/** An interface used in the Node class to ensure that
 *  an object has an operateOn method.
 *
 *  Taken from Core Web Programming from 
 *  Prentice Hall and Sun Microsystems Press,
 *  http://www.corewebprogramming.com/.
 *  © 2001 Marty Hall and Larry Brown;
 *  may be freely used or adapted. 
 */

public interface NodeOperator {
  void operateOn(Node node);
}