Inheritance
Notes on Inheritance (First set)
    - Inherited state and methods are not repeated in subclass.
- Subclass constructor invokes superclass constructor with
    super()"method" to initialize inherited state.
- A redefined method (same signature, new body)
    overrides method from superclass; redefined
    method is executed instead.
    - private: instance variables & methods cannot be
    accessed/used directly by the subclass
- public: can be accessed/used by subclass (or anyone)
- protected: accessible to class and
    its subclasses, but not to other classes (new keyword)
Alyce Brady, Kalamazoo College