code: protected void checkForPrimaryKeys(final Object realObject) throws ClassNotPersistenceCapableException
      {
          // if no PKs are specified OJB can't handle this class !
          if (m_pkValues == null || m_pkValues.length == 0)
          {
              throw createException("OJB needs at least one primary key attribute for class: ", realObject, null);
          }
  // arminw: should never happen
  //        if(m_pkValues[0] instanceof ValueContainer)
  //            throw new OJBRuntimeException("Can't handle pk values of type "+ValueContainer.class.getName());
      }
docs: OJB can handle only classes that declare at least one primary key attribute,
  this method checks this condition.
  
  @param realObject The real object to check
  @throws ClassNotPersistenceCapableException thrown if no primary key is specified for the objects class