public static KeyableCharSet createFor(final String chars) {
        if (chars == null) {
            return EMPTY;
        }
        final List<Character> cList = new ArrayList<>();
        for (char c : chars.toCharArray()) {
            cList.add(c);
        }
        return new KeyableCharSet(cList);
    }
A charset identifiable by a string key. The later can be used e.g. for caching purposes
main/src/main/java/cgeo/geocaching/utils/KeyableCharSet.java