Create a parent class, which defines a member variable,
and then create sub-categories. Subclass extends the parent class
to create the parent object, there is only numFu this member variable
parent does not know where their child in class. Subclass aware of the existence of the parent class
subclass there are two members of the variable that contains the parent class and their
The same name
Member variable parent class and subclass What happens if the same name?
Num parent class definition 100 equal
sub-class also defines num, but equal to 200
indirectly
the parent class is defined inside MehtodFu output num
where num is present among the classes, subclasses will not find downwardly
subclass define methods, output NUM
methodFu is the parent class's methods, num is the output of the parent class.
