code: @NotNull
      @Deprecated
      public static List<String> extractNGrams(@NotNull CharSequence text, @Nullable Filter filter) {
          List<String> list = new ArrayList<>();
          NGram ngram = new NGram();
          for(int i=0;i<text.length();++i) {
              ngram.addChar(text.charAt(i));
              for(int n=1;n<=NGram.N_GRAM;++n){
                  String w = ngram.get(n);
                  if (w!=null) { //TODO this null check is ugly
                      if (filter==null || filter.use(w)) {
                          list.add(w);
                      }
                  }
              }
          }
          return list;
      }
docs: This was the method found in the <i>com.cybozu.labs.langdetect.Detector</i> class, it was used to extract
  grams from the to-analyze text.
  
  NOTE: although it adds the first ngram with space, it does not add the last n-gram with space. example: "foo" gives " fo" but not "oo "!.
  It is not clear yet whether this is desired (and why) or a bug.
  
  TODO replace this algorithm with a simpler, faster one that uses less memory: only by position shifting. also, the returned list size
  can be computed before making it (based on text length and number of n-grams).