Add some comments

external/kafka/src/main/scala/org/apache/spark/streaming/kafka/KafkaUtils.scala

@@ -99,7 +99,6 @@ object KafkaUtils {
    * @param topics    Map of (topic_name -> numPartitions) to consume. Each partition is consumed
    *                  in its own thread.
    * @param storageLevel RDD storage level.
-   *
    */
   def createStream(
       jssc: JavaStreamingContext,
@@ -145,6 +144,16 @@ object KafkaUtils {
       jssc.ssc, kafkaParams.toMap, Map(topics.mapValues(_.intValue()).toSeq: _*), storageLevel)
   }
 
+  /**
+   * Create an reliable input stream that pulls messages from a Kafka Broker.
+   * @param ssc       StreamingContext object
+   * @param zkQuorum  Zookeeper quorum (hostname:port,hostname:port,..)
+   * @param groupId   The group id for this consumer
+   * @param topics    Map of (topic_name -> numPartitions) to consume. Each partition is consumed
+   *                  in its own thread
+   * @param storageLevel  Storage level to use for storing the received objects
+   *                      (default: StorageLevel.MEMORY_AND_DISK_SER_2)
+   */
   def createReliableStream(
       ssc: StreamingContext,
       zkQuorum: String,
@@ -159,6 +168,15 @@ object KafkaUtils {
       ssc, kafkaParams, topics, storageLevel)
   }
 
+  /**
+   * Create an reliable input stream that pulls messages from a Kafka Broker.
+   * @param ssc         StreamingContext object
+   * @param kafkaParams Map of kafka configuration parameters,
+   *                    see http://kafka.apache.org/08/configuration.html
+   * @param topics      Map of (topic_name -> numPartitions) to consume. Each partition is consumed
+   *                    in its own thread.
+   * @param storageLevel Storage level to use for storing the received objects
+   */
   def createReliableStream[
     K: ClassTag,
     V: ClassTag,
@@ -172,7 +190,16 @@ object KafkaUtils {
     new KafkaInputDStream[K, V, U, T](ssc, kafkaParams, topics, true, storageLevel)
   }
 
-    def createReliableStream(
+  /**
+   * Create an reliable Java input stream that pulls messages form a Kafka Broker.
+   * Storage level of the data will be the default StorageLevel.MEMORY_AND_DISK_SER_2.
+   * @param jssc      JavaStreamingContext object
+   * @param zkQuorum  Zookeeper quorum (hostname:port,hostname:port,..)
+   * @param groupId   The group id for this consumer
+   * @param topics    Map of (topic_name -> numPartitions) to consume. Each partition is consumed
+   *                  in its own thread
+   */
+  def createReliableStream(
       jssc: JavaStreamingContext,
       zkQuorum: String,
       groupId: String,
@@ -181,6 +208,15 @@ object KafkaUtils {
     createReliableStream(jssc.ssc, zkQuorum, groupId, Map(topics.mapValues(_.intValue()).toSeq: _*))
   }
 
+  /**
+   * Create an reliable Java input stream that pulls messages form a Kafka Broker.
+   * @param jssc      JavaStreamingContext object
+   * @param zkQuorum  Zookeeper quorum (hostname:port,hostname:port,..).
+   * @param groupId   The group id for this consumer.
+   * @param topics    Map of (topic_name -> numPartitions) to consume. Each partition is consumed
+   *                  in its own thread.
+   * @param storageLevel RDD storage level.
+   */
   def createReliableStream(
       jssc: JavaStreamingContext,
       zkQuorum: String,
@@ -192,6 +228,19 @@ object KafkaUtils {
       storageLevel)
   }
 
+  /**
+   * Create an reliable Java input stream that pulls messages form a Kafka Broker.
+   * @param jssc      JavaStreamingContext object
+   * @param keyTypeClass Key type of RDD
+   * @param valueTypeClass value type of RDD
+   * @param keyDecoderClass Type of kafka key decoder
+   * @param valueDecoderClass Type of kafka value decoder
+   * @param kafkaParams Map of kafka configuration parameters,
+   *                    see http://kafka.apache.org/08/configuration.html
+   * @param topics  Map of (topic_name -> numPartitions) to consume. Each partition is consumed
+   *                in its own thread
+   * @param storageLevel RDD storage level.
+   */
   def createReliableStream[K, V, U <: Decoder[_], T <: Decoder[_]](
       jssc: JavaStreamingContext,
       keyTypeClass: Class[K],