Array Object Question

[Edward Lawrence]

Given the following 3 classes Animal, Dog, and Array in 3 separate files, I compiled them and ran only the Array class with
the following results:
line 42 output: protected Animal instance variable i = 1
line 46 output: Dog element = pkgb.Dog@45a877

My Questions:
1. Why wouldn't line 48 compile without the cast when line 42 did not need one?
2. why does line 50 produce a compile error without the "//" but line 42 seems to run the
Dog initialization block without errors?

 
package pkga;

public class Animal {

        public int p = 3;
        private int v = 4;
        protected int i = 1;
        int j = 2;
}



package pkgb;

import pkga.Animal;

public class Dog extends Animal {

   public int fromAnimal = i;

   {
        System.out.println("protected Animal instance variable i = " + i);
   }


}
 

import pkga.*;
import pkgb.*;

public class Array{
        Animal [] an = new Animal [3];

        public static void main(String[] args)
        {
             Array ar = new Array();
               
             for(int x=0;x<ar.an.length;x++){
                  if(x==0){
                       ar.an[x]=new Dog();
                  }
             }

             System.out.println("Dog element = " + ar.an[0]);

             Dog dog = (Dog)ar.an[0];

            //System.out.println("Dog cast from Animal array i = " + dog.i);
        }
}

[Rob Spoor]

Edward Lawrence wrote:1. Why wouldn't line 48 compile without the cast when line 42 did not need one?

Because one is upcasting and the other is downcasting.

2. why does line 50 produce a compile error without the "//" but line 42 seems to run the Dog initialization block without errors?

Because Animal's "i" is protected, which means it can only be accessed from subclasses of Animal or classes in the same package as Animal. Since your Array class is neither it cannot access dog.i.

[Edward Lawrence]

This is just to very and understand better.
When I created the reference in the array to the Dog object I was implicitly downcasting. Am I correct?

Another clarification / Question
So what is the function of the element I am using on line 48 to create the new Dog object?
Does that element point to a Dog or in reality to an Animal?
In other words I do not quite understand the statement on line 48 although I authored it. Please elaborate a little more for
greenhorn Edward Lawrence.

[Edward Lawrence]

Just wanted to add this if I remember correctly. When compiling, the compiler thinks sees the element as an Animal and not a Dog. Am I correct?