19.1 Polymorphism
19.2 Inclusion Polymorphism (Inheritance and Subtyping)
    19.2.1 private Visibility and Inheritance
    19.2.2 Protected Visibility
    19.2.3 Calling Methods on the Supertype
    19.2.4 Anonymous Classes
    19.2.5 Abstract Classes
    19.2.6 traits
    19.2.7 final
    19.2.8 Method Resolution
    19.2.9 Inheriting from Function Types
19.3 Inheritance in the Project
    19.3.1 Drawables
    19.3.2 Integration with Drawing
19.4 Parametric Polymorphism
    19.4.1 Parametric Types
    19.4.2 Parametric Functions and Methods
    19.4.3 Type Bounds