Hello with JavaFX

Here is the HelloWorld JavaFX application that shows the text, Hello, World! and Exit:

import javafx.application.Application;
import javafx.application.Platform;
import javafx.scene.control.Button;
import javafx.scene.layout.Pane;
import javafx.scene.text.Text;
import javafx.scene.Scene;
import javafx.stage.Stage;

public class HelloWorld extends Application {
    public static void main(String... args) {
        launch(args);
    }
    @Override
    public void start(Stage primaryStage) {
        Text txt = new Text("Hello, world!");
        txt.relocate(135, 40);

        Button btn = new Button("Exit");
        btn.relocate(155, 80);
        btn.setOnAction(e:> {
            System.out.println("Bye! See you later!");
            Platform.exit();
        });

        Pane pane = new Pane();
        pane.getChildren().addAll(txt, btn);

        primaryStage...