我正在为我的课堂使用Java在JGrasp中制作一个魔术8球。如何使代码运行？我不知道我的错误是什么，也不知道如何修正它？

Question

这是我的密码

import java.util.*;
import javafx.application.Application;
import javafx.scene.Scene;
import javafx.scene.layout.Pane;
import javafx.scene.layout.StackPane;
import javafx.stage.Stage;
import javafx.scene.shape.Circle;
import javafx.scene.shape.Rectangle;
import javafx.scene.shape.Polygon;
import javafx.scene.paint.Color;
import javafx.scene.text.Text;
import javafx.scene.image.ImageView;
import javafx.scene.image.Image;
import javafx.scene.text.Font;
import javafx.scene.text.FontWeight;
import javafx.geometry.Pos;
import javafx.scene.layout.VBox;
import javafx.scene.control.Button;
import javafx.scene.layout.FlowPane;
import javafx.geometry.Pos;
import javafx.scene.control.TextField;
import java.security.SecureRandom;
import javax.swing.ImageIcon;
import javax.swing.JOptionPane;

   public class FinalProject8ball extends Application
   {
      @Override
      public void start(Stage primaryStage)
      {
         Circle circle = new Circle(80);
         circle.setStroke(Color.BLACK);
         circle.setFill(Color.BLACK);

         StackPane sPane = new StackPane();
         sPane.getChildren().add(circle);

         Scene scene = new Scene(sPane, 300, 400);
         primaryStage.setScene(scene);
         primaryStage.show();       
         Polygon triangle = new Polygon();
         triangle.getPoints().setAll(
            50.0, 50.0,
            60.0, 60.0,
            20.0, 40.0
            );

         StackPane sPane1 = new StackPane();
         sPane1.getChildren().add(triangle);

         Scene scene2 = new Scene(sPane, 300, 400);
         primaryStage.setScene(scene2);
         primaryStage.show();

         String answers[] = {"It is certain", "It is decidedly so", "Without a doubt",
            "Yes - definitely", "You may rely on it", "As I see it, yes",
            "Most likely", "Outlook good", "Signs point to yes",
            "Yes", "Reply hazy, try again", "Ask again later",
            "Better not tell you now", "Cannot predict now", "Concentrate and ask again",
            "Don't count on it", "My reply is no", "My sources say no",
            "Outlook not so good", "Very doubtful"};

        //constructs a random number  
         SecureRandom randomNumber = new SecureRandom();
         ImageIcon image = new ImageIcon("magic8ball.jpg");
         int counter = 0;

        //the loop keeps asking the person to plat till no button is clicked
         while(!(counter == 1)) {
            //prompts the user to ask a yes or no question 
            String answer = JOptionPane.showInputDialog(null, 
                    "PLease enter a yes or no question:", 
                    "WELCOME: What will your answer be?!", JOptionPane.INFORMATION_MESSAGE);

            //displays the answer
            if(answer != null)
               JOptionPane.showMessageDialog(null, answer+ "\n" + answers[randomNumber.nextInt(answers.length)], 
                  "The Magic-8 Ball has responded.", JOptionPane.PLAIN_MESSAGE, image);

            //gives the user the option to click yes or no to continue or end the program
            counter = JOptionPane.showConfirmDialog(null, "", "Would you like to ask again?", 
                    JOptionPane.YES_NO_OPTION, 0, image);                           
         }

        //displays my name after user enters no to give credit
         JOptionPane.showMessageDialog(null, "Created by Isabelle", "Have a MAGICAL day! Your answers have been answerd.", 
                JOptionPane.PLAIN_MESSAGE, image);
      }
      public static void main(String[] args)
      {
         Application.launch(args);
         }
      }

这是我在编译完代码后尝试运行代码后得到的错误消息。

----jgrast exec：Java--module-path C:\users\Isabelle Rose\download\openjfx-11.0.2_windows-x64_bin-sdk(1)\javafx-sdk-11.0.2\lib--add-modules=javafx.controls应用程序中的FinalProject8ball异常启动方法java.lang.reflect.invocationtargetexception在java.base/jdk.internal.reflect.nativeMethodAccessorImpl.Invoke0（本机方法）在）java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.Invoke(DelegatingMethodAccessorImpl.java:43)在java.base/java.lang.reflect.method.Invoke(method.java:566)在java.base/sun.launcher.launcherHelper$fxhelper.main(launcherhelper.java:1051)所致：java.lang.RuntimeException：在stene.setroot(scene.Java:1178)在javafx.graphics/javafx.scene.scene.（scene.Java:356)在javafx.graphics/javafx.scene.scene.（scene.Java:236）在finalproject8ball.start(finalproject8ball.Java:58)在javafx.graphics/com.sun.javafx.application.launcherimpl.lambda$launchapplication1$9(launcherimpl.Java:846)在InalProject8Ball

Answer 1

堆栈中的真正错误如下：

Caused by: java.lang.IllegalArgumentException: StackPane@70ea261c[styleClass=root]is already set as root of another scene

看这一行：

Scene scene2 = new Scene(sPane, 300, 400);

请尝试以下操作：

// You already used 'sPane' as the root of a previous scene called 'scene'
Scene scene2 = new Scene(sPane1, 300, 400);

注：

虽然您的程序将运行与这一个单一的变化，我认为，您将发现它看起来不是它应该的方式。您使用的是两个StackPane，一个是圆形，另一个是三角形。将stackpane视为一个节点堆栈，每个节点一个叠在另一个上面，就好像您在物理上堆叠它们一样。很确定你只需要一个stackpane与你的圆圈和三角形添加到他们代表一个8球。