Java Fundamentals Section----4. Transformation of objects

Object-oriented three features: encapsulation, inheritance, polymorphism

This section is the embodiment of object-oriented polymorphism

1. Upward transformation of objects

The upward transformation----assigns the object of the subclass to a reference to the parent class;

Student s = new Student ();

Person p = s;

Or it can be written

Person p = new Student ();

What members (variables and functions) can be called by a reference, depending on the data type of the application

Which method a reference invokes depends on the object to which the reference refers (the member variables and methods that are called subclasses)

2. Object-Down transformation

Transition down----Assign the object of the parent class to a reference to the subclass:

Student S1 = new Student ();

Person p = S1;

Student s2 = (Student) p;

The directly generated parent class cannot be transformed into a subclass object;

Java Fundamentals Section----4. Transformation of objects