// ---------------------------------------------------------------
// BinaryNode - Base class of all operations that act upon two
//              Node objects (+, -, *, /, ^)
// ---------------------------------------------------------------

import java.util.HashMap;
   
public abstract class BinaryNode extends Node
{
   public BinaryNode(Node left, Node right)
   {
      mLeft  = left;
      mRight = right;
   }

   // --------------------------------------------------------
   // Subclasses have to provide this method, allows us to
   // implement toString universally
   // --------------------------------------------------------

   public abstract char getSymbol();

   public String toString()
   {
      return(mLeft.toString() + " " + getSymbol() + " " + mRight.toString());
   }

   protected Node getLeft()  { return(mLeft);  }
   protected Node getRight() { return(mRight); }

   private Node mLeft; 
   private Node mRight;
}