public String stemString(String str) {

    StringBuffer result = new StringBuffer();
    int start = -1;
    for (int j = 0; j < str.length(); j++) {
      char c = str.charAt(j);
      if (Character.isLetterOrDigit(c)) {
        if (start == -1) {
          start = j;
        }
      } else if (c == '\'') {
        if (start == -1) {
          result.append(c);
        }
      } else {
        if (start != -1) {
          result.append(stem(str.substring(start, j)));
          start = -1;
        }
        result.append(c);
      }
    }
    if (start != -1) {
      result.append(stem(str.substring(start, str.length())));
    }
    return result.toString();  
  }