Github user cloud-fan commented on a diff in the pull request:
https://github.com/apache/spark/pull/20153#discussion_r161362565
--- Diff:
sql/core/src/test/java/test/org/apache/spark/sql/sources/v2/JavaBatchDataSourceV2.java
---
@@ -0,0 +1,112 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements. See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License. You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package test.org.apache.spark.sql.sources.v2;
+
+import java.io.IOException;
+import java.util.List;
+
+import org.apache.spark.sql.execution.vectorized.OnHeapColumnVector;
+import org.apache.spark.sql.sources.v2.DataSourceV2;
+import org.apache.spark.sql.sources.v2.DataSourceV2Options;
+import org.apache.spark.sql.sources.v2.ReadSupport;
+import org.apache.spark.sql.sources.v2.reader.*;
+import org.apache.spark.sql.types.DataTypes;
+import org.apache.spark.sql.types.StructType;
+import org.apache.spark.sql.vectorized.ColumnVector;
+import org.apache.spark.sql.vectorized.ColumnarBatch;
+
+
+public class JavaBatchDataSourceV2 implements DataSourceV2, ReadSupport {
+
+ class Reader implements DataSourceV2Reader, SupportsScanColumnarBatch {
--- End diff --
This is the convention. If we implement many mix-in interfaces, it's better
to write
```
MyReader extends DataSourceV2Reader, XXX, YYY, ZZZ ...
```
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