GWT OkCancel Dialog

import java.util.Optional;
import java.util.function.BiConsumer;
import com.google.gwt.user.client.ui.*;
import com.google.gwt.user.client.Event;
import com.google.gwt.event.dom.client.*;

@SuppressWarnings({"OptionalUsedAsFieldOrParameterType", "WeakerAccess", "unused"})
public class OkCancelDialog<T extends Widget> extends DialogBox {
    protected final T widget;
    protected final BiConsumer<T, OkCancelDialog<T>> onClick;
    protected final Button btnOk;
    protected Optional<Focusable> onCloseFocusedWidget = Optional.empty();

    public OkCancelDialog(String title, T widget, BiConsumer<T, OkCancelDialog<T>> onClick) {
        this.widget = widget;
        this.onClick = onClick;

        final VerticalPanel mainPanel = new VerticalPanel();
        final Panel buttonsPanel = new HorizontalPanel();

        btnOk = new Button("OK", (ClickHandler) e -> onClick.accept(widget, this));

        mainPanel.setHorizontalAlignment(VerticalPanel.ALIGN_RIGHT);
        mainPanel.add(new Anchor("×", "#") {{addClickHandler(e -> hide()); setStyleName("mg-CloseButton");}});
        mainPanel.add(widget);
        mainPanel.add(new HTML("<hr/>"));
        mainPanel.add(buttonsPanel);

        buttonsPanel.setStyleName("buttons-panel");
        buttonsPanel.add(btnOk);

        setText(title);
        setWidget(mainPanel);
    }

    public OkCancelDialog withOnCloseFocusable(Focusable widget) {
        onCloseFocusedWidget = Optional.of(widget);
        return this;
    }

    public OkCancelDialog withButtonText(String text) {
        btnOk.setText(text);
        return this;
    }

    @Override
    public void show() {
        super.show();
        if (widget instanceof Focusable)
            ((Focusable) widget).setFocus(true);
    }

    @Override
    public void center() {
        super.center();
        if (widget instanceof Focusable)
            ((Focusable) widget).setFocus(true);
    }

    @Override
    public void hide() {
        super.hide();
        onCloseFocusedWidget.ifPresent(f -> f.setFocus(true));
    }

    @Override
    protected void onPreviewNativeEvent(Event.NativePreviewEvent event) {
        super.onPreviewNativeEvent(event);
        if (event.getTypeInt() == Event.ONKEYDOWN) {
            final int code = event.getNativeEvent().getKeyCode();
            switch (code) {
                case KeyCodes.KEY_ENTER: btnOk.click(); break;
                case KeyCodes.KEY_ESCAPE: hide(); break;
            }
        }
    }
}

/*
.mg-CloseButton, .mg-CloseButton:visited, .mg-CloseButton:hover {
  color: aliceblue;
  float: right;
  display: block;
  margin-top: -52px;
  font-size: 2.5rem;
  padding-right: .3rem;
  text-decoration: none;
}
*/