public static String firstLast(String a, String b) {

    String result;
    String aChar;
    String bChar;

    if (a.length() == 0)
        aChar = "$";
    else
        aChar = a.substring(a.length() - 1);

    if (b.length() == 0)
        bChar = "$";
    else
        bChar = b.substring(0, 1);

    result = aChar + bChar;
    return result;
}