1. Polymorphic definition:
1.There must be an inheritance relationship.
2.There must be a way to rewrite.
3.The parent class refers to a subclass object.
Two, the characteristics of member access in polymorphism (parent f = new child).
A：Member variables: compile the left side, run to the left;
B：Constructor: When creating subclass objects, access the constructor of the parent class and initialize the data of the parent class.
C：Member method: compile the left side, run to the right.
D：Static method: compile the left side, run to the left.
Three. The role of polymorphism.
1.Improved code maintainability.
2.Too high the scalability of the code.