code: private String englishLanguageFirstSentence(String s) {
          if (s == null) {
              return null;
          }
          int len = s.length();
          boolean period = false;
          for (int i = 0 ; i < len ; i++) {
              switch (s.charAt(i)) {
                  case '.':
                      period = true;
                      break;
                  case ' ':
                  case '\t':
                  case '\n':
              case '\r':
              case '\f':
                      if (period) {
                          return s.substring(0, i);
                      }
                      break;
              case '<':
                      if (i > 0) {
                          if (htmlSentenceTerminatorFound(s, i)) {
                              return s.substring(0, i);
                          }
                      }
                      break;
                  default:
                      period = false;
              }
          }
          return s;
      }
docs: Return the first sentence of a string, where a sentence ends
  with a period followed be white space.