code: public void add(char ch) {
      if (b.length <= i + EXTRA) {
        char[] new_b = new char[b.length+INC];
        for (int c = 0; c < b.length; c++)
          new_b[c] = b[c];
        b = new_b;
      }
      b[i++] = ch;
    }
docs: Add a character to the word being stemmed.  When you are finished
  adding characters, you can call stem(void) to process the word.