在调用方返回数据之前，如何等待JavaFX服务完成？

import javafx.application.Application;
import javafx.concurrent.Service;
import javafx.concurrent.Task;
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 WaitForService extends Application {

    @Override
    public void start(Stage primaryStage) {
        Label statusLabel = new Label("Service not started");
        Button startButton = new Button("Start Service");

        Service<String> backgroundService = new Service<String>() {
            @Override
            protected Task<String> createTask() {
                return new Task<String>() {
                    @Override
                    protected String call() throws Exception {
                        // Simulate a long-running task
                        Thread.sleep(5000);
                        return "Service completed";
                    }
                };
            }
        };

        backgroundService.setOnSucceeded(event -> {
            statusLabel.setText(backgroundService.getValue());
        });

        startButton.setOnAction(event -> {
            statusLabel.setText("Service started...");
            backgroundService.start();
        });

        VBox root = new VBox(startButton, statusLabel);
        Scene scene = new Scene(root, 300, 250);

        primaryStage.setTitle("Wait for Service");
        primaryStage.setScene(scene);
        primaryStage.show();
    }

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