public GroupingOptions<G> setItemGroupComparator(final Comparator<Object> groupComparator) {
            this.itemGroupComparator = groupComparator;
            triggerChange(ChangeType.COMPLETE);
            return this;
        }
Sets a comparator specifying how groups and items are sorted. Comparator must be able to handle lists of items of T and G intermixed
main/src/main/java/cgeo/geocaching/ui/SimpleItemListModel.java