Inheritance without extends

Yes, inheritance means adding or changing the behavior of a class by a sub class
the traditional way of doing inheritance is by extending a class adding new methods.
Let us take an example from Java world

extending this class to add a new behavior can be done directly and easily:

But here the inheritance is static, I need to create a new class for every new functionality.
Another way of adding functionality come from Design Patterns world, it is
the Visitor Pattern which basically “represents an operation to be performed on the elements of an object structure.” but also can be utilized to define a new operation without changing the class.
One mandatory pre-requirement for this pattern is to implement it :), the implementation is adding a behavior to the class to accept the Visitor.

Visitor is an interface with single (or multiple) method(s)

Let us implement the Sub class simulator ->

But we had to add a new class for the new functionality! , Yes, but the good thing is that we can add the functionality dynamically to single objects of the class (the same idea applied in Decorator Pattern)

adding another Visitor with lambda expressions