// ChartController.java
public void displayChart() {

// XYChart.Series series = new XYChart.Series();
// series.getData().add();

    lineChart.getData().add(series);

    chartField.setContent(lineChart);
}

// Main.java
 public void start(Stage primaryStage) throws IOException {

        display();

        ChartController chartController = new ChartController();
        chartController.setMain(this);
        chartController.setStage(primaryStage);
        chartController.displayChart();

}

 private void display() {
        try {
            FXMLLoader fl = new FXMLLoader();
            fl.setLocation(getClass().getResource("/OverView.fxml"));

            AnchorPane anchorPane = fl.load();

            Scene scene = new Scene(anchorPane);
            stage.setScene(scene);
            stage.show();
        } catch (IOException e) {
            e.printStackTrace();
        }