code: public boolean checkCall (String warning)
      {
          if (_firstCall == null) {
              _firstCall = new Exception(
                  "---- First call (at " + _format.format(new Date()) + ") ----");
              return false;
          }
  
          log.warning(warning, new Exception());
          log.warning("First call:", _firstCall);
          return true;
      }
docs: This method should be called when the code passes through the code
  path that should be called only once. The first time through this
  path, the method will return false and record the stack trace.
  Subsquent calls will log an error and report the current and
  first-time-through stack traces.
  
  @param warning the warning message to issue prior to logging the
  two stack traces.