public int groupIndexOf(final int group, final Predicate<T> test) {
        final int start = groupStart(group);
        final int size = groupSize(group);
        if (start < 0 || size <= 0) {
            return -1;
        }
        for (int idx = start; idx < start + size; idx++) {
            final T candidate = get(idx);
            if (test.test(candidate)) {
                return idx;
            }
        }
        return -1;
    }
returns the list index for the first object found in given group and fulfilling given test, or -1 if there's no such object
main/src/main/java/cgeo/geocaching/utils/GroupedList.java