// x = names and components interleaving.
// or just components.
// or just names.
// also, first element can be index of tab to open at start
// also, SUPER short demo syntax: jtabs(3)
// also, you can pass a Collection containing the elements
static JTabbedPane fillJTabs(final JTabbedPane tabs, fO... _x) {
  if (tabs == null) null;
  clearTabs(tabs);
  O[] x = flattenArray2(_x);
  ifdef fillJTabs_debug
  print("fillJTabs length=" + l(_x) + " => " + l(x));
  endifdef
  int idx = 0;
  if (get(x, 0) instanceof Int) {
    idx = asInt(get(x, 0));
    x = dropFirst(x);
    if (empty(x)) {
      x = arrayrep(null, idx);
      idx = 0;
    }
  }
  int n = 0;
  for (int i = 0; i < l(x); i++) {
    ++n;
    
    // is it a component?
    O o = x[i];
    if (isComponentOrSwingable(o))
      addTab(tabs, "Tab " + n, wrap(o));
    else {
      // assume it's a tab name, optionally followed by a component
      S toolTip = "";
      
      // WithToolTip<S> is ok (WithToolTip<Component> not yet supported)
      if (o cast WithToolTip) {
        toolTip = o.toolTip();
        o = o!;
      }
      S name = str(or(o, "Tab " + n));
      ifdef fillJTabs_debug
      print("tab " + i + ": " + name);
      endifdef
      Component c;
      if (isComponentOrSwingable(get(x, i+1)))
        c = wrap(get(x, ++i));
      else
        c = new JPanel;
      addTabWithToolTip(tabs, name, toolTip, wrap(c));
    }
  }
  if (idx != 0)
    tabs.setSelectedIndex(min(tabs.getTabCount()-1, idx));
  ret tabs;
}