more comments

Author: cloud-fan

sql/core/src/main/java/org/apache/spark/sql/sources/v2/DataSourceV2.java

@@ -18,7 +18,8 @@
 package org.apache.spark.sql.sources.v2;
 
 /**
- * The base interface for data source v2 implementations.
+ * The base interface for data source v2. Implementations must have a public, no arguments
+ * constructor.
  *
  * Note that this is an empty interface, data source implementations should mix-in at least one of
  * the plug-in interfaces like `ReadSupport`. Otherwise it's just a dummy data source which is

sql/core/src/main/java/org/apache/spark/sql/sources/v2/reader/Statistics.java

@@ -20,7 +20,8 @@
 import java.util.OptionalLong;
 
 /**
- * An interface to represent statistics for a data source.
+ * An interface to represent statistics for a data source, which is returned by
+ * `SupportsReportStatistics`.
  */
 public interface Statistics {
   OptionalLong sizeInBytes();