code: private void checkFileReopening(FileObject fileObject, boolean forWriting) throws FilerException {
          if (isInFileObjectHistory(fileObject, forWriting)) {
              if (lint)
                  log.warning("proc.file.reopening", fileObject.getName());
              throw new FilerException("Attempt to reopen a file for path " + fileObject.getName());
          }
          if (forWriting)
              fileObjectHistory.add(fileObject);
      }
docs: Check to see if the file has already been opened; if so, throw
  an exception, otherwise add it to the set of files.