How to start JavaFX app on Java 8 Ubuntu today?

Question

Im trying to start application but got errors:

java.lang.ClassNotFoundException: com.sun.glass.ui.gtk.GtkPlatformFactory   at
  java.net.URLClassLoader.findClass(URLClassLoader.java:381)  at
  java.lang.ClassLoader.loadClass(ClassLoader.java:424)   at
  java.lang.ClassLoader.loadClass(ClassLoader.java:357)   at
  java.lang.Class.forName0(Native Method)   at
  java.lang.Class.forName(Class.java:264)   at
  com.sun.glass.ui.PlatformFactory.getPlatformFactory(PlatformFactory.java:42)
    at com.sun.glass.ui.Application.run(Application.java:146)   at
  com.sun.javafx.tk.quantum.QuantumToolkit.startup(QuantumToolkit.java:257)
    at
  com.sun.javafx.application.PlatformImpl.startup(PlatformImpl.java:211)
    at
  com.sun.javafx.application.LauncherImpl.startToolkit(LauncherImpl.java:675)
    at
  com.sun.javafx.application.LauncherImpl.launchApplicationWithArgs(LauncherImpl.java:337)
    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$FXHelper.main(LauncherHelper.java:767)
  Exception in thread "main" java.lang.reflect.InvocationTargetException
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)  at
  sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
    at
  sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:498)   at
  sun.launcher.LauncherHelper$FXHelper.main(LauncherHelper.java:767)
  Caused by: java.lang.NullPointerException   at
  com.sun.glass.ui.Application.run(Application.java:146)  at
  com.sun.javafx.tk.quantum.QuantumToolkit.startup(QuantumToolkit.java:257)
    at
  com.sun.javafx.application.PlatformImpl.startup(PlatformImpl.java:211)
    at
  com.sun.javafx.application.LauncherImpl.startToolkit(LauncherImpl.java:675)
    at
  com.sun.javafx.application.LauncherImpl.launchApplicationWithArgs(LauncherImpl.java:337)
    at
  com.sun.javafx.application.LauncherImpl.launchApplication(LauncherImpl.java:328)
    ... 5 more 

And a message Failed to load Glass factory class at the end of the stack trace.

I also tried to add javafx as a maven dependency and to add this jar to classpath. And I use IDEA for my project.

UPDATE :

My code is simple Hello JavaFX exmaple:

public class Application extends javafx.application.Application {

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

    @Override
    public void start(Stage primaryStage) {
        Button btn = new Button();
        btn.setText("Say 'Hello World'");
        btn.setOnAction(new EventHandler<ActionEvent>() {

            public void handle(ActionEvent event) {
                System.out.println("Hello World!");
            }
        });

        StackPane root = new StackPane();
        root.getChildren().add(btn);

        Scene scene = new Scene(root, 300, 250);

        primaryStage.setTitle("Hello World!");
        primaryStage.setScene(scene);
        primaryStage.show();
    }
}

UPDATE 1:

I used debug and found the excpetion throws inside ThreadPoolExecutor.java at line 1057. Also:

And yes! After executing this code fragment first exception appears in the project console.

Answer 1

You need to download and install the openjfx lib.

sudo apt install openjfx should do the trick.

Answer 2

Ok, I figured it out.

Firstly my jdk was broken so I downloaded new one.

And also in IDEA don't forget to change project sdk in Modules section even if you changed your sdk in Project tab.