code: public void openWindow(final String title, final int width, final int height, final IsWidget content) {
          closeWindow();
          window = new DefaultWindow(title);
          window.setWidth(480);
          window.setHeight(360);
          window.trapWidget(content.asWidget());
          window.setGlassEnabled(true);
          window.center();
      }
docs: ------------------------------------------------------ window management