Несколько модальных окон

Как то так:

    import javafx.application.Application;
    import javafx.collections.FXCollections;
    import javafx.collections.ObservableList;
    import javafx.scene.Scene;
    import javafx.scene.control.ComboBox;
    import javafx.scene.layout.HBox;
    import javafx.stage.Modality;
    import javafx.stage.Stage;
    public class ModalTest extends Application {
        @Override
        public void start(Stage primaryStage) throws Exception {
            ObservableList<String> options =
                    FXCollections.observableArrayList(
                            "Option 1",
                            "Option 2",
                            "Option 3"
                    );
            Stage dialog = new Stage();
            dialog.setWidth(100);
            dialog.setHeight(100);
            dialog.initOwner(primaryStage);
            dialog.initModality(Modality.APPLICATION_MODAL);
            ComboBox comboBox = new ComboBox(options);
            comboBox.setOnAction(event -> dialog.showAndWait());
            HBox box = new HBox(comboBox);
            primaryStage.setScene(new Scene(box));
            primaryStage.setWidth(400);
            primaryStage.setHeight(300);
            primaryStage.show();
        }
    }