The upward and downward transformation of polymorphism

The program has been written with Animal Class and Pig class , among Animal Class only shout Method
Save the information as follows

Memory analysis

If you have to access the rest of the methods 、 attribute

public class Demo {
    
    // This is a main Method , It's the entrance to the program ：
    public static void main(String[] args) {
    
        Pig p = new Pig();
        Animal an = p;// The transformation of ： Upward transformation 
        an.shout();
        // Add transformation code ：
        // take Animal To Pig type ：
        Pig pig = (Pig)an ;// The transformation of ： Move down 
        pig.eat();
        pig.age = 10;
        pig.weight = 60.8;
    }
}

Corresponding to the memory

Before thinking equals Method