Purpose of Virtual method in C#

Question

Hi Everyone I would like to know what is the exact purpose of Virtual Method in C# Thanks Komathy

Ramesh Palaniappan · Answer

When an instance method declaration includes a virtual modifier that method is said to be a virtual method. When no virtual modifier is present the method is said to be a non-virtual method. The implementation of a non-virtual method is invariant: The implementation is the same whether the method is invoked on an instance of the class in which it is declared or an instance of a derived class. In contrast the implementation of a virtual method can be superseded by derived classes. The process of superseding the implementation of an inherited virtual method is known as overriding that method. In a virtual method invocation the run-time type of the instance for which that invocation takes place determines the actual method implementation to invoke. In a non-virtual method invocation the compile-time type of the instance is the determining factor. In precise terms when a method named N is invoked with an argument list A on an instance with a compile-time type C and a run-time type R (where R is either C or a class derived from C ) the invocation is processed as follows: First overload resolution is applied to C  N  and A  to select a specific method M from the set of methods declared in and inherited by C . This is described in. Then if M is a non-virtual method M is invoked. Otherwise M is a virtual method and the most derived implementation of M with respect to R is invoked. For every virtual method declared in or inherited by a class there exists a most derived implementation of the method with respect to that class. The most derived implementation of a virtual method M with respect to a class R is determined as follows: If R contains the introducing virtual declaration of M  then this is the most derived implementation of M . Otherwise if R contains an override of M  then this is the most derived implementation of M . Otherwise the most derived implementation of M with respect to R is the same as the most derived implementation of M with respect to the direct base class of R .

Bikesh Srivastava · Answer

Hi virtual method can be redefiend and also make abstarct. https://bikeshsrivastava.blogspot.in/2016/06/part-23what-is-interface-and-abstract.html

Komathy KM · Answer

Kindly have a look into the below class hierarchy If I am trying to access class “A” information from class “D” I may receive the error message that “A” created in ambiguous manner so we are unable to use this style. Because of that reason only we got a “Virtual” keyword. If we put the keyword in class A and trying to call from “D” class the runtime path will generated directly between the class A and D and we can access through that. Am I Right? Or wrong?

Rajeesh Menoth · Answer

Hi Marked public as your method. Code using System; public class Program { public static void Main( string [] args) { myChild mc = new myChild(); mc.disp(); Console.ReadLine(); } } public class myParent { public void disp() { Console.WriteLine( Hi ); } } public class myChild : myParent { public void disp() { Console.WriteLine( Hello ); } } Reference : https://dotnetfiddle.net/xocFci

Komathy KM · Answer

Hi Everyone Kindly look the below mentioned program. class Program { static void Main(string[] args) { myChild mc = new myChild(); mc.disp(); Console.ReadLine(); } } class myParent { public void disp() { Console.WriteLine(Hi); } } class myChild : myParent { public void disp() { Console.WriteLine(Hello); } } According to my understanding if I tried to call the disp() method from the base class object it should invoke the disp() method of the myChild class but it won't. Kindly tell me where I went wrong? Moreover without using virtual and override keyword I am able to do the method overriding. Then why I need all the keywords? Thanks in Advance

Rajeesh Menoth · Answer

Hi Code using System; public class Program { class A { public virtual void Test() { Console.WriteLine( A::Test() ); } } class B : A { public override void Test() { Console.WriteLine( B::Test() ); } } public static void Main() { A a = new A(); B b = new B(); b.Test(); } } Virtual : A virtual method can be redefined. The virtual keyword designates a method that is overridden in derived classes. We can add derived types without modifying the rest of the program. The runtime type of objects thus determines behavior. Reference : http://www.dotnetperls.com/virtual Demo : https://dotnetfiddle.net/kX0ZL4

Vinay Singh · Answer

virtual function(method) : A virtual method is the method which is declared with the keyword virtual and it can be overridden by the derived class method by using override keyword. Its unto the derived class weather to override it or not. There are nothing call virtual class in C#. http://www.dotnetperls.com/virtual

Midhun T P · Answer

Hi Please go through below links. You will get clear idea about virtual method - http://www.c-sharpcorner.com/UploadFile/3d39b4/virtual-method-in-C-Sharp/ http://www.dotnetperls.com/virtual http://programcall.com/26/csnet/virtual-methods-in-csnet-with-example.aspx