Scanner sc = new Scanner (System.in);
int opcao = -1;
System.out.println("-------- CONSOLA ADMINISTRADOR -------");
System.out.println("1. Registar pessoas");
System.out.println("2. Gerir artistas, albuns e musicas");
System.out.println("3. Pesquisar musicas");
System.out.println("4. Consultar detalhes album ou artista");
System.out.println("5. Escrever critica a um album");
System.out.println("6. Dar privilegios de editor a user");
System.out.println("7. Upload de musicas");
System.out.println("0. Sair");
while (opcao != 0) {
    if (sc.hasNextInt()) {
        opcao = sc.nextInt();
        menuOp(opcao, socket);
    }
    else {
        System.out.println("Introduza um numero correto");
        sc.nextLine();
    }
}
user = user.concat("USER ");


private  void menuOp(int opcao, MulticastSocket socket){
        int op;
        Scanner sc = new Scanner (System.in);

        switch (opcao) {
            case 1:
                menuRegistarPessoas(socket);
                run();
                break;
            case 2:
                op = -1;

                System.out.println("1. Gerir artista");
                System.out.println("2. Gerir album");
                System.out.println("3. Gerir musica");

                while (op != 0) {
                    if (sc.hasNextInt()) {
                        op = sc.nextInt();
                        menuGerir(socket);
                    } else {
                        System.out.println("Introduza um numero correto");
                        sc.nextLine();
                    }
                }
            case 0:
                System.exit(0);
                break;

        }
    }

    private void menuGerir(MulticastSocket socket) {

    }

    private static void menuRegistarPessoas(MulticastSocket socket) {
        Scanner keyboardScanner = new Scanner(System.in);
        String user = "";
        String readKeyboard;

        user = user.concat("USER ");
        System.out.println("username: ");
        readKeyboard = keyboardScanner.nextLine();
        user = user.concat(readKeyboard+" ");
        System.out.println("password: ");
        readKeyboard = keyboardScanner.nextLine();
        user = user.concat(readKeyboard);

        byte[] buffer = user.getBytes();
        try {
            InetAddress group = InetAddress.getByName(MULTICAST_ADDRESS);
            DatagramPacket packet = new DatagramPacket(buffer, buffer.length, group, PORT);
            socket.send(packet);
        } catch (IOException e) {
            e.printStackTrace();
        }
    }