[SPARK-6428] Turn on explicit type checking for public methods.

This builds on my earlier pull requests and turns on the explicit type checking in scalastyle.

Author: Reynold Xin <rxin@databricks.com>

Closes #5342 from rxin/SPARK-6428 and squashes the following commits:

7b531ab [Reynold Xin] import ordering
2d9a8a5 [Reynold Xin] jl
e668b1c [Reynold Xin] override
9b9e119 [Reynold Xin] Parenthesis.
82e0cf5 [Reynold Xin] [SPARK-6428] Turn on explicit type checking for public methods.

11 files changed, 22 insertions, 19 deletions

diff --git a/examples/src/main/scala/org/apache/spark/examples/LocalKMeans.scala b/examples/src/main/scala/org/apache/spark/examples/LocalKMeans.scala
index 17624c20cf..f73eac1e2b 100644
--- a/examples/src/main/scala/org/apache/spark/examples/LocalKMeans.scala
+++ b/examples/src/main/scala/org/apache/spark/examples/LocalKMeans.scala
@@ -40,8 +40,8 @@ object LocalKMeans {
   val convergeDist = 0.001
   val rand = new Random(42)
 
-  def generateData = {
-    def generatePoint(i: Int) = {
+  def generateData: Array[DenseVector[Double]] = {
+    def generatePoint(i: Int): DenseVector[Double] = {
       DenseVector.fill(D){rand.nextDouble * R}
     }
     Array.tabulate(N)(generatePoint)
diff --git a/examples/src/main/scala/org/apache/spark/examples/LocalLR.scala b/examples/src/main/scala/org/apache/spark/examples/LocalLR.scala
index 92a683ad57..a55e0dc8d3 100644
--- a/examples/src/main/scala/org/apache/spark/examples/LocalLR.scala
+++ b/examples/src/main/scala/org/apache/spark/examples/LocalLR.scala
@@ -37,8 +37,8 @@ object LocalLR {
 
   case class DataPoint(x: Vector[Double], y: Double)
 
-  def generateData = {
-    def generatePoint(i: Int) = {
+  def generateData: Array[DataPoint] = {
+    def generatePoint(i: Int): DataPoint = {
       val y = if(i % 2 == 0) -1 else 1
       val x = DenseVector.fill(D){rand.nextGaussian + y * R}
       DataPoint(x, y)
diff --git a/examples/src/main/scala/org/apache/spark/examples/LogQuery.scala b/examples/src/main/scala/org/apache/spark/examples/LogQuery.scala
index 74620ad007..32e02eab8b 100644
--- a/examples/src/main/scala/org/apache/spark/examples/LogQuery.scala
+++ b/examples/src/main/scala/org/apache/spark/examples/LogQuery.scala
@@ -54,8 +54,8 @@ object LogQuery {
     // scalastyle:on
     /** Tracks the total query count and number of aggregate bytes for a particular group. */
     class Stats(val count: Int, val numBytes: Int) extends Serializable {
-      def merge(other: Stats) = new Stats(count + other.count, numBytes + other.numBytes)
-      override def toString = "bytes=%s\tn=%s".format(numBytes, count)
+      def merge(other: Stats): Stats = new Stats(count + other.count, numBytes + other.numBytes)
+      override def toString: String = "bytes=%s\tn=%s".format(numBytes, count)
     }
 
     def extractKey(line: String): (String, String, String) = {
diff --git a/examples/src/main/scala/org/apache/spark/examples/SparkLR.scala b/examples/src/main/scala/org/apache/spark/examples/SparkLR.scala
index 257a7d29f9..8c01a60844 100644
--- a/examples/src/main/scala/org/apache/spark/examples/SparkLR.scala
+++ b/examples/src/main/scala/org/apache/spark/examples/SparkLR.scala
@@ -42,8 +42,8 @@ object SparkLR {
 
   case class DataPoint(x: Vector[Double], y: Double)
 
-  def generateData = {
-    def generatePoint(i: Int) = {
+  def generateData: Array[DataPoint] = {
+    def generatePoint(i: Int): DataPoint = {
       val y = if(i % 2 == 0) -1 else 1
       val x = DenseVector.fill(D){rand.nextGaussian + y * R}
       DataPoint(x, y)
diff --git a/examples/src/main/scala/org/apache/spark/examples/SparkTC.scala b/examples/src/main/scala/org/apache/spark/examples/SparkTC.scala
index f7f83086df..772cd897f5 100644
--- a/examples/src/main/scala/org/apache/spark/examples/SparkTC.scala
+++ b/examples/src/main/scala/org/apache/spark/examples/SparkTC.scala
@@ -31,7 +31,7 @@ object SparkTC {
   val numVertices = 100
   val rand = new Random(42)
 
-  def generateGraph = {
+  def generateGraph: Seq[(Int, Int)] = {
     val edges: mutable.Set[(Int, Int)] = mutable.Set.empty
     while (edges.size < numEdges) {
       val from = rand.nextInt(numVertices)
diff --git a/examples/src/main/scala/org/apache/spark/examples/bagel/PageRankUtils.scala b/examples/src/main/scala/org/apache/spark/examples/bagel/PageRankUtils.scala
index e322d4ce5a..ab6e63deb3 100644
--- a/examples/src/main/scala/org/apache/spark/examples/bagel/PageRankUtils.scala
+++ b/examples/src/main/scala/org/apache/spark/examples/bagel/PageRankUtils.scala
@@ -90,7 +90,7 @@ class PRMessage() extends Message[String] with Serializable {
 }
 
 class CustomPartitioner(partitions: Int) extends Partitioner {
-  def numPartitions = partitions
+  def numPartitions: Int = partitions
 
   def getPartition(key: Any): Int = {
     val hash = key match {
diff --git a/examples/src/main/scala/org/apache/spark/examples/mllib/MovieLensALS.scala b/examples/src/main/scala/org/apache/spark/examples/mllib/MovieLensALS.scala
index 1f4ca4fbe7..0bc36ea65e 100644
--- a/examples/src/main/scala/org/apache/spark/examples/mllib/MovieLensALS.scala
+++ b/examples/src/main/scala/org/apache/spark/examples/mllib/MovieLensALS.scala
@@ -178,7 +178,9 @@ object MovieLensALS {
   def computeRmse(model: MatrixFactorizationModel, data: RDD[Rating], implicitPrefs: Boolean)
     : Double = {
 
-    def mapPredictedRating(r: Double) = if (implicitPrefs) math.max(math.min(r, 1.0), 0.0) else r
+    def mapPredictedRating(r: Double): Double = {
+      if (implicitPrefs) math.max(math.min(r, 1.0), 0.0) else r
+    }
 
     val predictions: RDD[Rating] = model.predict(data.map(x => (x.user, x.product)))
     val predictionsAndRatings = predictions.map{ x =>
diff --git a/examples/src/main/scala/org/apache/spark/examples/streaming/ActorWordCount.scala b/examples/src/main/scala/org/apache/spark/examples/streaming/ActorWordCount.scala
index b433082dce..92867b44be 100644
--- a/examples/src/main/scala/org/apache/spark/examples/streaming/ActorWordCount.scala
+++ b/examples/src/main/scala/org/apache/spark/examples/streaming/ActorWordCount.scala
@@ -85,13 +85,13 @@ extends Actor with ActorHelper {
 
   lazy private val remotePublisher = context.actorSelection(urlOfPublisher)
 
-  override def preStart = remotePublisher ! SubscribeReceiver(context.self)
+  override def preStart(): Unit = remotePublisher ! SubscribeReceiver(context.self)
 
-  def receive = {
+  def receive: PartialFunction[Any, Unit] = {
     case msg => store(msg.asInstanceOf[T])
   }
 
-  override def postStop() = remotePublisher ! UnsubscribeReceiver(context.self)
+  override def postStop(): Unit = remotePublisher ! UnsubscribeReceiver(context.self)
 
 }
 
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 c3a05c89d8..751b30ea15 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
@@ -55,7 +55,8 @@ import org.apache.spark.util.IntParam
  */
 object RecoverableNetworkWordCount {
 
-  def createContext(ip: String, port: Int, outputPath: String, checkpointDirectory: String) = {
+  def createContext(ip: String, port: Int, outputPath: String, checkpointDirectory: String)
+    : StreamingContext = {
 
     // If you do not see this printed, that means the StreamingContext has been loaded
     // from the new checkpoint
diff --git a/examples/src/main/scala/org/apache/spark/examples/streaming/ZeroMQWordCount.scala b/examples/src/main/scala/org/apache/spark/examples/streaming/ZeroMQWordCount.scala
index 6510c70bd1..e99d1baa72 100644
--- a/examples/src/main/scala/org/apache/spark/examples/streaming/ZeroMQWordCount.scala
+++ b/examples/src/main/scala/org/apache/spark/examples/streaming/ZeroMQWordCount.scala
@@ -35,7 +35,7 @@ import org.apache.spark.SparkConf
  */
 object SimpleZeroMQPublisher {
 
-  def main(args: Array[String]) = {
+  def main(args: Array[String]): Unit = {
     if (args.length < 2) {
       System.err.println("Usage: SimpleZeroMQPublisher <zeroMQUrl> <topic> ")
       System.exit(1)
@@ -45,7 +45,7 @@ object SimpleZeroMQPublisher {
     val acs: ActorSystem = ActorSystem()
 
     val pubSocket = ZeroMQExtension(acs).newSocket(SocketType.Pub, Bind(url))
-    implicit def stringToByteString(x: String) = ByteString(x)
+    implicit def stringToByteString(x: String): ByteString = ByteString(x)
     val messages: List[ByteString] = List("words ", "may ", "count ")
     while (true) {
       Thread.sleep(1000)
@@ -86,7 +86,7 @@ object ZeroMQWordCount {
     // Create the context and set the batch size
     val ssc = new StreamingContext(sparkConf, Seconds(2))
 
-    def bytesToStringIterator(x: Seq[ByteString]) = (x.map(_.utf8String)).iterator
+    def bytesToStringIterator(x: Seq[ByteString]): Iterator[String] = x.map(_.utf8String).iterator
 
     // For this stream, a zeroMQ publisher should be running.
     val lines = ZeroMQUtils.createStream(ssc, url, Subscribe(topic), bytesToStringIterator _)
diff --git a/examples/src/main/scala/org/apache/spark/examples/streaming/clickstream/PageViewGenerator.scala b/examples/src/main/scala/org/apache/spark/examples/streaming/clickstream/PageViewGenerator.scala
index 8402491b62..54d996b8ac 100644
--- a/examples/src/main/scala/org/apache/spark/examples/streaming/clickstream/PageViewGenerator.scala
+++ b/examples/src/main/scala/org/apache/spark/examples/streaming/clickstream/PageViewGenerator.scala
@@ -94,7 +94,7 @@ object PageViewGenerator {
     while (true) {
       val socket = listener.accept()
       new Thread() {
-        override def run = {
+        override def run(): Unit = {
           println("Got client connected from: " + socket.getInetAddress)
           val out = new PrintWriter(socket.getOutputStream(), true)