code: public void doNew(String[] dropdownMimeTypes, boolean makeSelected) {
          int i = getTabIndex("New...");
  
          m_tabbedPane
                  .setComponentAt(i, new NewDatastreamPane(dropdownMimeTypes));
          i = getTabIndex("New...");
          m_tabbedPane.setToolTipTextAt(i, "Add a new datastream to this object");
          m_tabbedPane.setIconAt(i, newIcon);
          m_tabbedPane.setBackgroundAt(i, Administrator.DEFAULT_COLOR);
          if (makeSelected) {
              m_tabbedPane.setSelectedIndex(i);
          }
      }
docs: Set the content of the "New..." JPanel to a fresh new datastream entry
  panel, and switch to it, if needed.