why can not access child fields using parent reference

Question

class A {
    int super_var = 1;
}

class B extends A {
    int sub_var = 2;
}

public class Demo{
    public static void main(String []args){        
        A a = new          


        

Answer 1

You can not access B members with the reference of Parent object A.

Instead change your println statement like below to access,

System.out.print(((B)a).sub_var);