我正在使用javaFX 8，我想要一种在子窗体仍处于打开状态时阻止用户访问父窗体的方法

Stage primaryStage = new Stage();
primaryStage.setTitle("父窗体");

Stage childStage = new Stage();
childStage.setTitle("子窗体");

childStage.initModality(Modality.APPLICATION_MODAL);

primaryStage.show();
childStage.showAndWait();

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

public class Main extends Application {

    @Override
    public void start(Stage primaryStage) {
        primaryStage.setTitle("父窗体");

        Stage childStage = new Stage();
        childStage.setTitle("子窗体");
        childStage.initModality(Modality.APPLICATION_MODAL);

        Button closeButton = new Button("关闭子窗体");
        closeButton.setOnAction(event -> childStage.close());

        VBox layout = new VBox(10);
        layout.getChildren().addAll(closeButton);
        Scene scene = new Scene(layout, 200, 200);
        childStage.setScene(scene);

        primaryStage.show();
        childStage.showAndWait();
    }

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