Local variables and member variables also have duplicate names
how to distinguish three kinds of problem variables of the same name as
the new parent
and then a new subclass inherits the parent class
the parent class has 10 equal num
subclasses have 20 equal num
subclass definition is equal to the local variable Num 30
so there should be three num. A parent num. Subclass num. There is a local variable num subclass
super
In a subclass I wanted to visit here and if num parent class is how to access the 10? Here introduce a new keyword super
distinguish three
