code: public String getSelectedId() {
  
          Widget tab = getWidget(m_tabPanel.getSelectedIndex());
          String tabId = null;
          for (Entry<String, E> tabEntry : m_tabsById.entrySet()) {
              if (tabEntry.getValue().equals(tab)) {
                  tabId = tabEntry.getKey();
                  break;
              }
          }
          return tabId;
      }
docs: Returns the id of the selected tab.<p>
  
  @return the selected tab id