class MetadataCache {

    Cluster cluster() {
        if (clusterInstance == null) {
            throw new IllegalStateException("Cached Cluster instance should not be null, but was.");
        } else {
            return clusterInstance;
        }
    }

      MetadataCache(String clusterId,
                  Map<Integer, Node> nodes,
                  Collection<PartitionMetadata> partitions,
                  Set<String> unauthorizedTopics,
                  Set<String> invalidTopics,
                  Set<String> internalTopics,
                  Node controller);
    private  MetadataCache(String clusterId,
                          Map<Integer, Node> nodes,
                          Collection<PartitionMetadata> partitions,
                          Set<String> unauthorizedTopics,
                          Set<String> invalidTopics,
                          Set<String> internalTopics,
                          Node controller,
                          Cluster clusterInstance);

}