Base class and subclass [Notes]

1. If you use a "base class Pointer" to point to a "derived class Object", you can only call the functions defined by the base class through this pointer.
2. if you use a "derived class Pointer" to point to a "base class Object", you must first perform an explicit Transformation Operation (explicit cast). This method is dangerous and does not conform to real life experience. ProgramThe design will also bring confusion to programmers.
3. if both the base class and the derived class define "member functions with the same name", which function should be called when a member function is called through an object pointer, the pointer must be of the original type, rather than the type of the object actually referred to by the pointer. this is essentially the same as the first point.