Classes and Inheritance - Illustrated C# 2005 - page 149

The following code is the same as in the previous section, but this time, the methods are
labeled virtual and override . This produces a result that is very different from that of the pre-
vious example. In this version, calling the method through the base class invokes the method
in the derived class.

class MyBaseClass {
virtual public void Print()
{
Console.WriteLine("This is the base class.");
}
}

class MyDerivedClass : MyBaseClass {
override public void Print()
{
Console.WriteLine("This is the derived class.");
}
}

class Program {
static void Main()
{
MyDerivedClass derived = new MyDerivedClass();
MyBaseClass mybc = (MyBaseClass)derived;
↑
derived.Print(); Cast to base class
mybc.Print();
}
}

This code produces the following output:

This is the derived class.
This is the derived class.

Other important information about the virtual and override modifiers is the following:

￿ The overriding and overridden methods must have the same accessibility. In other

words, the overridden method cannot be, for example, private , and the overriding
method public .

You cannot override a method that is static or is non-virtual. ￿

￿ Methods, properties, and indexers (which I covered in the preceding chapter), and

another member type, called events (which I will cover later in the text), can all be
declared virtual and override .