public class BinaryTreeNode
{
   // data members
   Object element;
   BinaryTreeNode leftChild;    // left subtree
   BinaryTreeNode rightChild;   // right subtree

   // constructors
   public BinaryTreeNode() {


   }

   public BinaryTreeNode(Object theElement)
      {element = theElement;}

   public BinaryTreeNode(Object theElement,
                         BinaryTreeNode theleftChild,
                         BinaryTreeNode therightChild)
   {
       element = theElement;
       leftChild = theleftChild;
       rightChild = therightChild;
   }

   // output method
   public String toString()
      {return element.toString();}
}


/** binary tree traversal methods */

public class BinaryTreeTraversal
{


   /** preorder traversal */
   public void preOrder(BinaryTreeNode t)
   {
      if (t != null)
      {
         visit(t);                // visit tree root
         preOrder(t.leftChild);   // do left subtree
         preOrder(t.rightChild);  // do right subtree
      }
   }

   /** inorder traversal */
   public void inOrder(BinaryTreeNode t)
   {
      if (t != null)
      {
         inOrder(t.leftChild);   // do left subtree
         visit(t);               // visit tree root
         inOrder(t.rightChild);  // do right subtree
      }
   }

   /** postorder traversal */
   public void postOrder(BinaryTreeNode t)
   {
      if (t != null)
      {
         postOrder(t.leftChild);   // do left subtree
         postOrder(t.rightChild);  // do right subtree
         visit(t);                 // visit tree root
      }
   }

   /** level order traversal */
   public void levelOrder(BinaryTreeNode t)
   {
      ArrayQueue q = new ArrayQueue();
      while (t != null)
      {
         visit(t);  // visit t

         // put t's children on queue
         if (t.leftChild != null)
            q.put(t.leftChild);
         if (t.rightChild != null)
            q.put(t.rightChild);

         // get next node to visit
         t = (BinaryTreeNode) q.remove();
      }
    }

   public void visit(BinaryTreeNode t){



   }
}