class StringUtils {

    public static boolean isEmpty(CharSequence cs) {
        return cs == null || cs.length() == 0;
    }

    public static boolean isNotEmpty(CharSequence cs) {
        return !isEmpty(cs);
    }

    public static boolean equals(CharSequence cs1, CharSequence cs2) {<FILL_FUNCTION_BODY>}
}

        if (cs1 == cs2) {
            return true;
        } else if (cs1 != null && cs2 != null) {
            if (cs1.length() != cs2.length()) {
                return false;
            } else {
                return cs1.equals(cs2);
            }
        } else {
            return false;
        }
    
<no_super_class>