线程“ main”中的异常java.lang.RuntimeException：无法构造应用程序实例：类View

Question

I am trying to instantiate an object of type Application outside of where I wrote my static main method and I am getting this exception.

public class Main {
    public static void main(String[] args) {
        new View(args);
    }
}

---

import javafx.application.Application;

public class View extends Application {
    public View(String... args) {
        launch(args);
    }

    @Override
    public void start(Stage primaryStage) throws Exception {
    }
}

The stack trace:

Exception in Application constructor
Exception in thread "main" java.lang.RuntimeException: Unable to construct Application instance: class View
    at com.sun.javafx.application.LauncherImpl.launchApplication1(LauncherImpl.java:907)
    at com.sun.javafx.application.LauncherImpl.lambda$launchApplication$152(LauncherImpl.java:182)
    at com.sun.javafx.application.LauncherImpl$$Lambda$2/1867083167.run(Unknown Source)
    at java.lang.Thread.run(Thread.java:745)
Caused by: java.lang.reflect.InvocationTargetException
    at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
    at sun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:62)
    at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:45)
    at java.lang.reflect.Constructor.newInstance(Constructor.java:422)
    at com.sun.javafx.application.LauncherImpl.lambda$launchApplication1$158(LauncherImpl.java:819)
    at com.sun.javafx.application.LauncherImpl$$Lambda$46/1861073381.run(Unknown Source)
    at com.sun.javafx.application.PlatformImpl.lambda$runAndWait$172(PlatformImpl.java:326)
    at com.sun.javafx.application.PlatformImpl$$Lambda$48/1540794519.run(Unknown Source)
    at com.sun.javafx.application.PlatformImpl.lambda$null$170(PlatformImpl.java:295)
    at com.sun.javafx.application.PlatformImpl$$Lambda$50/1604144171.run(Unknown Source)
    at java.security.AccessController.doPrivileged(Native Method)
    at com.sun.javafx.application.PlatformImpl.lambda$runLater$171(PlatformImpl.java:294)
    at com.sun.javafx.application.PlatformImpl$$Lambda$49/718368050.run(Unknown Source)
    at com.sun.glass.ui.InvokeLaterDispatcher$Future.run(InvokeLaterDispatcher.java:95)
    at com.sun.glass.ui.win.WinApplication._runLoop(Native Method)
    at com.sun.glass.ui.win.WinApplication.lambda$null$145(WinApplication.java:101)
    at com.sun.glass.ui.win.WinApplication$$Lambda$38/1823101961.run(Unknown Source)
    ... 1 more
Caused by: java.lang.IllegalStateException: Application launch must not be called more than once
    at com.sun.javafx.application.LauncherImpl.launchApplication(LauncherImpl.java:162)
    at com.sun.javafx.application.LauncherImpl.launchApplication(LauncherImpl.java:143)
    at javafx.application.Application.launch(Application.java:252)
    at View.<init>(View.java:33)
    ... 18 more

Answer 1

Not sure what are you trying to do, but invoking launch(args) in your constructor looks wrong. From javadocs ( https://docs.oracle.com/javase/8/javafx/api/javafx/application/Application.html#launch-java.lang.String...- ):

The launch method does not return until the application has exited, either via a call to Platform.exit or all of the application windows have been closed.

Even if it worked, it would hang in your constructor. If you need to do it outside main() method, use some static instantiator.