如何只打开一次JavaFX窗口

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

public class Main extends Application {
    private boolean windowOpened = false;

    @Override
    public void start(Stage primaryStage) {
        primaryStage.setTitle("JavaFX Window");
        primaryStage.setWidth(400);
        primaryStage.setHeight(300);

        VBox root = new VBox();
        Button button = new Button("Open Window");
        button.setOnAction(event -> {
            if (!windowOpened) {
                windowOpened = true;
                Stage secondaryStage = new Stage();
                secondaryStage.setTitle("Secondary Window");
                secondaryStage.setWidth(200);
                secondaryStage.setHeight(150);
                secondaryStage.show();
            }
        });

        root.getChildren().add(button);
        Scene scene = new Scene(root);
        primaryStage.setScene(scene);
        primaryStage.show();
    }

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