class cant be directly instantiated, The abstract class constructors get executed thru a derived class. So, it is a good practice to use a protected modifier with an abstract class constructor,using public doesn't make sense.

.NET Framework vs .Net Core 3.1

 

Sr. No.	Comparison	.Net Framework	.Net Core 3.1
1	Cross Platforms	.Net framework runs only on windows	.Net core is cross-platform, it operates on Windows, Linux, and Mac operating systems
2	Performance	Slow	Better
3	Application supported	the .NET framework is for developing desktop applications, web applications, and web services, WPF, ASP.NET MVC	MVC core 3.x
4	WCF/ WPF/WWF	Yes	No
5	Desktop Based	WPF, Winforms.	Nothing for desktop
6	Packaging	Packaged as big framework	Delivered via modularity using Nuget
7	Microservice Support	No	Yes
8	CLI Tools	More IDE Based	Full CLI command supported
9	Mobile Compatibility	No direct support	with .Net standard compatible with Xamarin
9	Cloud	Runs only on windows	Yes

What is the differnece between Abstract class & Interface?

In an abstract class, we can create the functionality and that needs to be implemented by the derived class. The interface allows us to define the functionality or functions but cannot implement that. The derived class extends the interface and implements those functions.

Abstract Class	Interface
Abstract classes are inherited.	Interfaces are Implemented.
It is a half-defined parent class.	It is a contract.
Share some common logic in child classes	Planning Abstraction.
It contains both declaration and definition parts.	It contains only a declaration part.
It contains both declaration and definition parts.	It contains only a declaration part.
Multiple inheritance is not achieved by abstract class.	Multiple inheritance is achieved by interface.
It contain constructor.	It does not contain constructor.
It can contain static members.	It does not contain static members.
It can contain different types of access modifiers like public, private, protected etc.	It only contains public access modifier because everything in the interface is public.
The performance of an abstract class is fast.	The performance of interface is slow because it requires time to search actual method in the corresponding class.
It is used to implement the core identity of class.	It is used to implement peripheral abilities of class.
A class can only use one abstract class.	A class can use multiple interface.
If many implementations are of the same kind and use common behavior, then it is superior to use abstract class.	If many implementations only share methods, then it is superior to use Interface.
Abstract class can contain methods, fields, constants, etc.	Interface can only contain methods .
It can be fully, partially or not implemented.	It should be fully implemented.

Sr. No.	Key	Abstract Class	Interface
1	Definition	In terms of standard definition, an Abstract class is, conceptually, a class that cannot be instantiated and is usually implemented as a class that has one or more pure virtual (abstract) functions.	On other hand an Interface is a description of what member functions must a class, which inherits this interface, implement. In other words, an interface describes behaviour of the class.
2	Implementation	As like of other general class design in C# Abstract class also have its own implementation along with its declaration.	On other hand an Interface can only have a signature, not the implementation. While its implementation is being provided by the class which implements it.
3	Inheritance	As per specification in C# a class can extends only one other class hence multiple inheritance is not achieved by abstract class.	On other hand in case of Interface a class can implements multiple interfaces and hence multiple inheritance is achieved by interface.
4	Constructor	Like other classes in C# for instantiation abstract class also have constructor which provide an instance of abstract class to access its non-static methods.	On other hand Interface do not have constructor so we can't instantiate an interface directly although its method could get accessed by creating instance of class which implementing it.
5	Modifiers	As abstract class is most like of other ordinary class in C# so it can contain different types of access modifiers like public, private, protected etc.	On other hand as Interface needs to be get implemented in order to provide its methods implementation by other class so can only contains public access modifier.
6	Performance	As abstract class have its method as well as their implementations also for its abstract methods implementation it have reference for its implementing class so performance is comparatively faster as compare to that of Interface.	On other hand the performance of interface is slow because it requires time to search actual method in the corresponding class.

Watch video to clear the concept-

https://www.youtube.com/watch?v=0EnSPBVrbG0

What is AJAX?

 Asynchronous JavaScript and XML (AJAX) is a development technique used to create interactive web applications or rich internet applications. AJAX uses a number of existing technologies together, including: XHTML, CSS, JavaScript, Document Object Model, XML, XSLT, and the XMLHttpRequest object.

With AJAX, web applications can retrieve data from the server asynchronously, in the background, without reloading the entire browser page. The use of AJAX has led to an increase in interactive animation on web pages.

Advantages

• Reduces the traffic travels between the client and the server. 
• No cross browser pain.
• Better interactivity and responsiveness.
• With AJAX, several multi purpose applications and features can be handled using a single web page(SPA).
• API's are good because those work with HTTP method and JavaScrtipt.

Disadvantages

• Search engines like Google would not be able to index an AJAX application. 
• It is totally built-in JavaScript code. If any user disables JS in the browser, it won't work.
• The server information can not be accessed within AJAX.
• Security is less in AJAX applications as all the files are downloaded at client side.
• The data of all requests is URL-encoded, which increases the size of the request.

For more details- 

https://www.c-sharpcorner.com/article/ajax-in-asp-net/ 

https://www.tutorialspoint.com/asp.net/asp.net_ajax_control.htm

https://www.aspsnippets.com/Articles/Call-ASPNet-Page-Method-using-jQuery-AJAX-Example.aspx