@Override
    public int hashCode() {
        int result = id.hashCode();
        result = 31 * result + name.hashCode();
        result = 31 * result + numPartitions;
        result = 31 * result + partitionRacks.hashCode();
        return result;
    }
@return Every partition mapped to the set of corresponding available rack Ids of its replicas.
        An empty map is returned if rack information is unavailable for all partitions.
group-coordinator/src/main/java/org/apache/kafka/coordinator/group/modern/TopicMetadata.java