JavaFx handleEvent function not updating the variables stored in other class

Question

I am building a UI for user input and another UI for displaying histogram. I have developed two UIs and tested them separately. Each works perfectly, but when I try to compile them together, an error occurs.

This is the file for histogramController:

The following file has two scenes where I need to switch between the scenes.

public class HistogramController extends Application {
    
    private Scene scene;
    private Parent root;
    int histogramSize ;
    int bin;
    int [] histArr;
    int  temp;
    int[] cutoffs = new int[bin+1];
    int[] counts = new int[bin];

public void start(Stage stage) throws IOException {
    //the UI to prompt user input
    root = FXMLLoader.load(getClass().getResource("hello-view.fxml"));
    scene = new Scene(root , 503, 547);
    stage.setScene(scene);
    stage.show();

}

// the UI for histogram
public void createStage1(){
    Stage primaryStage = new Stage();
    Calculation();
    Label labelInfo = new Label();

    final CategoryAxis xAxis = new CategoryAxis();
    final NumberAxis yAxis = new NumberAxis();
    final BarChart<String,Number> barChart = new BarChart<>(xAxis,yAxis);
    barChart.setCategoryGap(0);
    barChart.setBarGap(0);

    xAxis.setLabel("Range of Number of Passengers at 5min interval");
    yAxis.setLabel("Number of Data point(s)")


    XYChart.Series series1 = new XYChart.Series();

    Scene scene = new Scene(root, 800, 450);

    primaryStage.setTitle("WIA1002 HISTOGRAM");
    primaryStage.setScene(scene);
    primaryStage.show();
}

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

//calculation for the histogram

private void Calculation(){

    //find required data
    int min = histArr[0];
    int max = histArr[histogramSize-1];
    int increment = (max - min) / bin;
    temp = min;
    int counter = 0;

    //find cutoffs
    while (temp <= max) {
        cutoffs[counter] = temp;
        temp += increment;
        counter++;
    }

    temp = 1;
    int nextBin = cutoffs[temp];
    counter = 0;

    //find counts
    for (int j = 0; j < histogramSize; j++) {
        if (histArr[j] < nextBin)
            counter++;
        else {
            temp++;
            if (temp == cutoffs.length) {
                counts[temp-2] = ++counter;
                break;
            }

            counts[temp-2] = counter;
            counter = 1;
            nextBin = cutoffs[temp];
        }
    }
}

}

Apparently, I need input from user and store the values in the (histogramSize, bin, histArr ) variables in HistogramController class.

This is my input controller class.

public class InputController {

        @FXML
        private TextField bin;

        @FXML
        private TextField hist;

        @FXML
        private TextField size;


        public void submit(javafx.event.ActionEvent actionEvent) throws IOException {
                HistogramController input = new HistogramController();
                input.histogramSize = Integer.parseInt(size.getText());
                input.bin = Integer.parseInt(bin.getText());
                String [] hists = hist.getText().split(", ");
                input.histArr = new int [hists.length];
                for (int y = 0; y< hists.length;y++) {
                        input.histArr[y] = Integer.parseInt(hists[y]);
                }

                FXMLLoader loader = new FXMLLoader(getClass().getResource("graph.fxml"));
                Parent root = loader.load();
                input.createStage1();
        }
}

I want my program to display the histogram after user clicked the submit button. However, when I clicked the submit button, it shows me this error.

Exception in thread "JavaFX Application Thread" java.lang.RuntimeException: java.lang.reflect.InvocationTargetException
Caused by: java.lang.reflect.InvocationTargetException
Caused by: java.lang.ArrayIndexOutOfBoundsException: Index 0 out of bounds for length 0
    at com.example.histograms.HistogramController.Calculation(HistogramController.java:90)
    at com.example.histograms.HistogramController.createStage1(HistogramController.java:41)
    at com.example.histograms.InputController.submit(InputController.java:36)

I think this error is caused by I have a null histArr, bin and size, meaning the user input is not able to store in the variables in my HistogramController class. I need my program to receive the input from user and update the array immediately to output the histogram.