Difference between virtual and override in C#

In C#, both virtual and override are keywords used in the context of method overriding, a fundamental concept in object-oriented programming that allows a subclass to provide a specific implementation of a method that is already defined in its superclass. Here's the difference between virtual and override:

1. virtual keyword:

   • When you declare a method with the virtual keyword in the base class, you indicate that the method can be overridden by derived classes.
   • The virtual keyword allows the method in the base class to be redefined in derived classes.
   • Methods marked as virtual provide a default implementation in the base class, but derived classes can choose to override this method with their own implementation.
   • Example:

     public class BaseClass
     {
         public virtual void MyMethod()
         {
             Console.WriteLine("Base class implementation");
         }
     }
     

2. override keyword:

   • When you override a method in a derived class, you use the override keyword to indicate that you are providing a new implementation for a method that is already defined in the base class.
   • You must use the override keyword in the derived class to indicate that you are intentionally overriding a virtual method from the base class.
   • The method signature (name, return type, and parameters) in the derived class must match exactly with the method signature in the base class.
   • Example:

     public class DerivedClass : BaseClass
     {
         public override void MyMethod()
         {
             Console.WriteLine("Derived class implementation");
         }
     }
     

In summary, virtual allows a method in a base class to be overridden in derived classes, while override is used in the derived class to indicate that it is intentionally overriding a method from the base class. Together, these keywords facilitate polymorphism and dynamic method invocation in object-oriented programming.