code: public void toFrequencyFile(String filePath) throws IOException {
          BufferedWriter writer = new BufferedWriter(new OutputStreamWriter(
                  new FileOutputStream(filePath), "UTF-8"));
          for (TrieNodeCnt child : root.children.values()) {
              child.writeFrequencies(writer, new char[0]);// recursive
          }
          writer.close();
      }
docs: one entry per line. word first, then tab, then frequency