public Map<String, Integer> computeSubscribedTopicNames(
        ModernGroupMember oldMember,
        ModernGroupMember newMember
    ) {
        Map<String, Integer> subscribedTopicNames = new HashMap<>(this.subscribedTopicNames);
        maybeUpdateSubscribedTopicNames(
            subscribedTopicNames,
            oldMember,
            newMember
        );
        return subscribedTopicNames;
    }
Updates the subscription count.

@param oldMember             The old member.
@param newMember             The new member.

@return Copy of the map of topics to the count of number of subscribers.
group-coordinator/src/main/java/org/apache/kafka/coordinator/group/modern/ModernGroup.java