如何访问超出类范围的变量？

我正在尝试编写JavaFX Sudoku程序，用户可以通过以下方法填充单元格：

1. 单击九个按钮之一（对应于1-9）
2. 单击其中一个单元格

代码的工作方式是：单击按钮时，将与该按钮对应的int分配给selectedNum。当单击单元格时，单元格将其文本分配给selectedNum。但是，这就是问题所在–在构造函数内部实现setOnAction函数Cell。Cell无法访问selectedNum。如果它是超出类范围的变量，如何传递selectedNum？

单元格类别：

import javafx.event.EventHandler;
import javafx.scene.Node;
import javafx.scene.input.MouseEvent;
import javafx.scene.layout.StackPane;
import javafx.scene.paint.Color;
import javafx.scene.shape.Rectangle;
import javafx.scene.text.Font;
import javafx.scene.text.Text;

/**
 * The Cell class inherits StackPane, representing one of the cells in Sudoku.
 * @author rkuni
 *
 */
public class Cell extends StackPane{
    
    private Text text; //displays the number inside the cell
    private Rectangle rect; //visual element for the cell
    
    /**
     * Default Constructor for Cell
     */
    public Cell() {
        text = new Text("");
        text.setFont(Font.font(30));
        rect = new Rectangle(50, 50);
        rect.setStyle("-fx-fill: white; -fx-stroke: black; -fx-stroke-width: 1;");
        this.getChildren().add(rect);
        this.getChildren().add(text);
        
        this.setOnMouseClicked(new EventHandler<MouseEvent>() { 
            @Override
            public void handle(MouseEvent t) {
                text.setText("" + 1); //when clicked, I want to set text to the number that is selected.
            }
        });
    }
}

主班

import javafx.application.Application;
import javafx.event.ActionEvent;
import javafx.event.EventHandler;
import javafx.stage.Stage;
import javafx.scene.Group;
import javafx.scene.Scene;
import javafx.scene.control.Button;
import javafx.scene.layout.BorderPane;
import javafx.scene.text.Font;

public class Main extends Application {
    
    private int selectedNum = 0;
    
    @Override
    public void start(Stage primaryStage) {
        try {
            
            Group root = new Group();
            Cell cell1 = new Cell();
            cell1.setLayoutX(100);
            cell1.setLayoutY(100);
            root.getChildren().add(cell1);
            
            Button numSelection[] = new Button[9];
            for (int i = 0; i < 9; i++) {
                final int j = i; 
                numSelection[i] = new Button("" + (i + 1));
                numSelection[i].setLayoutY((i / 3) * 55 + 200);
                numSelection[i].setLayoutX((i % 3) * 55 + 630);
                numSelection[i].setMinHeight(50);
                numSelection[i].setMinWidth(50);
                numSelection[i].setFont(Font.font(20));
                root.getChildren().add(numSelection[i]);

                numSelection[i].setOnAction(new EventHandler<ActionEvent>() {
                    @Override
                    public void handle(ActionEvent arg0) {
                        selectedNum = j + 1;
                    }
                });
            }
            
            Scene scene = new Scene(root,900,500);
            primaryStage.setScene(scene);
            primaryStage.show();
            
        } catch(Exception e) {
            e.printStackTrace();
        }
    }
    
    public static void main(String[] args) {
        launch(args);
    }
}

潜在解决方案

潜在的解决方案是根本没有Cell类，并且代码将起作用。问题不再存在，因为所有变量都在同一范围内。但是，我想保留Cell类，因为它使代码更有条理。无论如何，这里：

import javafx.application.Application;
import javafx.event.ActionEvent;
import javafx.event.EventHandler;
import javafx.stage.Stage;
import javafx.scene.Group;
import javafx.scene.Scene;
import javafx.scene.control.Button;
import javafx.scene.input.MouseEvent;
import javafx.scene.layout.StackPane;
import javafx.scene.paint.Color;
import javafx.scene.shape.Rectangle;
import javafx.scene.text.Font;
import javafx.scene.text.Text;


public class Main extends Application {
    
    private int selectedNum; //will take the value of the last pressed button (1-9)
    
    @Override
    public void start(Stage primaryStage) {
        try {
            Group root = new Group();
            
            //setting up a stackpane that will contain a rect and text, making for a "cell"
            StackPane stack1 = new StackPane();
            Text text1 = new Text("");
            Rectangle rect1 = new Rectangle(50,50);
            rect1.setStyle("-fx-fill: white; -fx-stroke: black; -fx-stroke-width: 1;");
            stack1.getChildren().add(text1);
            stack1.getChildren().add(rect1);
            stack1.setLayoutX(100);
            stack1.setLayoutY(100);
            stack1.setOnMouseClicked(new EventHandler<MouseEvent>() { 
                @Override
                public void handle(MouseEvent t) {
                    text1.setText("" + selectedNum); //when clicked, set text to the number that is selected.
                }
            });
            
            //setting up the buttons that will designate which number will go into the cell.
            Button numButtons[] = new Button[9];
            for (int i = 0; i < 9; i++) {
                final int j = i;
                numButtons[i] = new Button("" + (i + 1));
                numButtons[i].setLayoutY((i / 3) * 55 + 200);
                numButtons[i].setLayoutX((i % 3) * 55 + 630);
                numButtons[i].setMinHeight(50);
                numButtons[i].setMinWidth(50);
                numButtons[i].setFont(Font.font(20));
                root.getChildren().add(numButtons[i]);

                numButtons[i].setOnAction(new EventHandler<ActionEvent>() {
                    @Override
                    public void handle(ActionEvent arg0) {
                        selectedNum = j + 1;
                    }
                });
            }
            
            text1.toFront();
            root.getChildren().add(stack1);
            Scene scene = new Scene(root,900,500);
            primaryStage.setScene(scene);
            primaryStage.show();
            
        } catch(Exception e) {
            e.printStackTrace();
        }
    }
    
    public static void main(String[] args) {
        launch(args);
    }
}

我还考虑过重写该函数以添加参数，但尚未使它成功工作。