JavaFX开发文本分析工具使用HBox报构造异常如何解决

报错堆栈最底层的NullPointerException已经明确指向问题根源：你为HBox添加的子节点为null。
你在类成员初始化阶段就执行了HBox hbox = new HBox(button, button2, button3);，但此时三个Button变量仅完成声明、没有完成实例化，默认值都是null，JavaFX布局容器不允许添加null作为子节点，因此构造HBox时直接抛出异常，导致Application实例初始化失败。

第一步 调整HBox初始化逻辑 #

修改HBox的初始化方式，避免传入未实例化的按钮：
原有错误的成员变量代码：

Button button, button2, button3;
HBox hbox = new HBox(button, button2, button3);

修改为：

Button button, button2, button3;
// 初始化为空HBox即可
HBox hbox = new HBox();

你原有start()方法中已经写了hbox.getChildren().addAll(button, button2, button3);，此时按钮已经完成实例化，可以正常添加到HBox中。

第二步 修复if判断语法错误 #

你代码中所有if判断后都多写了多余的分号，会导致判断逻辑完全失效：

// 错误写法：分号会直接结束if判断，后面的代码块无论条件是否满足都会执行
if (event.getSource() == button) ;
{
    // 逻辑代码
}

把每个if后面的分号删除即可：

if (event.getSource() == button)
{
    // 逻辑代码
}

否则点击任意按钮都会触发所有按钮的执行逻辑，无法实现分步操作的预期效果。

public class Text_Processor extends Application implements EventHandler<ActionEvent> {
    Button button, button2, button3;
    HBox hbox = new HBox();

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

    @Override
    public void start(Stage primaryStage) throws Exception {
        primaryStage.setTitle("Word Analyzer");

        button = new Button();
        button.setText("Click First to Fetch The Raven Text");
        button.setOnAction(this);
        button2 = new Button();
        button2.setText("Click Here Next to parse the file");
        button2.setOnAction(this);
        button3 = new Button();
        button3.setText("Click Here Last to display results");
        button3.setOnAction(this);
        hbox.getChildren().addAll(button, button2, button3);
        // 可添加间距优化布局显示
        hbox.setSpacing(10);

        Scene scene = new Scene(hbox, 600, 100);
        primaryStage.setScene(scene);
        primaryStage.show();
    }

    @Override
    public void handle(ActionEvent event) {
        if (event.getSource() == button)
        {
            System.out.println("Fetching Text From Source https://www.gutenberg.org/files/1065/1065-h/1065-h.htm");
            URL url;
            try {
                url = new URL("https://www.gutenberg.org/files/1065/1065-h/1065-h.htm");
                BufferedReader readr = new BufferedReader(new InputStreamReader(url.openStream()));
                BufferedWriter writer = new BufferedWriter(new FileWriter("Test_Download.txt"));
                String line;
                while ((line = readr.readLine()) != null)
                {
                    writer.write(line);
                }
                readr.close();
                writer.close();
            } catch
            (IOException e) {
                System.out.println("Error: " + e.getMessage());
                e.printStackTrace();
            }

        }

        if (event.getSource() == button2)
        {
            System.out.println("Parsing text of your downloaded file...");
            try {
                File input = new File("Test_Download.txt");
                Document doc = Jsoup.parse(input, "UTF-8");
                String body = doc.body().text();
                BufferedWriter writer = new BufferedWriter(new FileWriter("Test_Download.txt"));
                writer.write(body);
                writer.close();
            } catch (IOException e) {
                System.out.println("Error: " + e.getMessage());
                e.printStackTrace();
            }

        }

        if (event.getSource() == button3)
        {
            try {
                File file = new File("Test_Download.txt");
                Scanner sc = new Scanner(file);
                int i = 0, indexOfWord = 0, count = 0;
                List<String> words = new ArrayList<String>();
                List<Integer> wordCount = new ArrayList<Integer>();

                while (sc.hasNext())
                {
                    String word = sc.next();
                    word = word.replaceAll("\\p{Punct}", " ");
                    if (words.contains(word))
                    {
                        indexOfWord = words.indexOf(word);
                        count = wordCount.get(indexOfWord);
                        count = count + 1;
                        wordCount.add(indexOfWord, count);
                    } else {
                        words.add(i, word);
                        wordCount.add(i, 1);
                        i++;
                    }
                }
                sc.close();


                Integer max = Collections.max(wordCount);
                System.out.println("max word occurence is:" + max);
                System.out.println("|Count|Word");
                System.out.println("|-----|-----------------|");

                int no_of_elements = words.size();

                while (max != 0) {
                    for (int j = 0; j < no_of_elements; j++) {
                        String word = words.get(j);
                        count = wordCount.get(j);
                        if (count == max) {
                            System.out.printf("|%-4d", count);
                            System.out.printf(" |" + word + "\n");
                        }

                    }
                    max--;
                }
            } catch (IOException e) {
                System.out.println("Error: " + e.getMessage());
                e.printStackTrace();
            }

        }
    }
}

内容的提问来源于stack exchange，提问作者dheeke