FocusBug

package focusbug;

import javafx.application.Application;
import javafx.event.ActionEvent;
import javafx.event.EventHandler;
import javafx.scene.Parent;
import javafx.scene.Scene;
import javafx.scene.control.Button;
import javafx.scene.control.Label;
import javafx.scene.control.TextField;
import javafx.scene.layout.HBoxBuilder;
import javafx.scene.layout.VBoxBuilder;
import javafx.stage.Stage;

public class FocusBug extends Application {
    public static void main(String[] args) {
        launch(args);
    }

    @Override
    public void start(Stage mainStage ) {
        mainStage.setScene(new Scene(getRootNode()));
        mainStage.show();
    }

    public Parent getRootNode() {
        final TextField textField = new TextField();
        textField.setId("mainTextField");

        final Button clickMeButton = new Button("Click me to show popup");
        clickMeButton.setId("clickMeButton");
        clickMeButton.setOnAction(showPopupWindow());

        return VBoxBuilder.create().children(textField, clickMeButton).build();
    }

    private EventHandler<ActionEvent> showPopupWindow() {
        return new EventHandler<ActionEvent>() {

            @Override
            public void handle(ActionEvent actionEvent) {
                final Label label = new Label("Enter text:");
                label.setId("popupLabel");

                final TextField textField = new TextField();
                textField.setId("popupTextField");

                final Stage stage = new Stage();
                stage.setTitle("Popup");
                stage.setScene(new Scene(HBoxBuilder.create().children(label, textField).build()));
                stage.show();
            }
        };
    }
}