public void FillComboboxLibro_Autor() {
        try {
            con = DriverManager.getConnection("jdbc:mysql://localhost:3306/sistemabliblio1?autoReconnect=true&useSSL=false", "root", "");
            String sql = "SELECT * FROM autor";
            pst = con.prepareStatement(sql);
            rs = pst.executeQuery();
            while (rs.next()) {
                String a = rs.getString("nombre");
                String b = rs.getString("apeliidoPaterno");
                String c = rs.getString("apellidoMaterno");
                libro_autor.addItem(a+" "+b+" "+c);
            }
        } catch (Exception ex) {
            JOptionPane.showMessageDialog(null, ex);
        }
    }