abstract sclass DynCalculatedList extends DynModule {
  transient JList list;

  JComponent visualize() { ret list = jlist(calc()); }
  void unvisualize2() { list = null; }  
  void update() {
    lock lock;
    if (list != null) fillListWithStrings(list, calc());
  }

  // should cache results if they are expensive to make
  abstract L<S> calc();
}