C# - Keyword usage virtual+override vs. new

Question

What are differences between declaring a method in a base type \"virtual\" and then overriding it in a child type using the \"override\" keyword as

Answer 1

virtual / override tells the compiler that the two methods are related and that in some circumstances when you would think you are calling the first (virtual) method it's actually correct to call the second (overridden) method instead. This is the foundation of polymorphism.

(new SubClass() as BaseClass).VirtualFoo()

Will call the SubClass's overriden VirtualFoo() method.

new tells the compiler that you are adding a method to a derived class with the same name as a method in the base class, but they have no relationship to each other.

(new SubClass() as BaseClass).NewBar()

Will call the BaseClass's NewBar() method, whereas:

(new SubClass()).NewBar()

Will call the SubClass's NewBar() method.