Písmena

public class FXMLDocumentController implements Initializable {

    @FXML
    private ListView<String> listView;

    @FXML
    private PieChart graf;
    ObservableList<PieChart.Data> pieChartData;
    ObservableList<String> retezce;

    @Override
    public void initialize(URL url, ResourceBundle rb) {
        retezce = FXCollections.observableArrayList();
        listView.setItems(retezce);

    }

    @FXML
    private void konecButton(ActionEvent event) {
    }

    @FXML
    private void pridejButton(ActionEvent event) {
        TextInputDialog dialog = new TextInputDialog();
        dialog.setTitle("PŘIDÁNÍ");
        dialog.setContentText("Zadejte String pro přidání do LISTVIEW");

        Optional<String> res = dialog.showAndWait();

        res.ifPresent(text -> retezce.add(text));
        listView.refresh();

        aktualizujGraf();
    }

    @FXML
    private void odeberButton(ActionEvent event) {
        String s = listView.getSelectionModel().getSelectedItem();

        retezce.remove(s);
        listView.refresh();

        if (Objects.nonNull(retezce)) {
            aktualizujGraf();
        } else {
            graf.getData().clear();
        }

    }

    @FXML
    private void odebetVseButton(ActionEvent event) {
        odeberVse();
    }

    @FXML
    private void ulozButton(ActionEvent event) throws IOException {
        if (Objects.nonNull(retezce)) {
            File file = new File("retezce.txt");
            BufferedWriter bw = new BufferedWriter(new FileWriter(file));

            for (String s : retezce) {
                bw.write(s);
                bw.newLine();
            }

           bw.close();
        }

    }

    @FXML
    private void nactiButton(ActionEvent event) throws FileNotFoundException, IOException {
        FileChooser fc = new FileChooser();
        fc.getExtensionFilters().addAll(new FileChooser.ExtensionFilter("txt", "*.txt"),
                new FileChooser.ExtensionFilter("all", "*.*"));
        File file = fc.showOpenDialog(IPOG_Zkouska_12.stage);
        String line;
        if (Objects.nonNull(file)) {
            if (Objects.nonNull(retezce)) {
                odeberVse();
                BufferedReader br = new BufferedReader(new FileReader(file));
                while ((line = br.readLine()) != null) {
                    if (!line.equals("")) {
                        retezce.add(line);
                    }

                }
                br.close();
                aktualizujGraf();
            }
        }


    }

    private void aktualizujGraf() {
        int pole[] = new int[123];
        for (int i = 0; i < pole.length; i++) {
            pole[i] = 0;
        }

        if (Objects.nonNull(retezce)) {
            int pom;
            for (String s : retezce) {
                for (int i = 0; i < s.length(); i++) {
                    pom = s.charAt(i);
                    pole[pom]++;
                }
            }


            pieChartData = FXCollections.observableArrayList();

            for (int i = 0; i < pole.length; i++) {
                if (pole[i] != 0) {
                    char ch = (char) i;
                    String s = String.valueOf(ch);
                    pieChartData.add(new PieChart.Data(s + " " + "(" + Integer.toString(pole[i]) + ")", pole[i]));
                }
            }

            graf.setLegendSide(Side.RIGHT);
            graf.setData(pieChartData);
        }

    }

    void odeberVse() {
        if (Objects.nonNull(retezce)) {
            retezce.clear();
        listView.getItems().clear();
        //pieChartData.clear();
        //graf.getData().clear();
        }

    }