为什么“java.lang.reflect.InvocationTargetException”显示

Question

我正在使用NetBeans IDE在javafx中开发项目。每当我运行我的代码时，我都会遇到一些异常。直到昨天才有问题。例外如下：

Executing E:\Project\WelcomePage\dist\run204992192\WelcomePage.jar using platform  C:\Program Files\Java\jdk1.7.0_45\jre/bin/java 
Exception in Application constructor 
java.lang.reflect.InvocationTargetException 
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) 
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57) 
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) 
at java.lang.reflect.Method.invoke(Method.java:606) 
at com.javafx.main.Main.launchApp(Main.java:698) 
at com.javafx.main.Main.main(Main.java:871) 
Caused by: java.lang.RuntimeException: Unable to construct Application instance: class welcomepage.WelcomePage 
    at com.sun.javafx.application.LauncherImpl.launchApplication1(LauncherImpl.java:393) 
    at com.sun.javafx.application.LauncherImpl.access$000(LauncherImpl.java:47) 
    at com.sun.javafx.application.LauncherImpl$1.run(LauncherImpl.java:115) 
    at java.lang.Thread.run(Thread.java:744) 
    Caused by: java.lang.NoSuchMethodException: welcomepage.WelcomePage.<init>() 
    at java.lang.Class.getConstructor0(Class.java:2810) 
    at java.lang.Class.getConstructor(Class.java:1718) 
    at com.sun.javafx.application.LauncherImpl.launchApplication1(LauncherImpl.java:275) 
    ... 3 more 
    Java Result: 1 

我的源代码非常大，所以我排除了导入语句。我将在下面提供我的部分代码：

class WelcomePage extends Application { 
@Override 
public void start(Stage stage33) { 

    BorderPane border = new BorderPane(); 

    border.setTop(addVBox()); 
    border.setLeft(addVBox1()); 

    Scene scene = new Scene(border,700,450); 
    stage33.setScene(scene); 
    stage33.setResizable(false); 
    scene.getStylesheets().add 
    (WelcomePage.class.getResource("WelcomePage.css").toExternalForm()); 
    stage33.show(); 

} 

private VBox addVBox() { 

    VBox vbox = new VBox(); 
    vbox.setPadding(new Insets(5, 12, 5, 20)); 
    vbox.setSpacing(10); // Gap between nodes 
    //vbox.setStyle("-fx-background-color: #999999;"); 

    Image image = new Image(getClass().getResourceAsStream("logo11.png")); 
    Label lb1=new Label(" C - MARK AND ATTENDANCE CALCULATOR"); 
    lb1.setAlignment(Pos.CENTER); 
    lb1.setFont(Font.font("Calibri",FontWeight.BOLD,28)); 
    lb1.setTextFill(Color.BLACK); 
    lb1.setGraphic(new ImageView(image)); 

    vbox.getChildren().addAll(lb1); 

    return vbox; 
} 

private VBox addVBox1() 
{ 
    VBox vbox1=new VBox(); 
    vbox1.setPadding(new Insets(20, 2, 15, 20)); 
    vbox1.setSpacing(20); 

    Button btnl2=new Button("SIGN IN"); 
    btnl2.setFont(Font.font("Calibri",FontWeight.BOLD,16)); 
    btnl2.setPrefSize(300,60); 
    btnl2.setStyle(" -fx-base: #0066cc;"); 

    btnl2.setOnAction(new EventHandler<ActionEvent>() { 
    @Override 
    public void handle(ActionEvent e) { 
     signin(); 
    } 
    }); 

    Button btnl4=new Button("HELP"); 
    btnl4.setFont(Font.font("Calibri",FontWeight.BOLD,16)); 
    btnl4.setPrefSize(300,60); 
    btnl4.setStyle(" -fx-base: #0066cc;"); 

    btnl4.setOnAction(new EventHandler<ActionEvent>() { 
    @Override 
    public void handle(ActionEvent e) { 
     help(); 
    } 
    }); 

    Button btnl5=new Button("ABOUT"); 
    btnl5.setFont(Font.font("Calibri",FontWeight.BOLD,16)); 
    btnl5.setPrefSize(300,60); 
    btnl5.setStyle(" -fx-base: #0066cc;"); 

    btnl5.setOnAction(new EventHandler<ActionEvent>() { 
    @Override 
    public void handle(ActionEvent e) { 
     about(); 
    } 
    }); 

    Button btnl6=new Button("EXIT"); 
    btnl6.setFont(Font.font("Calibri",FontWeight.BOLD,16)); 
    btnl6.setPrefSize(300,60); 
    btnl6.setStyle(" -fx-base: #0066cc;"); 

    btnl6.setOnAction(new EventHandler<ActionEvent>() { 
    @Override 
    public void handle(ActionEvent e) { 
     System.exit(0); 
    } 
    }); 

    vbox1.getChildren().addAll(btnl2,btnl4,btnl5,btnl6); 

    return vbox1; 
} 
public static void main(String[] args) { 
    launch(args); 
} 
} 

Answer 1

@assylias，来自评论，是正确的。由于您尚未提供访问修饰符，因此您的班级隐式具有包可见性。 Java语言规范说

默认构造函数具有默认访问暗示没有访问修饰符。

因此，编译器给出的默认无参数构造函数具有默认访问权限。

的Class#getConstructor()方法，其com.sun.javafx.application.LauncherImpl.launchApplication1使用

返回反映指定公共 构造此Class对象所表示的类的构造器对象。

但构造函数不是public，因此getConstructor(..)方法不可见。所以你得到

NoSuchMethodException - 如果没有找到匹配的方法。

自己提供一个public构造函数或使您的类public。