This class enables one to store an entry in the defaults table that's constructed each time it's looked up with one of the getXXX(key) methods. Here's an example of an ActiveValue that constructs a DefaultListCellRenderer:

  Object cellRendererActiveValue = new UIDefaults.ActiveValue() {
      public Object createValue(UIDefaults table) {
          return new DefaultListCellRenderer();
      }
  };

  uiDefaultsTable.put("MyRenderer", cellRendererActiveValue);