Github user tdas commented on a diff in the pull request:
https://github.com/apache/spark/pull/13286#discussion_r64980368
--- Diff: sql/catalyst/src/main/java/org/apache/spark/sql/OutputMode.java
---
@@ -0,0 +1,54 @@
+/*
+ * 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 org.apache.spark.sql;
+
+import org.apache.spark.annotation.Experimental;
+
+/**
+ * :: Experimental ::
+ *
+ * OutputMode is used to what data will be written to a streaming sink
when there is
+ * new data available in a streaming DataFrame/Dataset.
+ *
+ * @since 2.0.0
+ */
+@Experimental
+public class OutputMode {
--- End diff --
Okay, writing it in Scala does not work because we need define static
methods on OutputMode ('Append()', etc.) as well as the OutputMode interface
that singleton object Append will extend. To do this in Scala we have to do
```
trait OutputMode
object OutputMode {
def Append(): OutputMode = ???
}
```
But this makes the OutputMode static object unusable from Java, as you will
have to call `OutputMode$.MODULE$.Append()`.
So doing this in Java is the cleanest way for it to be usable in both Java
and Scala. I am including a JavaOutputModeSuite as well.
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