"Hallo Welt" mit Fenster und Knopf

import javafx.application.*;
import javafx.scene.Scene;
import javafx.scene.control.Label;
import javafx.scene.control.Button;
import javafx.scene.layout.*;
import javafx.stage.Stage;
 
public class HelloFX extends Application {
 
    @Override
    public void start(Stage stage) {
        // Button
        Button btn = new Button();
        btn.setText("Hallo Welt!");
        btn.setOnAction( (event) -> Platform.exit() );
 
        // Stackpane "root" 
        Pane root = new StackPane();
        // Knopf anfügen
        root.getChildren().add(btn);
 
        stage.setScene(new Scene(root, 300,150) );
        stage.show();
    }
 
    public static void main(String[] args) {
        launch();
    }
 
}