import javafx.application.Application;
import javafx.beans.Observable;
import javafx.event.ActionEvent;
import javafx.stage.Stage;
import javafx.stage.StageStyle;
import javafx.scene.Scene;
import javafx.scene.control.Button;
import javafx.scene.layout.BorderPane;


public class StageClose extends Application {
    @Override public void start(Stage primaryStage) {
        try {
            BorderPane root = new BorderPane();
            Button b = new Button("Open");
            b.setOnAction((e) -> open(primaryStage));
            root.setCenter(b);
            Scene scene = new Scene(root,400,400);
            primaryStage.setScene(scene);
            primaryStage.setTitle("primary stage");
            primaryStage.show();
        } catch(Exception e) {
            e.printStackTrace();
        }
    }

    private void open(Stage primaryStage) {
        Stage utility = new Stage(StageStyle.UNDECORATED);
        BorderPane p = new BorderPane(new Button("Hello Util"));
        utility.setScene(new Scene(p,300,200));
        utility.show();
        utility.requestFocus();
        utility.focusedProperty().addListener(o -> {
            if(!utility.isFocused()) {
                System.err.println("utility.close");
                utility.close();
            }
        });
    }

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