concept JG22Network is Swingable {
  new MainPanel mainPanel;
  new G22Network network;
  
  // margin on bottom/right
  transient int margin = 50;
  
  class MainPanel extends JPanel {
    *() { super(null); } // no layout manager
    
    public Dimension getPreferredSize() {
      Rect r = combinedChildBounds(this);
      print("JG22Network.getPreferredSize = " + r);
      ret new Dimension(r.x2()+margin, r.y2()+margin);
    }
    
    void revalidateMe() {
      print("JG22Network.revalidateMe");
      awtLater(0.5, -> {
        revalidateIncludingFullCenterContainer(this);
        repaint();
      });
    }
  }

  *(G22Network *network) {
    for (element : network.elements)
      visualizeElement(element);
  }
  
  void visualizeElement(G22NetworkElement element) swing {
    mainPanel.add(new JG22NetworkElement(this, element).visualize());
    mainPanel.revalidateMe();
  }
  
  void newElement {
    new G22NetworkElement element;
    element.network(network);
    network.elements.add(element);
    network.change();
    visualizeElement(element);
  }
  
  cachedVisual
    withRightAlignedButtons(jscroll_center_borderless(mainPanel),
      "New element", rThread newElement);
}