class Strings {

    public static String concatWithString(String str, Collection<?> collection) {
        if (collection == null) return null;
        if (collection.isEmpty()) return EMPTY_STRING;
        int i = 0;
        StringBuilder sb = new StringBuilder();
        for (Object o : collection) {
            sb.append(o.toString());
            if (i < collection.size() - 1) {
                sb.append(str);
            }
            i++;
        }
        return sb.toString();
    }

    private  Strings();

}