When extending another class...?

Question

I have made a BinaryTree class, tested it and everything and it all works.
Now, I have just made an AVLTree class. So, I want all the methods in the BinaryTree class to be the same as in the AVL class except the add method which I wanted to override.
So, I made the BinaryTree class abstract, and then extended the BinaryTree class in the AVL class.
So I thought that by doing this all I had to do was put in the add method and change the code and then I could use all the methods in the BinaryTree class.
Well it seems that I can, except that none of it works correctly because of private attributes. For example, my size doesn't update in my new add method and I can't figure out why. I have a private int size in both classes but it doesn't work. Not only that but my root node isn't working either.
I'll post some code here and hopefully someone knows what I'm doing wrong.
package avlTree;
* @author 383259
public class AVLTree extends BinaryTree
     private int size;
     private BSTNode root;
     private String side;
     public AVLTree()
          super();
      * @param element
     public AVLTree(Comparable element)
          super(element);
      * @param element
      * @param left
      * @param right
     public AVLTree(Comparable element, BSTNode left, BSTNode right)
          super(element, left, right);
      * @param element
      * @param left
      * @param right
     public AVLTree(Comparable element, BinaryTree left, BinaryTree right)
          super(element, left, right);
private BSTNode addToTree(Comparable o)
          try
               boolean status = false;
               if(isEmpty())
                    System.out.println("yes");
                    status = true;
                    root = new BSTNode(o);
                    size++;
                    setRoot(root);
                    return root;
               else
                    System.out.println("yes");
                    BSTNode currNode = root;
                    BSTNode newNode = new BSTNode(o);
                    while (status == false)
                         if(newNode.compareTo(currNode.getElement()) == 1)
                              if (currNode.getRight() == null)
                                   currNode.setRight(newNode);
                                   newNode.setParent(currNode);
                                   size++;
                                   side = "right";
                                   status = true;
                                   return newNode;
                              else
                                   currNode = currNode.getRight();
                         else if(newNode.compareTo(currNode.getElement()) == -1)
                              if (currNode.getLeft() == null)
                                   currNode.setLeft(newNode);
                                   newNode.setParent(currNode);
                                   size++;
                                   side = "left";
                                   status = true;
                                   return newNode;
                              else
                                   currNode = currNode.getLeft();
                         else
                              status = true;
                              return null;
                    return null;
               catch (ClassCastException cce)
                    return null;
               catch (NullPointerException npe)
                    return null;
               catch (IllegalArgumentException iae)
                    return null;
     }That private, addToTree method is actually the same as the add method in the binary tree, but is only a small part of the add method in the AVLTree. Anyway, my private root node attribute and size attribute aren't updating for some reason or another, and I cannot figure out why.

Answer 1

So, I made the BinaryTree class abstract,And you did that why exactly?
So I thought that by doing this all I had to do was
put in the add method and change the code and then I
could use all the methods in the BinaryTree class. Which is correct. Minus the private stuff, as you found out. That's what private means, after all.
Well it seems that I can, except that none of it
works correctly because of private attributes. For
example, my size doesn't update in my new add method
and I can't figure out why. I have a private int size
in both classes but it doesn't work. Not only that
but my root node isn't working either.I guess it doesn't work because you now have two size variables and constantly use the wrong one. Make size protected, or better, provide a protected setter for the size. Do the same for other private attributes you need to access.