Run the code:

import javafx.application.Application;
import javafx.collections.FXCollections;
import javafx.collections.ObservableList;
import javafx.event.Event;
import javafx.event.EventHandler;
import javafx.scene.Scene;
import javafx.scene.chart.PieChart;
import javafx.scene.control.*;
import javafx.scene.layout.HBox;
import javafx.scene.layout.Pane;
import javafx.scene.layout.VBox;
import javafx.stage.Stage;

public class JavaCharts extends Application {

    public static void main(String[] args) {
        launch(args);
    }
    PieChart testedPieChart = new PieChart();

    @Override
    public void start(Stage stage) throws Exception {

        ObservableList<PieChart.Data> data = FXCollections.<PieChart.Data>observableArrayList();
        for (int i = 0; i < 10; i++) {
            data.add(new PieChart.Data("Data item " + i, i * 100));
        }
        testedPieChart.setData(data);

        testedPieChart.setTitle("PieChart");
        testedPieChart.setStyle("-fx-border-color: darkgray;");
        testedPieChart.setPrefSize(300, 600);

        Pane pane = new Pane();
        pane.getChildren().add(testedPieChart);

        VBox vb = new VBox();
        vb.getChildren().addAll(pane);

        Slider slider1 = new Slider(0, 600, 300);
        slider1.setShowTickLabels(true);
        slider1.setShowTickMarks(true);
        slider1.valueProperty().bindBidirectional(testedPieChart.prefHeightProperty());
        vb.getChildren().addAll(new Label("Pref height"), slider1);

        Slider slider2 = new Slider(0, 600, 300);
        slider2.setShowTickLabels(true);
        slider2.setShowTickMarks(true);
        slider2.valueProperty().bindBidirectional(testedPieChart.prefWidthProperty());
        vb.getChildren().addAll(new Label("Pref width "), slider2);

        vb.getChildren().addAll(getAddItemHBox());
        
        pane.setPrefSize(600, 600);

        Scene scene = new Scene(vb, 700, 700);
        stage.setScene(scene);
        stage.show();
    }

    public HBox getAddItemHBox() {
        HBox hb = new HBox();
        Label lb = new Label("Add item");
        final TextField tf = TextFieldBuilder.create().prefWidth(150).build();
        Label namedLabel = new Label(" named ");
        final TextField name = TextFieldBuilder.create().prefWidth(150).build();
        Label atLb = new Label("at pos");
        final TextField tfPos = TextFieldBuilder.create().prefWidth(150).build();
        Button bt = ButtonBuilder.create().text("Add!").build();
        bt.setOnAction(new EventHandler() {

            @Override
            public void handle(Event t) {
                int index = Integer.parseInt(tfPos.getText());

                PieChart.Data newData = new PieChart.Data("".equals(name.getText()) ? String.valueOf(index) : name.getText(), Double.parseDouble(tf.getText()));

                ((PieChart) testedPieChart).getData().add(index, newData);
            }
        });
        hb.getChildren().addAll(lb, tf, namedLabel, name, atLb, tfPos, bt);
        return hb;
    }
}

Type in values:
height: 550
width: 300
Add item: 123
named:Aaaaaaaaaaaaaaa ffffffffffffffffff gggggggggggg
At pos: 2
Click button "Add"

And look at the attached movie.