NoNameNow

class FlowInputDStream[Flow] (@transient ssc_ : StreamingContext, storageLevel: StorageLevel)
  extends ReceiverInputDStream[Flow](ssc_) with Logging{

error: No ClassTag available for Flow
[ERROR] class FlowInputDStream[Flow] (@transient ssc_ : StreamingContext, storageLevel: StorageLevel)

private

class DataFrame private[sql](
    @transient val sqlContext: SQLContext,
    @DeveloperApi @transient val queryExecution: SQLContext#QueryExecution) extends Serializable {

这个定义应该是class还是public 但后面是定义了一个private[sql]的constructor,那么参数定义val的目的又何在呢？