code: @Override
      public void setJustified(final boolean justified) {
          if (justified) {
              addStyleName(Styles.BTN_GROUP_JUSTIFIED);
          } else {
              removeStyleName(Styles.BTN_GROUP_JUSTIFIED);
          }
      }
docs: Make a group of buttons stretch at the same size to span the entire width of its parent.
  <p/>
  <strong>Note:</strong> Justified button groups only work with {@link org.gwtbootstrap3.client.ui.AnchorButton} child elements!
  
  @param justified Stretch button group