public long getStates(final String topicName) {
    return topicNameToEventCount.getOrDefault(topicName, 0L);
  }
Returns the number of events received for a specific topic.

@param topicName the name of the topic
@return the number of events received for the topic
iotdb-core/datanode/src/main/java/org/apache/iotdb/db/subscription/broker/SubscriptionStates.java