code: private void checkFileReopening(FileObject fileObject, boolean addToHistory) throws FilerException {
          for(FileObject veteran : fileObjectHistory) {
              if (fileManager.isSameFile(veteran, fileObject)) {
                  if (lint)
                      log.warning("proc.file.reopening", fileObject.getName());
                  throw new FilerException("Attempt to reopen a file for path " + fileObject.getName());
              }
          }
          if (addToHistory)
              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.