--module-path "path/to/javafx-sdk/lib" --add-modules javafx.controls,javafx.fxml

package chapter5;

import javafx.application.Application;
import javafx.scene.Scene;
import javafx.scene.control.Button;
import javafx.scene.control.Label;
import javafx.scene.layout.VBox;
import javafx.stage.Stage;

public class FxDemo extends Application {
    public void start(Stage primaryStage) {
        Label label = new Label("Hello");
        Button button = new Button("Click Me");
        button.setOnAction(e -> label.setText("Hola"));

        VBox layout = new VBox(); // box layout - vertical, horizontal
        layout.getChildren().addAll(label, button);

        Scene scene = new Scene(layout, 300, 200);
        primaryStage.setScene(scene);
        primaryStage.setTitle("JavaFX Demo");
        primaryStage.show();
    }

    public static void main(String[] args) {
        launch(args); // auto call start()
    }
}