アプリケーション開始メソッドの例外がヌルルートによって発生しました

Question

私のコードは私にこのエラーを与えます。

primaryStage.setScene(new Scene(vb, 400, 300));` 

「ルートはNULLにすることはできません」というエラー：今すぐスタックはエラーをトレース読んで、私の限られた知識から、このコード行によって原因があります。ルートがvbであると、私はそれを初期化したと考えて、どのようにnullになるのか理解していません。どんな助けでも大歓迎です。

import javafx.application.Application; 
    import javafx.beans.value.ChangeListener; 
    import javafx.beans.value.ObservableValue; 
    import javafx.scene.Scene; 
    import javafx.scene.control.Button; 
    import javafx.scene.control.ComboBox; 
    import javafx.scene.control.Label; 
    import javafx.scene.control.ProgressBar; 
    import javafx.scene.control.RadioButton; 
    import javafx.scene.control.Slider; 
    import javafx.scene.control.TextField; 
    import javafx.scene.layout.VBox; 
    import javafx.stage.Stage; 
    import javafx.beans.value.ObservableValue; 
    import javafx.scene.control.Toggle; 
    import javafx.scene.control.ToggleGroup; 
    import javafx.scene.layout.GridPane; 
    import javafx.scene.layout.HBox; 
    import javafx.event.ActionEvent; 
    import javafx.event.EventHandler; 
    import java.text.DecimalFormat; 
// class definition 
public class Projectile extends Application { 

// init method 
public void init() { 

    // Projectile Type - ComboBox 
    VBox vb = new VBox(); 
    projectile_type_combobox = new ComboBox<String>(); 
    projectile_type_label = new Label("Projectile Type"); 
    projectile_type_combobox.getItems().addAll("Human", "Piano"); 

    // Inital Speed ToggleGroup 
    initial_speed_toggleGroup = new ToggleGroup(); 
    label_display = new Label("Radio Button 1 selected"); 
    initial_speed_slow = new RadioButton("Slow"); 
    initial_speed_medium = new RadioButton("Medium"); 
    initial_speed_fast = new RadioButton("Fast"); 

    initial_speed_slow.setToggleGroup(tg_radiobutton_group); 
    initial_speed_slow.setToggleGroup(tg_radiobutton_group); 
    initial_speed_fast.setToggleGroup(tg_radiobutton_group); 

    // use the .setUserData command of the radio button to store speeds 
    initial_speed_slow.setUserData("10"); 
    initial_speed_medium.setUserData("50"); 
    initial_speed_fast.setUserData("70"); 

    // Mass 
    mass_textField = new TextField(); 
    mass_label = new Label("Mass(kgs)"); 

    // Angle 
    angle_textField = new TextField(); 
    angle_label = new Label("Angle(Degrees)"); 

    // Speed 
    intitial_speed_textField = new TextField(); 
    initial_speed_label = new Label("Initial Speed"); 

    // Range 
    range_textField = new TextField(); 
    range_label = new Label(); 

    // Height 
    height_textField = new TextField(); 
    height_label = new Label(); 

    // Time 
    time_label = new Label(); 
    time_textField = new TextField(); 

    // Button 
    fire_button = new Button("Fire"); 
    erase_button = new Button("Erase"); 

    // Prevent the following TextFields from being editable: angle,intial 
    // speed range, height, time 
    // setEditable(false); 

    // Layout controls as per the diagram, feel free to improve the UI. 
    // How many rows and columns do you want - work this out on paper first 
    // My version has 7 rows, you can look at the JavaFX API to see how to 
    // get controls to span more than one column 

    gp = new GridPane(); 
    gp.addRow(0, projectile_type_label, projectile_type_combobox); 
    gp.addRow(1, mass_textField, mass_label); 
    gp.addRow(2, angle_label, angle_textField); 
    gp.addRow(3, initial_speed_label, intitial_speed_textField); 
    gp.addRow(4, range_label, range_textField); 
    gp.addRow(5, height_label, height_textField); 
    gp.addRow(6, time_label, time_textField); 
    gp.addRow(7, fire_button, erase_button); 

    // Method call (not declaration!) to initialize the controls based on 
    // the projectile type. 
    initalizeControlValues(); 



// Listener for angle Slider to set angle TextTield and the angle 
     // variable 
     angle_slider.valueProperty().addListener(new ChangeListener<Number>() { 
      public void changed(final ObservableValue<? extends Number> observable, final Number oldValue, 
        final Number newValue) { 
       angle = (double) newValue; 
       angle_textField.setText("" + newValue); 

      } 

    }); 

    // Listener for inital_speed ToggleGroup to set initital_speed TextField 
    this.initial_speed_toggleGroup.selectedToggleProperty().addListener(new ChangeListener<Toggle>() { 
     public void changed(ObservableValue<? extends Toggle> ov, Toggle toggle, Toggle new_toggle) { 

      intitial_speed_textField.setText("" + new_toggle); 

     } 
    }); 

    vb.getChildren().addAll(projectile_type_combobox, projectile_type_label, label_display, initial_speed_slow, 
      initial_speed_medium, initial_speed_fast, mass_textField, mass_label, angle_textField, angle_label, 
      intitial_speed_textField, initial_speed_label, range_textField, range_label, height_textField, 
      height_label, time_label, gp, time_textField, fire_button, erase_button); 





    // Listener to call the fire() method when the fire button is pressed 

    fire_button.setOnAction(new EventHandler<ActionEvent>() { 

     @Override 
     public void handle(ActionEvent event) { 
      fire(); 
     } 
    }); 

    // Listener to initialize control values if the projectile type is 
    // changed 

    // Listener to initialize control values if the erase button is pressed 
    // erase_button.setOnAction(new EventHandler<ActionEvent>() { 

    // @Override 
    // public void handle(ActionEvent event) { 
    // erase(); 
    // } 
    // }); 
} 

// Overridden start method 
@Override 
public void start(Stage primaryStage) { 

    primaryStage.setTitle("Projectile"); 

    primaryStage.setScene(new Scene(vb, 400, 300)); 
    primaryStage.show(); 

} 

// Overridden stop method add functionality to this if you wish. 
public void stop() { 

} 

// Entry point to our program 
public static void main(String[] args) { 
    launch(args); 

} 

// Method to harvest values from controls, perform calculation and display 
// the results 
private void fire() { 
    // capture the values from the text fields outputting number errors 
    // where relevant 

    // don't forget to convert your angle input to radians for use with 
    // Math.sin() 

    // calculate the range of the projectile 
    range = ((initial_speed * initial_speed)/gravitational_accelleration) * Math.sin(2 * angle); 

    // calculate the flight time of the projectile 
    time = ((2 * initial_speed) * Math.sin(angle))/gravitational_accelleration; 

    // calculate the max height of the projectile 
    height = ((initial_speed * initial_speed) * Math.sin(angle))/2 * gravitational_accelleration; 

    // display the results in the relevant TextFields 

} 

private void erase() { 

    if (projectile_type_combobox.getValue() == "Human") { 

     mass = 80; 

     // Set slider scale 0 to 90, set slider value to 45 and ticks to 
     // units 
     angle_slider = new Slider(0, 45, 90); 
     angle_slider.setShowTickMarks(true); 
     angle_slider.setShowTickLabels(true); 
     angle_slider.setMajorTickUnit(15); 
     angle_slider.setBlockIncrement(0.5); 

     // initalize the intital speed to fast 

     this.initial_speed_fast.setSelected(true); 
     this.intitial_speed_textField.setText((String) this.initial_speed_fast.getUserData()); 

    } 

    else { 
     // inital the mass to 400kg 
     mass = 400; 

     // Set slider scale 0 to 40, set slider value to 20 and ticks to 10 
     // units 
     angle_slider = new Slider(0, 20, 40); 
     angle_slider.setShowTickMarks(true); 
     angle_slider.setShowTickLabels(true); 
     angle_slider.setMajorTickUnit(10); 
     angle_slider.setBlockIncrement(0.5); 
     // initalize the intial speed to slow 
     this.initial_speed_slow.setSelected(true); 
     this.intitial_speed_textField.setText((String) this.initial_speed_slow.getUserData()); 
    } 

} 

// Method to initalize the controls based on the selection of the projectile 
// type 
private void initalizeControlValues() { 
    if (projectile_type_combobox.getValue() == "Human") { 

     mass = 80; 

     // Set slider scale 0 to 90, set slider value to 45 and ticks to 
     // units 
     angle_slider = new Slider(0, 45, 90); 
     angle_slider.setShowTickMarks(true); 
     angle_slider.setShowTickLabels(true); 
     angle_slider.setMajorTickUnit(15); 
     angle_slider.setBlockIncrement(0.5); 

     // initalize the intital speed to fast 

     this.initial_speed_fast.setSelected(true); 
     this.intitial_speed_textField.setText((String) this.initial_speed_fast.getUserData()); 

    } 

    else { 
     // inital the mass to 400kg 
     mass = 400; 

     // Set slider scale 0 to 40, set slider value to 20 and ticks to 10 
     // units 
     angle_slider = new Slider(0, 20, 40); 
     angle_slider.setShowTickMarks(true); 
     angle_slider.setShowTickLabels(true); 
     angle_slider.setMajorTickUnit(10); 
     angle_slider.setBlockIncrement(0.5); 
     // initalize the intial speed to slow 
     this.initial_speed_slow.setSelected(true); 
     this.intitial_speed_textField.setText((String) this.initial_speed_slow.getUserData()); 
    } 
    // display ticks etc 

    // clear the results fields and variables 

    // The following variables SHOULD be initialized where appropriate as 
    // declaring and 
    // initializing separately is very verbose. 

} 

// Textfield 

// Slider 
private Label sli_display; 
private Slider sli_slider; 

// Radio Buttons 
private RadioButton rb1, rb2, rb3; 
private ToggleGroup tg_radiobutton_group; 
private Label label_display; 

private VBox vb; 

// Layout 
private GridPane gp; 

// Projectile Type 
private Label projectile_type_label; 
private ComboBox<String> projectile_type_combobox; 

// Mass 
private Label mass_label; 
private TextField mass_textField; 
private double mass; 

// Angle 
private Label angle_label; 
private Slider angle_slider; 
private TextField angle_textField; 
private double angle; 
// Formating the values in the duration box 
DecimalFormat df; 

// Initial Speed 
private Label initial_speed_label; 
private ToggleGroup initial_speed_toggleGroup; 
private RadioButton initial_speed_slow; 
private RadioButton initial_speed_medium; 
private RadioButton initial_speed_fast; 
private TextField intitial_speed_textField; 
private double initial_speed; 

// Range 
private Label range_label; 
private TextField range_textField; 
private double range; 

// Height 
private Label height_label; 
private TextField height_textField; 
private double height; 

// Time 
private Label time_label; 
private TextField time_textField; 
private double time; 

// Gravity 
private static final double gravitational_accelleration = 9.81; // m/s/s 

// Calculate 
private Button fire_button; 
private Button erase_button; 
} 



Exception in Application start method 
java.lang.reflect.InvocationTargetException 
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) 
    at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source) 
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source) 
    at java.lang.reflect.Method.invoke(Unknown Source) 
    at com.sun.javafx.application.LauncherImpl.launchApplicationWithArgs(LauncherImpl.java:389) 
    at com.sun.javafx.application.LauncherImpl.launchApplication(LauncherImpl.java:328) 
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) 
    at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source) 
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source) 
    at java.lang.reflect.Method.invoke(Unknown Source) 
    at sun.launcher.LauncherHelper$FXHelper.main(Unknown Source) 
Caused by: java.lang.RuntimeException: Exception in Application start method 
    at com.sun.javafx.application.LauncherImpl.launchApplication1(LauncherImpl.java:917) 
    at com.sun.javafx.application.LauncherImpl.lambda$launchApplication$155(LauncherImpl.java:182) 
    at java.lang.Thread.run(Unknown Source) 
Caused by: java.lang.NullPointerException: Root cannot be null 
    at javafx.scene.Scene.<init>(Scene.java:336) 
    at javafx.scene.Scene.<init>(Scene.java:223) 
    at Projectile.start(Projectile.java:171) 
    at com.sun.javafx.application.LauncherImpl.lambda$launchApplication1$162(LauncherImpl.java:863) 
    at com.sun.javafx.application.PlatformImpl.lambda$runAndWait$175(PlatformImpl.java:326) 
    at com.sun.javafx.application.PlatformImpl.lambda$null$173(PlatformImpl.java:295) 
    at java.security.AccessController.doPrivileged(Native Method) 
    at com.sun.javafx.application.PlatformImpl.lambda$runLater$174(PlatformImpl.java:294) 
    at com.sun.glass.ui.InvokeLaterDispatcher$Future.run(InvokeLaterDispatcher.java:95) 
    at com.sun.glass.ui.win.WinApplication._runLoop(Native Method) 
    at com.sun.glass.ui.win.WinApplication.lambda$null$148(WinApplication.java:191) 
    ... 1 more 
Exception running application Projectile 

Answer 1

あなたがvbと呼ばれるフィールドを初期化しませんでした：あなたはinit()メソッド内のローカル変数を宣言した（も）vbと呼ばれ、これを初期化。

vb = new VBox(); 

と

VBox vb = new VBox(); 

を交換してください