每次我按下時，Combobox我都想從每個不同的值中刷新數據database但是我每次按下組合框時得到的是，數據會繼續增加而不是刷新截圖public void initialize(URL url, ResourceBundle rb) {        con = new DBConnect();        con.connect();        depart();    }   void init(Stage stage) {        this.stage = stage;    }    public void depart(){        String sql = "SELECT DISTINCT b.nama_bandara FROM departure as depart "                + "INNER JOIN bandara as b on b.kode_bandara = depart.kode_bandara";        try {            pst = con.conn.prepareStatement(sql);            con.rs = pst.executeQuery();            while(con.rs.next()){                combo.getItems().addAll(con.rs.getString(1));            }        } catch (SQLException ex) {            Logger.getLogger(FXMLDocumentController.class.getName()).log(Level.SEVERE, null, ex);        }    }每次我點擊，數據總是增加@FXML    private void CB(ActionEvent event) {        String depart = combo.getValue();        String sql = "SELECT b.kota, bb.kota, single.harga FROM single_trip as single \n" +                    "INNER JOIN departure as depart ON depart.kode_departure = single.kode_departure \n" +                    "INNER JOIN bandara as b on b.kode_bandara = depart.kode_bandara \n" +                    "INNER JOIN arrived as arrive on arrive.kode_arrived = single.kode_arrived \n" +                    "INNER JOIN bandara as bb on bb.kode_bandara = arrive.kode_bandara \n" +                    "WHERE b.nama_bandara = '"+depart+"'";