This product is a simple factory pattern Demo, written by objective-c 2.0。
In this Demo
HumanFactory is a factory class, to choose which class should be used.
Human is a super class, to provide a interface type of HumanFactory class method, and a class method.
Teacher is one of subclasses of Human, overide the superclass's method.
Student is another subclass of Human, overide the superclass's method as Teacher.