public void setSortOrder(int sortOrder) {
        if (!(sortOrder == PubsubNodeResultFilter.ASCENDING || sortOrder == PubsubNodeResultFilter.DESCENDING)) {
            throw new IllegalArgumentException();
        }
        this.sortOrder = sortOrder;
    }
Sets the sort order. Valid arguments are {@link #ASCENDING} for ascending sorting, and {@link #DESCENDING} for
descending sorting.

Descending sorting is: 3, 2, 1, etc. Ascending sorting is 1, 2, 3, etc.

@param sortOrder the order that results will be sorted in.
xmppserver/src/main/java/org/jivesoftware/openfire/pubsub/PubsubNodeResultFilter.java