public class Package {
    public String checksum() { return "Package"; }

    public static void main(String []args) {
        Comm c = new Comm();
        System.out.println(c.send((Package)new UDP()) + "; "
                        + c.send(new TCP()) + "; "
                        + c.send(new UDP()));
    }
}

class UDP extends Package {
    public String checksum() { return "UDP"; }
}

class TCP extends Package {
    public String checksum() { return "TCP"; }
}

class Comm {
    String send(Package p) { return "PKG:" + p.checksum(); }
    String send(UDP p) { return "UDP:" + p.checksum(); }
    String send(TCP p) { return "TCP:" + p.checksum(); }
}