code: public Object selectElement(String predicate) throws org.odmg.QueryInvalidException
      {
          return ((DList) this.query(predicate)).get(0);
      }
docs: Selects the single element of the collection for which the provided OQL query
  predicate is true.
  @param	predicate	An OQL boolean query predicate.
  @return The element that evaluates to true for the predicate. If no element
  evaluates to true, null is returned.
  @exception	org.odmg.QueryInvalidException	The query predicate is invalid.