I want to write code, that can do following:

1. Create 9*9 GridPane board that filled with 81 StackPanes.

2. When I click on cell (StackPane) I want to change color of background StackPane to blue if it is white. If I have alreday had blue cell on board, than old cell becomes white and new one becomes blue. So, In anytime I can only have 0 or 1 colored cell.

3. I tried to use Array[9][9] of StackPanes but I failed because even if I declare this array before “public void start(Stage stage)” I fail to use each StackPane in lambda expressions or innerclasses.

4. I tried to use variable that tells if I have 1 colored cell or not and coordinates of colored cell in 2 variables. When I click on cells I see that coordinates works, but I can’t change color of Panes.

package com.example.testingcolorswitching;

import javafx.application.Application;
import javafx.fxml.FXMLLoader;
import javafx.scene.Scene;
import javafx.scene.control.Label;
import javafx.scene.layout.GridPane;
import javafx.scene.layout.StackPane;
import javafx.scene.shape.Line;
import javafx.stage.Stage;

import java.io.IOException;

public class HelloApplication extends Application {


    boolean isAnyPaneSelected = true; // true if 1 of cells is selected
    int xColored = 1; // holds X coordinate of Selected cell;
    int yColored = 1; // holds Y coordinate of Selected cell;
    int columnSize = 50;
    int rowSize = 50;

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

        GridPane grid = new GridPane();

        for (int x = 0; x < 9; x++)
            for (int y = 0; y < 9; y++){
                StackPane cell = new StackPane();
                cell.setMinSize(columnSize, rowSize);
                
                // I would like that this was checked every time I click on GridPane 
                if (isAnyPaneSelected && x == xColored && y == yColored)
                    cell.setStyle("-fx-background-color:BLUE");

                final int thisX = x;
                final int thisY = y;

                cell.setOnMouseClicked((event) -> {
                    if(isAnyPaneSelected) {
                        if (thisX == xColored & thisY == yColored)
                            isAnyPaneSelected = false;
                        else {
                            xColored = thisX;
                            yColored = thisY;
                        }
                    } else {
                        isAnyPaneSelected = true;
                        xColored = thisX;
                        yColored = thisY;
                    }

                    System.out.println(isAnyPaneSelected + " " + xColored + " " + yColored);
                });

                grid.add(cell, x, y);
            }


        // code below is not important. This code adds lines on screen.
        for (int i = 0; i <= 9; i++){
            Line line = new Line(0.0, rowSize * i, rowSize * 9, rowSize * i);
            line.setManaged(false);
            if (i % 3 == 0)
                line.setStrokeWidth(3);

            else
                line.setStrokeWidth(1);
            grid.getChildren().add(line);

            line = new Line(columnSize * i, 0.0, columnSize * i, columnSize * 9);
            line.setManaged(false);
            if (i % 3 == 0)
                line.setStrokeWidth(3);

            else
                line.setStrokeWidth(1);
            grid.getChildren().add(line);
        }

        Scene scene = new Scene(grid, 600, 600);
        stage.setScene(scene);
        stage.show();

    }

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