keywords in c#

Question

what is the difference between abstract class and virtual class?

Krishna Rajput Singh · Answer

Hello, An abstract method is a method that must be implemented to make a concrete class. The declaration is in the abstract class (and any class with an abstract method must be an abstract class) and it must be implemented in a concrete class. A virtual function is a function that can be overridden in a derived class using the override, replacing the behavior in the superclass. If you don't override, you get the original behavior. If you do, you always get the new behavior. This opposed to not virtual function, that can not be overridden but can hide the original function. This is done using the new modifier.

Upendra Pratap Shahi · Answer

Abstract vs. Virtual in C# There are several keywords that can be used for inheritance in object-oriented programming languages. In C#, you can specify a method as abstract or virtual . In the concrete class, you must override any method marked as abstract . You can override virtual methods. In addition, you can provide new implementation for normal methods that are neither abstract nor virtual . In this case, it's recommended to use the new keyword. What's the difference between abstract and virtual methods? How can I use them to serve my design? In this article, I'm trying to answer these questions. Of course the abstract method doesn't have implementation. It just defines the method. But is there any other differences? Let's take an example of two classes. An abstract class and another one that inherits from it. Class diagram of an abstract class and a concrete one ? 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 // the abstract class public abstract class BaseClass { public abstract string GetAbstractValue(); public virtual string GetVirtualValue() { return "Base GetVirtualValue"; } public string GetValue() { return "Base GetValue"; } } // the concrete class public class ConcreteClass : BaseClass { public override string GetAbstractValue() { return "Concrete GetAbstractValue"; } public override string GetVirtualValue() { return "Concrete GetVirtualValue"; } public string GetValue() { return "Concrete GetValue"; } } Let's make a console application that uses the above classes. We want to make 2 instances of the concrete class. The first one should be of type BaseClass and the other one of type ConcreteClass . The client code should look like this: ? 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 class Program { static void Main(string[] args) { BaseClass instance1 = new ConcreteClass(); Console.WriteLine(instance1.GetAbstractValue()); Console.WriteLine(instance1.GetVirtualValue()); Console.WriteLine(instance1.GetValue()); ConcreteClass instance2 = new ConcreteClass(); Console.WriteLine(instance2.GetAbstractValue()); Console.WriteLine(instance2.GetVirtualValue()); Console.WriteLine(instance2.GetValue()); Console.Read(); } } Let's now see and compare the results. The results of running the application What do you conclude from the results? Let's make another experiment before conclusion. Let's remove the following 2 methods from the ConcreteClass · GetVirtualValue · GetValue Try to run the application and notice the results. The results after removing the 2 methods From the previous results we can conclude the following: Abstract Virtual No Keyword Can have implementation? No Yes Yes Can override? Must Can but not a must You can declare a new method with the same name Which keyword to use to provide new implementation in the concrete class? override override No keyword needed If an object is created of the base class type, which method will be executed? Concrete implementation The parent implementation will be called only if no implementation is provided in the concrete class Parent implementation If an object is created of the concrete class type, which method will be executed? Concrete implementation Concrete implementation The parent implementation will be called only if no implementation is provided in the concrete class

Vicky Bhatt · Answer

hello shibu, Virtual Class : A virtual class is one that has been qualified as virtual in the inheritance definition. When a derived class inherits from more than one base class, then it can inherits the members of a base class from multiple inheritance paths. If the base class is defined as virtual, only one copy of the members of the base class is inherited by the derived class irrespective of the fact that it can be inherited from a number of inheritance paths. Abstract Class : An abstract class is one, which is never instantiated. The objects of an abstract base class are never created. A base class that contains pure virtual functions is an abstract base class. A pure virtual function is a virtual function that has no implementation in its class. Thus an abstract class provides a base upon which to build other classes. It is designed only to act as a base class for other classes and it is not used to create objects. Thus an abstract base class provides some transit to the derived classes and is never initiated. Hope you can get your answer. If this will plz accept answer.

Abhay Shanker · Answer

abstract class https://msdn.microsoft.com/en-us/library/sf985hc5.aspx virtual class https://msdn.microsoft.com/en-us/library/9fkccyh4.aspx

Rajeesh Menoth · Answer

Hi, Ref the following links : 1) http://www.c-sharpcorner.com/Interviews/answer/7266/difference-between-abstract-and-virtual-functions 2) http://www.manojagarwal.co.in/difference-between-a-virtual-class-and-an-abstract-class-in-cpp/ 3) http://stackoverflow.com/questions/391483/what-is-the-difference-between-an-abstract-function-and-a-virtual-function

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