sclass JExtendedTabbedPane is Swingable {
  JTabbedPane tabs;
  L<Component> components;
  SingleComponentPanel scpBesideTabs = scp();
  SingleComponentPanel scpPage = scp();
  
  *(JTabbedPane tabs) swing {
    if (tabs = null) tabs = jtabs();
    this.tabs = tabs;
    int n = tabCount(tabs);
    for i to n: {
      components.add(tabs.getComponentAt(i));
      tabs.setComponentAt(i, emptyPage());
    }
      
    onTabSelectedAndNow(tabs, idx ->
      scpPage.set(getTab(tabs, idx));
  }
  
  // Something with minimum size 0
  JComponent emptyPage() { ret horizontalStrut(0); }
  
  cachedVisual
    northAndCenter(centerAndEastWithMargin(tabs, scpBesideTabs), scpPage);
}