[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.

3 files changed, 6 insertions, 8 deletions

diff --git a/examples/src/main/scala/org/apache/spark/examples/mllib/StreamingTestExample.scala b/examples/src/main/scala/org/apache/spark/examples/mllib/StreamingTestExample.scala
index 49f5df3944..ae4dee24c6 100644
--- a/examples/src/main/scala/org/apache/spark/examples/mllib/StreamingTestExample.scala
+++ b/examples/src/main/scala/org/apache/spark/examples/mllib/StreamingTestExample.scala
@@ -59,10 +59,10 @@ object StreamingTestExample {
 
     val conf = new SparkConf().setMaster("local").setAppName("StreamingTestExample")
     val ssc = new StreamingContext(conf, batchDuration)
-    ssc.checkpoint({
+    ssc.checkpoint {
       val dir = Utils.createTempDir()
       dir.toString
-    })
+    }
 
     // $example on$
     val data = ssc.textFileStream(dataDir).map(line => line.split(",") match {
diff --git a/examples/src/main/scala/org/apache/spark/examples/streaming/RecoverableNetworkWordCount.scala b/examples/src/main/scala/org/apache/spark/examples/streaming/RecoverableNetworkWordCount.scala
index bb2af9cd72..aa762b27dc 100644
--- a/examples/src/main/scala/org/apache/spark/examples/streaming/RecoverableNetworkWordCount.scala
+++ b/examples/src/main/scala/org/apache/spark/examples/streaming/RecoverableNetworkWordCount.scala
@@ -115,8 +115,8 @@ object RecoverableNetworkWordCount {
     // words in input stream of \n delimited text (eg. generated by 'nc')
     val lines = ssc.socketTextStream(ip, port)
     val words = lines.flatMap(_.split(" "))
-    val wordCounts = words.map(x => (x, 1)).reduceByKey(_ + _)
-    wordCounts.foreachRDD { (rdd: RDD[(String, Int)], time: Time) =>
+    val wordCounts = words.map((_, 1)).reduceByKey(_ + _)
+    wordCounts.foreachRDD { (rdd, time) =>
       // Get or register the blacklist Broadcast
       val blacklist = WordBlacklist.getInstance(rdd.sparkContext)
       // Get or register the droppedWordsCounter Accumulator
@@ -158,9 +158,7 @@ object RecoverableNetworkWordCount {
     }
     val Array(ip, IntParam(port), checkpointDirectory, outputPath) = args
     val ssc = StreamingContext.getOrCreate(checkpointDirectory,
-      () => {
-        createContext(ip, port, outputPath, checkpointDirectory)
-      })
+      () => createContext(ip, port, outputPath, checkpointDirectory))
     ssc.start()
     ssc.awaitTermination()
   }
diff --git a/examples/src/main/scala/org/apache/spark/examples/streaming/SqlNetworkWordCount.scala b/examples/src/main/scala/org/apache/spark/examples/streaming/SqlNetworkWordCount.scala
index 918e124065..ad6a89e320 100644
--- a/examples/src/main/scala/org/apache/spark/examples/streaming/SqlNetworkWordCount.scala
+++ b/examples/src/main/scala/org/apache/spark/examples/streaming/SqlNetworkWordCount.scala
@@ -59,7 +59,7 @@ object SqlNetworkWordCount {
     val words = lines.flatMap(_.split(" "))
 
     // Convert RDDs of the words DStream to DataFrame and run SQL query
-    words.foreachRDD { (rdd: RDD[String], time: Time) =>
+    words.foreachRDD { (rdd, time) =>
       // Get the singleton instance of SQLContext
       val sqlContext = SQLContextSingleton.getInstance(rdd.sparkContext)
       import sqlContext.implicits._