Github user JoshRosen commented on a diff in the pull request:
https://github.com/apache/spark/pull/2696#discussion_r18867651
--- Diff: core/src/main/java/org/apache/spark/SparkJobInfo.java ---
@@ -0,0 +1,30 @@
+/*
+ * 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;
+
+/**
+ * Exposes information about Spark Jobs.
+ *
+ * This interface is not designed to be implemented outside of Spark. We
may add additional methods
--- End diff --
I think that exposing interfaces helps to maximize the flexibility of our
internal implementations of Java-friendly classes. Imagine that I want to have
a `private[spark]` method on an object that I expose to users. If I implement
this as a Scala class, my `private[spark]` methods and fields are public from
Java users' points of view. If I implement this as a `public final class` Java
with package-private methods, then I need to add a separate class containing
"forwarder" methods in order to allow the Java package-private methods to be
called from Scala subpackages.
The need for this kind of flexibility isn't much of a concern for this
specific case, since SparkJobInfo and SparkStageInfo are simple immutable
objects, but it _is_ a problem for classes like TaskContext. Since other
Java-friendly APIs will likely be exposed as interfaces, I was thinking of
doing the same here for consistency's sake.
Does this sound reasonable or are there other approaches / considerations
that I'm missing?
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