// file:   OpenListException
// author: Robert M. Keller
// purpose: Provide exception class for OpenList

/**
 * An OpenListException is thrown when an attempt is made to do something
 * illegal with an open list, such as taking first or rest of an empty list.
 * The reason for the exception is encoded as the string argument to the
 * constructor.
 * Since this class extends RuntimeException rather than just Exception,
 * it is not necessary to declare every method that might conceivably
 * throw an OpenListException.
 */

class OpenListException extends RuntimeException
{

/** The reason the exception was thrown. */

private String reason;

/**
 * Construct an OpenListException for a specified reason.
 * @param _reason the reason that the exception was thrown
 */

public OpenListException(String _reason)
  {
  reason = _reason;
  }


/**
 * Return a printable version of this exception, which states the reason
 * the exception was thrown.
 * @return printable version of this exception
 */

public String toString()
  {
  return "OpenListException: " + reason;
  }

}