[SPARK-14465][BUILD] Checkstyle should check all Java files

## What changes were proposed in this pull request?

Currently, `checkstyle` is configured to check the files under `src/main/java`. However, Spark has Java files in `src/main/scala`, too. This PR fixes the following configuration in `pom.xml` and the unchecked-so-far violations on those files.
```xml
-<sourceDirectory>${basedir}/src/main/java</sourceDirectory>
+<sourceDirectories>${basedir}/src/main/java,${basedir}/src/main/scala</sourceDirectories>
```

## How was this patch tested?

After passing the Jenkins build and manually `dev/lint-java`. (Note that Jenkins does not run `lint-java`)

Author: Dongjoon Hyun <dongjoon@apache.org>

Closes #12242 from dongjoon-hyun/SPARK-14465.

1 files changed, 4 insertions, 2 deletions

diff --git a/external/java8-tests/src/test/java/org/apache/spark/streaming/Java8APISuite.java b/external/java8-tests/src/test/java/org/apache/spark/streaming/Java8APISuite.java
index 67bc64a444..d0fed303e6 100644
--- a/external/java8-tests/src/test/java/org/apache/spark/streaming/Java8APISuite.java
+++ b/external/java8-tests/src/test/java/org/apache/spark/streaming/Java8APISuite.java
@@ -377,7 +377,9 @@ public class Java8APISuite extends LocalJavaStreamingContext implements Serializ
     });
 
     // This is a test to make sure foreachRDD(VoidFunction2) can be called from Java
-    stream.foreachRDD((rdd, time) -> { return; });
+    stream.foreachRDD((rdd, time) -> {
+      return;
+    });
 
     JavaTestUtils.runStreams(ssc, 2, 2);
 
@@ -873,7 +875,7 @@ public class Java8APISuite extends LocalJavaStreamingContext implements Serializ
 
     JavaMapWithStateDStream<String, Integer, Boolean, Double> stateDstream =
         wordsDstream.mapWithState(
-            StateSpec.<String, Integer, Boolean, Double> function((time, key, value, state) -> {
+            StateSpec.<String, Integer, Boolean, Double>function((time, key, value, state) -> {
               // Use all State's methods here
               state.exists();
               state.get();