nick = new JTextField("nick", 5);
    add(nick);
    nick.addFocusListener(new FocusListener() {
        public void focusGained(FocusEvent e) {
            nick.setText("");

        }

        public void focusLost(FocusEvent e) {
            // nothing
        }
    });

    JLabel texto = new JLabel("CLIENTE");
    add(texto);

    ip = new JTextField("Introduce la IP del destinatario", 16);
    add(ip);
    ip.addFocusListener(new FocusListener() {
        public void focusGained(FocusEvent e) {
            ip.setText("");

        }

        public void focusLost(FocusEvent e) {
            // nothing
        }
    });