如何在JavaFX中打开新窗口时执行代码？

import javafx.application.Application;
import javafx.event.EventHandler;
import javafx.scene.Scene;
import javafx.scene.control.Button;
import javafx.scene.layout.VBox;
import javafx.stage.Stage;
import javafx.stage.WindowEvent;

public class Main extends Application {

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

    @Override
    public void start(Stage primaryStage) {
        Button openButton = new Button("Open New Window");
        openButton.setOnAction(event -> {
            openNewWindow();
        });

        VBox root = new VBox(openButton);
        Scene scene = new Scene(root, 300, 200);

        primaryStage.setScene(scene);
        primaryStage.show();
    }

    private void openNewWindow() {
        Stage newStage = new Stage();
        Button closeButton = new Button("Close");
        closeButton.setOnAction(event -> {
            newStage.close();
        });

        VBox root = new VBox(closeButton);
        Scene scene = new Scene(root, 200, 100);

        newStage.setScene(scene);
        newStage.show();

        // 在新窗口打开时执行的代码
        System.out.println("执行新窗口打开时的代码");
    }
}