[MINOR] Remove inappropriate type notation and extra anonymous closure within functional transformations

## What changes were proposed in this pull request?

This PR removes

- Inappropriate type notations
    For example, from
    ```scala
    words.foreachRDD { (rdd: RDD[String], time: Time) =>
    ...
    ```
    to
    ```scala
    words.foreachRDD { (rdd, time) =>
    ...
    ```

- Extra anonymous closure within functional transformations.
    For example,
    ```scala
    .map(item => {
      ...
    })
    ```

    which can be just simply as below:

    ```scala
    .map { item =>
      ...
    }
    ```

and corrects some obvious style nits.

## How was this patch tested?

This was tested after adding rules in `scalastyle-config.xml`, which ended up with not finding all perfectly.

The rules applied were below:

- For the first correction,

```xml
<check customId="NoExtraClosure" level="error" class="org.scalastyle.file.RegexChecker" enabled="true">
    <parameters><parameter name="regex">(?m)\.[a-zA-Z_][a-zA-Z0-9]*\(\s*[^,]+s*=>\s*\{[^\}]+\}\s*\)</parameter></parameters>
</check>
```

```xml
<check customId="NoExtraClosure" level="error" class="org.scalastyle.file.RegexChecker" enabled="true">
    <parameters><parameter name="regex">\.[a-zA-Z_][a-zA-Z0-9]*\s*[\{|\(]([^\n>,]+=>)?\s*\{([^()]|(?R))*\}^[,]</parameter></parameters>
</check>
```

- For the second correction
```xml
<check customId="TypeNotation" level="error" class="org.scalastyle.file.RegexChecker" enabled="true">
    <parameters><parameter name="regex">\.[a-zA-Z_][a-zA-Z0-9]*\s*[\{|\(]\s*\([^):]*:R))*\}^[,]</parameter></parameters>
</check>
```

**Those rules were not added**

Author: hyukjinkwon <gurwls223@gmail.com>

Closes #12413 from HyukjinKwon/SPARK-style.

1 files changed, 8 insertions, 8 deletions

diff --git a/streaming/src/main/scala/org/apache/spark/streaming/dstream/DStream.scala b/streaming/src/main/scala/org/apache/spark/streaming/dstream/DStream.scala
index 58842f9c2f..583f5a48d1 100644
--- a/streaming/src/main/scala/org/apache/spark/streaming/dstream/DStream.scala
+++ b/streaming/src/main/scala/org/apache/spark/streaming/dstream/DStream.scala
@@ -593,7 +593,7 @@ abstract class DStream[T: ClassTag] (
    * of this DStream.
    */
   def reduce(reduceFunc: (T, T) => T): DStream[T] = ssc.withScope {
-    this.map(x => (null, x)).reduceByKey(reduceFunc, 1).map(_._2)
+    this.map((null, _)).reduceByKey(reduceFunc, 1).map(_._2)
   }
 
   /**
@@ -615,7 +615,7 @@ abstract class DStream[T: ClassTag] (
    */
   def countByValue(numPartitions: Int = ssc.sc.defaultParallelism)(implicit ord: Ordering[T] = null)
       : DStream[(T, Long)] = ssc.withScope {
-    this.map(x => (x, 1L)).reduceByKey((x: Long, y: Long) => x + y, numPartitions)
+    this.map((_, 1L)).reduceByKey((x: Long, y: Long) => x + y, numPartitions)
   }
 
   /**
@@ -624,7 +624,7 @@ abstract class DStream[T: ClassTag] (
    */
   def foreachRDD(foreachFunc: RDD[T] => Unit): Unit = ssc.withScope {
     val cleanedF = context.sparkContext.clean(foreachFunc, false)
-    foreachRDD((r: RDD[T], t: Time) => cleanedF(r), displayInnerRDDOps = true)
+    foreachRDD((r: RDD[T], _: Time) => cleanedF(r), displayInnerRDDOps = true)
   }
 
   /**
@@ -663,7 +663,7 @@ abstract class DStream[T: ClassTag] (
     // DStreams can't be serialized with closures, we can't proactively check
     // it for serializability and so we pass the optional false to SparkContext.clean
     val cleanedF = context.sparkContext.clean(transformFunc, false)
-    transform((r: RDD[T], t: Time) => cleanedF(r))
+    transform((r: RDD[T], _: Time) => cleanedF(r))
   }
 
   /**
@@ -806,7 +806,7 @@ abstract class DStream[T: ClassTag] (
       windowDuration: Duration,
       slideDuration: Duration
     ): DStream[T] = ssc.withScope {
-      this.map(x => (1, x))
+      this.map((1, _))
           .reduceByKeyAndWindow(reduceFunc, invReduceFunc, windowDuration, slideDuration, 1)
           .map(_._2)
   }
@@ -845,7 +845,7 @@ abstract class DStream[T: ClassTag] (
       numPartitions: Int = ssc.sc.defaultParallelism)
       (implicit ord: Ordering[T] = null)
       : DStream[(T, Long)] = ssc.withScope {
-    this.map(x => (x, 1L)).reduceByKeyAndWindow(
+    this.map((_, 1L)).reduceByKeyAndWindow(
       (x: Long, y: Long) => x + y,
       (x: Long, y: Long) => x - y,
       windowDuration,
@@ -895,9 +895,9 @@ abstract class DStream[T: ClassTag] (
     logInfo(s"Slicing from $fromTime to $toTime" +
       s" (aligned to $alignedFromTime and $alignedToTime)")
 
-    alignedFromTime.to(alignedToTime, slideDuration).flatMap(time => {
+    alignedFromTime.to(alignedToTime, slideDuration).flatMap { time =>
       if (time >= zeroTime) getOrCompute(time) else None
-    })
+    }
   }
 
   /**