code: private void fill() throws IOException {
      int i = in.read(buf, 0, buf.length);
      if (i > 0) {
        pos = 0;
        count = i;
      }
    }
docs: Fill up our buffer from the underlying input stream. Users of this
  method must ensure that they use all characters in the buffer before
  calling this method.
  
  @exception  IOException  if an I/O error occurs.