基于该example，下面的代码绘制了一个散点图，可以将双值输入到一个微调器中，并绘制在散点图上。我想在散点图上绘制一条最佳拟合线，以便计算梯度，并找到梯度值的平均值。当按下按钮时，我会将梯度值输出到文本框中。如有帮助，将不胜感激。谢谢

public class ScatterAdd extends Application {
    private final XYSeries series = new XYSeries("Voltage");

    ChoiceBox<String> domainLabels = new ChoiceBox<>();
    ChoiceBox<String> rangeLabels = new ChoiceBox<>();

    private JFreeChart createChart() {
        XYSeriesCollection dataset = new XYSeriesCollection();
        dataset.addSeries(series);

        return ChartFactory.createScatterPlot("VI Characteristics", "Current", "Voltage", dataset);
    }

    @Override
    public void start(Stage stage) {

        Image image = new Image("Grava.logo.png");
        stage.getIcons().add(image);

        ChoiceBox<String> domainLabels = new ChoiceBox<>();
        ChoiceBox<String> rangeLabels = new ChoiceBox<>();

        JFreeChart chart = createChart();
        domainLabels.getSelectionModel().selectedItemProperty().addListener((ov, s0, s1) -> {
            chart.getXYPlot().getDomainAxis().setLabel(s1);
        });
        rangeLabels.getSelectionModel().selectedItemProperty().addListener((ov, s0, s1) -> {
            chart.getXYPlot().getRangeAxis().setLabel(s1);
        });

        domainLabels.getItems().addAll("Current", "Seconds");
        domainLabels.setValue("Current");

        rangeLabels.getItems().addAll("Voltage", "Metres");
        rangeLabels.setValue("Voltage");

        var xSpin = new Spinner<Double>(-10000.000, 10000.000, 0,0.1);
        xSpin.setEditable(true);
        xSpin.setPromptText("Xvalue");

        var ySpin = new Spinner<Double>(-10000.000, 10000.000, 0,0.1);
        ySpin.setEditable(true);
        ySpin.setPromptText("Yvalue");

        var button = new Button("Add");
        button.setOnAction(ae -> series.add(xSpin.getValue(), ySpin.getValue()));

        HBox xBox = new HBox();
        xBox.getChildren().addAll(domainLabels);

        HBox yBox = new HBox();
        yBox.getChildren().addAll(rangeLabels);

        var enter = new ToolBar(xBox, xSpin, yBox, ySpin, button);
        BorderPane.setAlignment(enter, Pos.CENTER);

        BorderPane root = new BorderPane();
        root.setCenter(new ChartViewer(chart));
        root.setBottom(enter);

        stage.setTitle("ScatterAdd");
        stage.setScene(new Scene(root, 640, 480));
        stage.show();

    }

    public static void main(String[] args) {
        launch(args);
    }
}