docs: public synchronized void resizeFile(int newsize) throws IOException {
      if (!writable) {
        throw new IOException("File is not writeable!");
      }
      // update the number of records
      this.numrecs = newsize;
      file.seek(HEADER_POS_SIZE);
      file.writeInt(numrecs);
  
      // resize file
      file.setLength(indexToFileposition(numrecs));
      mapArray();
    }