Question

我曾尝试学习Java FX，所以我使用了一些Oracle Eample Code，但是当我尝试在Netbean IDE中运行它时，它给了我一个运行时错误。这是一段代码：

    public class WebViewTestOne {
    private  Scene scene;
    @Override
    public void start(Stage stage) {
    stage.setTitle("Web View");
    scene = new Scene(new Browser(),750,500, Color.web("#666970"));
    stage.setScene(scene);
    scene.getStylesheets().add("webviewsample/BrowserToolbar.css");        
    stage.show();
     }

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

     }
                              }

这是例外。

Exception in thread "main" java.lang.RuntimeException: Error: class webviewtest.one.WebViewTestOne is not a subclass of javafx.application.Application
at javafx.application.Application.launch(Application.java:254)
at webviewtest.one.WebViewTestOne.main(WebViewTestOne.java:33)
Java Result: 1

那有什么不对？我的意思是因为这是来自官方网站的一个例子，为什么即使出现错误？（错误发生在启动时（args）

编辑：根据 rob 的答案，我添加了我从示例中遗漏的扩展程序，现在它在我尝试扩展后提供了更多例外码。下面是新代码和异常日志。

   package webviewtest.one;
    import javafx.application.Application;
    import static javafx.application.Application.launch;
    import javafx.application.Platform;
    import javafx.beans.value.ChangeListener;
    import javafx.beans.value.ObservableValue;
    import javafx.collections.ListChangeListener.Change;
    import javafx.concurrent.Worker.State;
    import javafx.event.ActionEvent;
    import javafx.event.Event;
    import javafx.event.EventHandler;
    import javafx.geometry.HPos;
    import javafx.geometry.Pos;
    import javafx.geometry.VPos;
    import javafx.scene.Node;
    import javafx.scene.Scene;
    import javafx.scene.control.Button;
    import javafx.scene.control.ComboBox;
    import javafx.scene.control.Hyperlink;
    import javafx.scene.image.Image;
    import javafx.scene.image.ImageView;
    import javafx.scene.layout.HBox;
    import javafx.scene.layout.Priority;

    import javafx.scene.layout.Region;
    import javafx.scene.paint.Color;
    import javafx.scene.web.PopupFeatures;
    import javafx.scene.web.WebEngine;
    import javafx.scene.web.WebHistory;
    import javafx.scene.web.WebHistory.Entry;
    import javafx.scene.web.WebView;
    import javafx.stage.Stage;
    import netscape.javascript.JSObject;

public class WebViewTestOne extends Application{

    private Scene scene;

    @Override
    public void start(Stage stage) {
        // create scene
        stage.setTitle("Web View");
        scene = new Scene(new Browser(), 750, 500, Color.web("#666970"));
        stage.setScene(scene);
        // apply CSS style
        scene.getStylesheets().add("webviewsample/BrowserToolbar.css");
        // show stage
        stage.show();
    }

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

    }
}
class Browser extends Region {

    private HBox toolBar;
    private static String[] imageFiles = new String[]{
        "product.png",
        "blog.png",
        "documentation.png",
        "partners.png",
        "help.png"
    };
    private static String[] captions = new String[]{
        "Products",
        "Blogs",
        "Documentation",
        "Partners",
        "Help"
    };
    private static String[] urls = new String[]{
        "http://www.oracle.com/products/index.html",
        "http://blogs.oracle.com/",
        "http://docs.oracle.com/javase/index.html",
        "http://www.oracle.com/partners/index.html",
      //  WebViewSample.class.getResource("help.html").toExternalForm()
    };
    final ImageView selectedImage = new ImageView();
    final Hyperlink[] hpls = new Hyperlink[captions.length];
    final Image[] images = new Image[imageFiles.length];
    final WebView browser = new WebView();
    final WebEngine webEngine = browser.getEngine();
    final Button showPrevDoc = new Button("Toggle Previous Docs");
    final WebView smallView = new WebView();
    final ComboBox comboBox = new ComboBox();
    private boolean needDocumentationButton = false;

    public Browser() {
        //apply the styles
        getStyleClass().add("browser");

        for (int i = 0; i < captions.length; i++) {
            // create hyperlinks
            Hyperlink hpl = hpls[i] = new Hyperlink(captions[i]);
            Image image = images[i] =
            new Image(getClass().getResourceAsStream(imageFiles[i]));
            hpl.setGraphic(new ImageView(image));
            final String url = urls[i];
            final boolean addButton = (hpl.getText().equals("Documentation"));

            // process event 
            hpl.setOnAction(new EventHandler<ActionEvent>() {
                @Override
                public void handle(ActionEvent e) {
                    needDocumentationButton = addButton;
                    webEngine.load(url);
                }
            });
        }

        comboBox.setPrefWidth(60);

        // create the toolbar
        toolBar = new HBox();
        toolBar.setAlignment(Pos.CENTER);
        toolBar.getStyleClass().add("browser-toolbar");
        toolBar.getChildren().add(comboBox);
        toolBar.getChildren().addAll(hpls);
        toolBar.getChildren().add(createSpacer());

        //set action for the button
        showPrevDoc.setOnAction(new EventHandler() {
            @Override
            public void handle(Event t) {
                webEngine.executeScript("toggleDisplay('PrevRel')");
            }           
        });

        smallView.setPrefSize(120, 80);

        //handle popup windows
        webEngine.setCreatePopupHandler((PopupFeatures config) -> {
            smallView.setFontScale(0.8);
            if (!toolBar.getChildren().contains(smallView)) {
                toolBar.getChildren().add(smallView);
            }
            return smallView.getEngine();
        });

        //process history
        final WebHistory history = webEngine.getHistory();
        history.getEntries().addListener((Change<? extends Entry> c) -> {
            c.next();
            c.getRemoved().stream().forEach((e) -> {
                comboBox.getItems().remove(e.getUrl());
            });
            c.getAddedSubList().stream().forEach((e) -> {
                comboBox.getItems().add(e.getUrl());
            });
        });

        //set the behavior for the history combobox               
        comboBox.setOnAction(new EventHandler<ActionEvent>() {
            @Override
            public void handle(ActionEvent ev) {
                int offset =
                        comboBox.getSelectionModel().getSelectedIndex()
                        - history.getCurrentIndex();
                history.go(offset);
            }
        });


        // process page loading
        webEngine.getLoadWorker().stateProperty().addListener(
            new ChangeListener<State>() {
                @Override
                public void changed(ObservableValue<? extends State> ov,
                    State oldState, State newState) {
                    toolBar.getChildren().remove(showPrevDoc);    
                    if (newState == State.SUCCEEDED) {
                            JSObject win = 
                                (JSObject) webEngine.executeScript("window");
                            win.setMember("app", new JavaApp());
                            if (needDocumentationButton) {
                                toolBar.getChildren().add(showPrevDoc);
                            }
                        }
                    }
                }
        );

        // load the home page        
        webEngine.load("http://www.oracle.com/products/index.html");

        //add components
        getChildren().add(toolBar);
        getChildren().add(browser);
    }

    // JavaScript interface object
    public class JavaApp {

        public void exit() {
            Platform.exit();
        }
    }

    private Node createSpacer() {
        Region spacer = new Region();
        HBox.setHgrow(spacer, Priority.ALWAYS);
        return spacer;
    }

    @Override
    protected void layoutChildren() {
        double w = getWidth();
        double h = getHeight();
        double tbHeight = toolBar.prefHeight(w);
        layoutInArea(browser,0,0,w,h-tbHeight,0,HPos.CENTER,VPos.CENTER);
        layoutInArea(toolBar,0,h-tbHeight,w,tbHeight,0,HPos.CENTER,VPos.CENTER);
    }

    @Override
    protected double computePrefWidth(double height) {
        return 750;
    }

    @Override
    protected double computePrefHeight(double width) {
        return 600;
    }
}

这是异常日志：

    Exception in Application start method
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:483)
at     com.sun.javafx.application.LauncherImpl.launchApplicationWithArgs(LauncherImpl.java:363)
at com.sun.javafx.application.LauncherImpl.launchApplication(LauncherImpl.java:303)
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:483)    
    at sun.launcher.LauncherHelper$FXHelper.main(LauncherHelper.java:767)
Caused by: java.lang.RuntimeException: Exception in Application start method
at com.sun.javafx.application.LauncherImpl.launchApplication1(LauncherImpl.java:875)
at     com.sun.javafx.application.LauncherImpl.lambda$launchApplication$147(LauncherImpl.java:157)
at com.sun.javafx.application.LauncherImpl$$Lambda$48/128893786.run(Unknown Source)
at java.lang.Thread.run(Thread.java:745)
Caused by: java.lang.NullPointerException: Input stream must not be null
at javafx.scene.image.Image.validateInputStream(Image.java:1099)
at javafx.scene.image.Image.<init>(Image.java:684)
at webviewtest.one.Browser.<init>(WebViewTestOne.java:104)
at webviewtest.one.WebViewTestOne.start(WebViewTestOne.java:49)
at     com.sun.javafx.application.LauncherImpl.lambda$launchApplication1$153(LauncherImpl.java:821)    
at com.sun.javafx.application.LauncherImpl$$Lambda$51/1135703189.run(Unknown Source)
at com.sun.javafx.application.PlatformImpl.lambda$runAndWait$166(PlatformImpl.java:323)
at com.sun.javafx.application.PlatformImpl$$Lambda$45/1051754451.run(Unknown Source)
at com.sun.javafx.application.PlatformImpl.lambda$null$164(PlatformImpl.java:292)
at com.sun.javafx.application.PlatformImpl$$Lambda$47/135339377.run(Unknown Source)
at java.security.AccessController.doPrivileged(Native Method)
at com.sun.javafx.application.PlatformImpl.lambda$runLater$165(PlatformImpl.java:291)
at com.sun.javafx.application.PlatformImpl$$Lambda$46/1775282465.run(Unknown Source)
at com.sun.glass.ui.InvokeLaterDispatcher$Future.run(InvokeLaterDispatcher.java:95)
at com.sun.glass.ui.win.WinApplication._runLoop(Native Method)
at com.sun.glass.ui.win.WinApplication.lambda$null$141(WinApplication.java:102)
at com.sun.glass.ui.win.WinApplication$$Lambda$37/1109371569.run(Unknown Source)
... 1 more
Exception running application webviewtest.one.WebViewTestOne
Java Result: 1

Answer 1

您必须扩展应用程序。我相信错误意味着什么。

以下是Java FX网站的一个例子：

  import javafx.application.Application;
  import javafx.scene.Group;
  import javafx.scene.Scene;
  import javafx.scene.shape.Circle;
  import javafx.stage.Stage;

 public class MyApp extends Application 
 {
     public void start(Stage stage) 
     {
        Circle circ = new Circle(40, 40, 30);
        Group root = new Group(circ);
        Scene scene = new Scene(root, 400, 300);

        stage.setTitle("My JavaFX Application");
        stage.setScene(scene);
        stage.show();
     }
 }

Java运行时异常。 Java FX

1 个答案: