@SuppressWarnings("unchecked")
    public <G> GroupingOptions<G> activateGrouping(final Function<T, G> groupMapper) {
        this.groupingOptions.setGroupMapper((Function<T, Object>) groupMapper);
        return (GroupingOptions<G>) this.groupingOptions;
    }
Activates Grouping for this model with given groupMapper. Returns a GroupingOptions instance to set further grouping settings.
main/src/main/java/cgeo/geocaching/ui/SimpleItemListModel.java