JavaFX Linechart ClassCastException Integer to String

Question

For a personal project I created a program which fetches stock data from markitondemand.com without any problem. In an object I store some values in a values field that is a HashMap.

Now I want to display the values of that object in a line chart in JavaFX. Currently I have the following exception:

Exception in thread "JavaFX Application Thread" java.lang.ClassCastException: java.lang.Integer cannot be cast to java.lang.String
at javafx.scene.chart.CategoryAxis.calculateRequiredSize(CategoryAxis.java:378)
at javafx.scene.chart.CategoryAxis.autoRange(CategoryAxis.java:363)
at javafx.scene.chart.Axis.computePrefHeight(Axis.java:577)
at javafx.scene.Parent.prefHeight(Parent.java:927)
at javafx.scene.layout.Region.prefHeight(Region.java:1435)
at javafx.scene.chart.XYChart.layoutChartChildren(XYChart.java:687)
at javafx.scene.chart.Chart$1.layoutChildren(Chart.java:94)
at javafx.scene.Parent.layout(Parent.java:1079)
at javafx.scene.Parent.layout(Parent.java:1085)
at javafx.scene.Parent.layout(Parent.java:1085)
at javafx.scene.Scene.doLayoutPass(Scene.java:552)
at javafx.scene.Scene$ScenePulseListener.pulse(Scene.java:2397)
at com.sun.javafx.tk.Toolkit.lambda$runPulse$31(Toolkit.java:355)
at java.security.AccessController.doPrivileged(Native Method)
at com.sun.javafx.tk.Toolkit.runPulse(Toolkit.java:354)
at com.sun.javafx.tk.Toolkit.firePulse(Toolkit.java:381)
at com.sun.javafx.tk.quantum.QuantumToolkit.pulse(QuantumToolkit.java:510)
at com.sun.javafx.tk.quantum.QuantumToolkit.pulse(QuantumToolkit.java:490)
at com.sun.javafx.tk.quantum.QuantumToolkit.lambda$runToolkit$405(QuantumToolkit.java:319)
at com.sun.glass.ui.InvokeLaterDispatcher$Future.run(InvokeLaterDispatcher.java:95)

In the stacktrace is no link to my own code, so I don't know how to solve this issue.

This is a print screen of the values that are fetched for Apple:

I loop over these values so I can add them to the series that is used as data for the line chart. Code example: (stockToDraw.getValues() returns the values displayed in the screenshot)

int i = 1;
    for(String key : stockToDraw.getValues().keySet()) {
        series.getData().add(new XYChart.Data<Number, Number>(i, stockToDraw.getValues().get(key)));
        i++;
    }

My linechart is declared as follows:

final NumberAxis xAxis = new NumberAxis();
final NumberAxis yAxis = new NumberAxis();

@FXML
LineChart<Number, Number> lineChart = new LineChart<Number, Number>(xAxis, yAxis);

XYChart.Series<Number, Number> series = new XYChart.Series<Number, Number>();

With the code samples above, I get an ClassCastException that an Integer can't be casted to a String, but I don't know how to solve this issue.

Thanks in advance!

EDIT

As being mentioned in the comments, the stacktrace referred to an CategoryAxis. This axis is includes in the FXML code as follow:

<LineChart fx:id="lineChart" layoutX="9.0" layoutY="120.0" prefHeight="470.0" prefWidth="581.0">
    <xAxis>
      <CategoryAxis label="Days" side="BOTTOM" />
    </xAxis>
    <yAxis>
      <NumberAxis label="Value" side="LEFT" />
    </yAxis>
  </LineChart>

Answer 1

As @James_D pointed out in the comments, I was initializing the linechart multiple times.

I removed the initializer and changed it to

@FXML
LineChart<String, Double> lineChart;

After that I changed XYChart.Series<Number, Number> to XYChart.Series<String, Double> in all the required places.

After this I tested in an it has the following result: