code: public WritableGridFileChannel getWritableChannel(String pathname, boolean append) throws IOException {
        return getWritableChannel(pathname, append, defaultChunkSize);
     }
docs: Opens a WritableGridFileChannel for writing to the file denoted by pathname. The channel can either overwrite the
  existing file or append to it.
  @param pathname the path to write to
  @param append if true, the bytes written to the WritableGridFileChannel will be appended to the end of the file.
  If false, the bytes will overwrite the original contents.
  @return a WritableGridFileChannel for writing to the file at pathname
  @throws IOException if an error occurs