如何修复此“应用程序启动方法中的异常”？

Question

我是JavaFX的新手，我试图使用Netbeans IDE创建一个JavaFX FXML应用程序项目，但我遇到了这个例外。

这是我的java类：

    public class JavaFXApplication9 extends Application {

        @Override
        public void start(Stage stage) throws Exception {
            Parent root = FXMLLoader.load(getClass().getResource("FXMLDocument.fxml"));

            Scene scene = new Scene(root);

            stage.setScene(scene);
            stage.show();
        }

        /**
         * @param args the command line arguments
         */
        public static void main(String[] args) {
            launch(args);
        }

    }

这是我的FXML代码：

    <?xml version="1.0" encoding="UTF-8"?>

    <?import javafx.scene.control.Button?>
    <?import javafx.scene.layout.AnchorPane?>

    <AnchorPane id="AnchorPane" prefHeight="200" prefWidth="320" xmlns:fx="http://javafx.com/fxml/1" xmlns="http://javafx.com/javafx/8.0.171" fx:controller="javafxapplication9.FXMLDocumentController">
        <children>
            <Button fx:id="button" layoutX="126" layoutY="90" onAction="#handleButtonAction" text="Click Me!" />
        </children>
    </AnchorPane>

这是我的控制器类：

    public class FXMLDocumentController implements Initializable {

        @FXML
        private Label label;

        @FXML
        private void handleButtonAction(ActionEvent event) {
            System.out.println("You clicked me!");
            label.setText("Hello World!");
        }

        @Override
        public void initialize(URL url, ResourceBundle rb) {
            // TODO
        }    

    }

这是应用程序启动方法java.lang.reflect.InvocationTargetException javafx中异常

java.lang.reflect.InvocationTargetException
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:498)
    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(NativeMethodAccessorImpl.java:62)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:498)
    at sun.launcher.LauncherHelper$FXHelper.main(LauncherHelper.java:767)
    Caused by: java.lang.RuntimeException: Exception in Application start method
    at com.sun.javafx.application.LauncherImpl.launchApplication1(LauncherImpl.java:917)
    at com.sun.javafx.application.LauncherImpl.lambda$launchApplication$155(LauncherImpl.java:182)
    at java.lang.Thread.run(Thread.java:745)
    Caused by: java.lang.NullPointerException: Location is required.
    at javafx.fxml.FXMLLoader.loadImpl(FXMLLoader.java:3207)
    at javafx.fxml.FXMLLoader.loadImpl(FXMLLoader.java:3175)
    at javafx.fxml.FXMLLoader.loadImpl(FXMLLoader.java:3148)
    at javafx.fxml.FXMLLoader.loadImpl(FXMLLoader.java:3124)
    at javafx.fxml.FXMLLoader.loadImpl(FXMLLoader.java:3104)
    at javafx.fxml.FXMLLoader.load(FXMLLoader.java:3097)
    at javafxapplication9.JavaFXApplication9.start(JavaFXApplication9.java:22)
    at com.sun.javafx.application.LauncherImpl.lambda$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 javafxapplication9.JavaFXApplication9
    E:\Netbeans Project\JavaFXApplication9\nbproject\build-impl.xml:1052: The following error occurred 
    while executing this line:
    E:\Netbeans Project\JavaFXApplication9\nbproject\build-impl.xml:806: Java returned: 1
    BUILD FAILED (total time: 1 second)

Answer 1

此异常的主要原因是堆栈跟踪(参见NullPointerException：Location is required )。所以你尝试使用一些没有被初始化的东西。如果没有任何代码片段，很难找到错误。