Calling an abstract method in a non-abstract method within an abstract class

Question

I have an abstract class in C#:

  public void activation()
  {
       activated = true;
       on_Activation();
  }

  protected abstract void on_Activation();

Scenario:

Assume I've made a child of the abstract class and made an implementation of the method, on_Activation() .

Questions:

• What will happen when I call Activation() in the child class?
• Will on_Activation() use the implementation of on_Activation in the child class?

Answer 1

Yes. It's a virtual method (implicitly, because it's abstract) so its "most overridden" version will be called. The fact that the call originates in a method defined on the base class makes no difference.

Answer 2

Yes. And you have just discovered polymorphism . Polymorphism means that you just call a method like on_Activation on an object (whether the current object called this , or any other object) and you do not need to specify which version of on_Activation you mean. It is the actual type of the object at runtime that decides which version of on_Activation actually gets called.

As Thomas noted, methods which behave this way are called virtual . All abstract methods are virtual in C#. So a virtual method is a name, a symbol, that can polymorphically refer to different things (different method bodies ) at runtime.

If you are curious and want to know what kind of magic is involved, you can check the details at Virtual method table . Essentially every virtual method name like on_Activation is translated as an index like n , that is the n th virtual method of this class. Every non-abstract class provides a table in which all its virtual methods bodies are specified. So, a call to on_Activation on an object is translated as a call to the n th entry in the virtual method table of the class of that object.