diff --git a/core/src/main/scala/org/apache/spark/SSLOptions.scala b/core/src/main/scala/org/apache/spark/SSLOptions.scala
index f86fd20e59..477b01968c 100644
--- a/core/src/main/scala/org/apache/spark/SSLOptions.scala
+++ b/core/src/main/scala/org/apache/spark/SSLOptions.scala
@@ -94,21 +94,23 @@ private[spark] case class SSLOptions(
    * are supported by the current Java security provider for this protocol.
    */
   private val supportedAlgorithms: Set[String] = if (enabledAlgorithms.isEmpty) {
-    Set()
+    Set.empty
   } else {
     var context: SSLContext = null
-    try {
-      context = SSLContext.getInstance(protocol.orNull)
-      /* The set of supported algorithms does not depend upon the keys, trust, or
+    if (protocol.isEmpty) {
+      logDebug("No SSL protocol specified")
+      context = SSLContext.getDefault
+    } else {
+      try {
+        context = SSLContext.getInstance(protocol.get)
+        /* The set of supported algorithms does not depend upon the keys, trust, or
          rng, although they will influence which algorithms are eventually used. */
-      context.init(null, null, null)
-    } catch {
-      case npe: NullPointerException =>
-        logDebug("No SSL protocol specified")
-        context = SSLContext.getDefault
-      case nsa: NoSuchAlgorithmException =>
-        logDebug(s"No support for requested SSL protocol ${protocol.get}")
-        context = SSLContext.getDefault
+        context.init(null, null, null)
+      } catch {
+        case nsa: NoSuchAlgorithmException =>
+          logDebug(s"No support for requested SSL protocol ${protocol.get}")
+          context = SSLContext.getDefault
+      }
     }
 
     val providerAlgorithms = context.getServerSocketFactory.getSupportedCipherSuites.toSet
diff --git a/core/src/main/scala/org/apache/spark/SparkEnv.scala b/core/src/main/scala/org/apache/spark/SparkEnv.scala
index 3196c1ece1..45ed9860ea 100644
--- a/core/src/main/scala/org/apache/spark/SparkEnv.scala
+++ b/core/src/main/scala/org/apache/spark/SparkEnv.scala
@@ -420,7 +420,7 @@ object SparkEnv extends Logging {
       if (!conf.contains("spark.scheduler.mode")) {
         Seq(("spark.scheduler.mode", schedulingMode))
       } else {
-        Seq[(String, String)]()
+        Seq.empty[(String, String)]
       }
     val sparkProperties = (conf.getAll ++ schedulerMode).sorted
 
diff --git a/core/src/main/scala/org/apache/spark/TestUtils.scala b/core/src/main/scala/org/apache/spark/TestUtils.scala
index 3f912dc191..a80016dd22 100644
--- a/core/src/main/scala/org/apache/spark/TestUtils.scala
+++ b/core/src/main/scala/org/apache/spark/TestUtils.scala
@@ -58,8 +58,8 @@ private[spark] object TestUtils {
   def createJarWithClasses(
       classNames: Seq[String],
       toStringValue: String = "",
-      classNamesWithBase: Seq[(String, String)] = Seq(),
-      classpathUrls: Seq[URL] = Seq()): URL = {
+      classNamesWithBase: Seq[(String, String)] = Seq.empty,
+      classpathUrls: Seq[URL] = Seq.empty): URL = {
     val tempDir = Utils.createTempDir()
     val files1 = for (name <- classNames) yield {
       createCompiledClass(name, tempDir, toStringValue, classpathUrls = classpathUrls)
@@ -137,7 +137,7 @@ private[spark] object TestUtils {
     val options = if (classpathUrls.nonEmpty) {
       Seq("-classpath", classpathUrls.map { _.getFile }.mkString(File.pathSeparator))
     } else {
-      Seq()
+      Seq.empty
     }
     compiler.getTask(null, null, null, options.asJava, null, Arrays.asList(sourceFile)).call()
 
@@ -160,7 +160,7 @@ private[spark] object TestUtils {
       destDir: File,
       toStringValue: String = "",
       baseClass: String = null,
-      classpathUrls: Seq[URL] = Seq()): File = {
+      classpathUrls: Seq[URL] = Seq.empty): File = {
     val extendsText = Option(baseClass).map { c => s" extends ${c}" }.getOrElse("")
     val sourceFile = new JavaSourceFromString(className,
       "public class " + className + extendsText + " implements java.io.Serializable {" +
diff --git a/core/src/main/scala/org/apache/spark/api/python/PythonRDD.scala b/core/src/main/scala/org/apache/spark/api/python/PythonRDD.scala
index fb0405b1a6..6a81752400 100644
--- a/core/src/main/scala/org/apache/spark/api/python/PythonRDD.scala
+++ b/core/src/main/scala/org/apache/spark/api/python/PythonRDD.scala
@@ -974,6 +974,7 @@ private[spark] class PythonBroadcast(@transient var path: String) extends Serial
         }
       }
     }
+    super.finalize()
   }
 }
 // scalastyle:on no.finalize
diff --git a/core/src/main/scala/org/apache/spark/api/r/SerDe.scala b/core/src/main/scala/org/apache/spark/api/r/SerDe.scala
index dad928cdcf..537ab57f96 100644
--- a/core/src/main/scala/org/apache/spark/api/r/SerDe.scala
+++ b/core/src/main/scala/org/apache/spark/api/r/SerDe.scala
@@ -128,8 +128,7 @@ private[spark] object SerDe {
   }
 
   def readBoolean(in: DataInputStream): Boolean = {
-    val intVal = in.readInt()
-    if (intVal == 0) false else true
+    in.readInt() != 0
   }
 
   def readDate(in: DataInputStream): Date = {
diff --git a/core/src/main/scala/org/apache/spark/deploy/SparkHadoopUtil.scala b/core/src/main/scala/org/apache/spark/deploy/SparkHadoopUtil.scala
index 6afe58bff5..ccbabf09a8 100644
--- a/core/src/main/scala/org/apache/spark/deploy/SparkHadoopUtil.scala
+++ b/core/src/main/scala/org/apache/spark/deploy/SparkHadoopUtil.scala
@@ -337,7 +337,7 @@ class SparkHadoopUtil extends Logging {
     if (credentials != null) {
       credentials.getAllTokens.asScala.map(tokenToString)
     } else {
-      Seq()
+      Seq.empty
     }
   }
 
diff --git a/core/src/main/scala/org/apache/spark/deploy/history/FsHistoryProvider.scala b/core/src/main/scala/org/apache/spark/deploy/history/FsHistoryProvider.scala
index b2a50bd055..687fd2d3ff 100644
--- a/core/src/main/scala/org/apache/spark/deploy/history/FsHistoryProvider.scala
+++ b/core/src/main/scala/org/apache/spark/deploy/history/FsHistoryProvider.scala
@@ -317,7 +317,7 @@ private[history] class FsHistoryProvider(conf: SparkConf, clock: Clock)
       val newLastScanTime = getNewLastScanTime()
       logDebug(s"Scanning $logDir with lastScanTime==$lastScanTime")
       val statusList = Option(fs.listStatus(new Path(logDir))).map(_.toSeq)
-        .getOrElse(Seq[FileStatus]())
+        .getOrElse(Seq.empty[FileStatus])
       // scan for modified applications, replay and merge them
       val logInfos: Seq[FileStatus] = statusList
         .filter { entry =>
diff --git a/core/src/main/scala/org/apache/spark/deploy/master/ui/MasterWebUI.scala b/core/src/main/scala/org/apache/spark/deploy/master/ui/MasterWebUI.scala
index 8cfd0f6829..e42f41b972 100644
--- a/core/src/main/scala/org/apache/spark/deploy/master/ui/MasterWebUI.scala
+++ b/core/src/main/scala/org/apache/spark/deploy/master/ui/MasterWebUI.scala
@@ -55,7 +55,7 @@ class MasterWebUI(
   }
 
   def addProxyTargets(id: String, target: String): Unit = {
-    var endTarget = target.stripSuffix("/")
+    val endTarget = target.stripSuffix("/")
     val handler = createProxyHandler("/proxy/" + id, endTarget)
     attachHandler(handler)
     proxyHandlers(id) = handler
diff --git a/core/src/main/scala/org/apache/spark/deploy/worker/CommandUtils.scala b/core/src/main/scala/org/apache/spark/deploy/worker/CommandUtils.scala
index cba4aaffe2..12e0dae3f5 100644
--- a/core/src/main/scala/org/apache/spark/deploy/worker/CommandUtils.scala
+++ b/core/src/main/scala/org/apache/spark/deploy/worker/CommandUtils.scala
@@ -44,7 +44,7 @@ object CommandUtils extends Logging {
       memory: Int,
       sparkHome: String,
       substituteArguments: String => String,
-      classPaths: Seq[String] = Seq[String](),
+      classPaths: Seq[String] = Seq.empty,
       env: Map[String, String] = sys.env): ProcessBuilder = {
     val localCommand = buildLocalCommand(
       command, securityMgr, substituteArguments, classPaths, env)
@@ -73,7 +73,7 @@ object CommandUtils extends Logging {
       command: Command,
       securityMgr: SecurityManager,
       substituteArguments: String => String,
-      classPath: Seq[String] = Seq[String](),
+      classPath: Seq[String] = Seq.empty,
       env: Map[String, String]): Command = {
     val libraryPathName = Utils.libraryPathEnvName
     val libraryPathEntries = command.libraryPathEntries
@@ -96,7 +96,7 @@ object CommandUtils extends Logging {
       command.arguments.map(substituteArguments),
       newEnvironment,
       command.classPathEntries ++ classPath,
-      Seq[String](), // library path already captured in environment variable
+      Seq.empty, // library path already captured in environment variable
       // filter out auth secret from java options
       command.javaOpts.filterNot(_.startsWith("-D" + SecurityManager.SPARK_AUTH_SECRET_CONF)))
   }
diff --git a/core/src/main/scala/org/apache/spark/package.scala b/core/src/main/scala/org/apache/spark/package.scala
index 2610d6f6e4..8058a4d5db 100644
--- a/core/src/main/scala/org/apache/spark/package.scala
+++ b/core/src/main/scala/org/apache/spark/package.scala
@@ -17,6 +17,8 @@
 
 package org.apache
 
+import java.util.Properties
+
 /**
  * Core Spark functionality. [[org.apache.spark.SparkContext]] serves as the main entry point to
  * Spark, while [[org.apache.spark.rdd.RDD]] is the data type representing a distributed collection,
@@ -40,9 +42,6 @@ package org.apache
  * Developer API</span> are intended for advanced users want to extend Spark through lower
  * level interfaces. These are subject to changes or removal in minor releases.
  */
-
-import java.util.Properties
-
 package object spark {
 
   private object SparkBuildInfo {
@@ -57,6 +56,9 @@ package object spark {
 
       val resourceStream = Thread.currentThread().getContextClassLoader.
         getResourceAsStream("spark-version-info.properties")
+      if (resourceStream == null) {
+        throw new SparkException("Could not find spark-version-info.properties")
+      }
 
       try {
         val unknownProp = "<unknown>"
@@ -71,8 +73,6 @@ package object spark {
           props.getProperty("date", unknownProp)
         )
       } catch {
-        case npe: NullPointerException =>
-          throw new SparkException("Error while locating file spark-version-info.properties", npe)
         case e: Exception =>
           throw new SparkException("Error loading properties from spark-version-info.properties", e)
       } finally {
diff --git a/core/src/main/scala/org/apache/spark/rdd/CoalescedRDD.scala b/core/src/main/scala/org/apache/spark/rdd/CoalescedRDD.scala
index 2cba1febe8..10451a324b 100644
--- a/core/src/main/scala/org/apache/spark/rdd/CoalescedRDD.scala
+++ b/core/src/main/scala/org/apache/spark/rdd/CoalescedRDD.scala
@@ -269,7 +269,7 @@ private class DefaultPartitionCoalescer(val balanceSlack: Double = 0.10)
     tries = 0
     // if we don't have enough partition groups, create duplicates
     while (numCreated < targetLen) {
-      var (nxt_replica, nxt_part) = partitionLocs.partsWithLocs(tries)
+      val (nxt_replica, nxt_part) = partitionLocs.partsWithLocs(tries)
       tries += 1
       val pgroup = new PartitionGroup(Some(nxt_replica))
       groupArr += pgroup
diff --git a/core/src/main/scala/org/apache/spark/scheduler/Pool.scala b/core/src/main/scala/org/apache/spark/scheduler/Pool.scala
index 1181371ab4..f4b0ab1015 100644
--- a/core/src/main/scala/org/apache/spark/scheduler/Pool.scala
+++ b/core/src/main/scala/org/apache/spark/scheduler/Pool.scala
@@ -97,7 +97,7 @@ private[spark] class Pool(
   }
 
   override def getSortedTaskSetQueue: ArrayBuffer[TaskSetManager] = {
-    var sortedTaskSetQueue = new ArrayBuffer[TaskSetManager]
+    val sortedTaskSetQueue = new ArrayBuffer[TaskSetManager]
     val sortedSchedulableQueue =
       schedulableQueue.asScala.toSeq.sortWith(taskSetSchedulingAlgorithm.comparator)
     for (schedulable <- sortedSchedulableQueue) {
diff --git a/core/src/main/scala/org/apache/spark/scheduler/TaskResult.scala b/core/src/main/scala/org/apache/spark/scheduler/TaskResult.scala
index 366b92c5f2..836769e172 100644
--- a/core/src/main/scala/org/apache/spark/scheduler/TaskResult.scala
+++ b/core/src/main/scala/org/apache/spark/scheduler/TaskResult.scala
@@ -60,7 +60,7 @@ private[spark] class DirectTaskResult[T](
 
     val numUpdates = in.readInt
     if (numUpdates == 0) {
-      accumUpdates = Seq()
+      accumUpdates = Seq.empty
     } else {
       val _accumUpdates = new ArrayBuffer[AccumulatorV2[_, _]]
       for (i <- 0 until numUpdates) {
diff --git a/core/src/main/scala/org/apache/spark/scheduler/TaskSetManager.scala b/core/src/main/scala/org/apache/spark/scheduler/TaskSetManager.scala
index 3968fb7e63..589fe672ad 100644
--- a/core/src/main/scala/org/apache/spark/scheduler/TaskSetManager.scala
+++ b/core/src/main/scala/org/apache/spark/scheduler/TaskSetManager.scala
@@ -891,7 +891,7 @@ private[spark] class TaskSetManager(
   override def removeSchedulable(schedulable: Schedulable) {}
 
   override def getSortedTaskSetQueue(): ArrayBuffer[TaskSetManager] = {
-    var sortedTaskSetQueue = new ArrayBuffer[TaskSetManager]()
+    val sortedTaskSetQueue = new ArrayBuffer[TaskSetManager]()
     sortedTaskSetQueue += this
     sortedTaskSetQueue
   }
@@ -948,7 +948,7 @@ private[spark] class TaskSetManager(
 
     if (tasksSuccessful >= minFinishedForSpeculation && tasksSuccessful > 0) {
       val time = clock.getTimeMillis()
-      var medianDuration = successfulTaskDurations.median
+      val medianDuration = successfulTaskDurations.median
       val threshold = max(SPECULATION_MULTIPLIER * medianDuration, minTimeToSpeculation)
       // TODO: Threshold should also look at standard deviation of task durations and have a lower
       // bound based on that.
diff --git a/core/src/main/scala/org/apache/spark/scheduler/cluster/CoarseGrainedSchedulerBackend.scala b/core/src/main/scala/org/apache/spark/scheduler/cluster/CoarseGrainedSchedulerBackend.scala
index 0b396b794d..a46824a0c6 100644
--- a/core/src/main/scala/org/apache/spark/scheduler/cluster/CoarseGrainedSchedulerBackend.scala
+++ b/core/src/main/scala/org/apache/spark/scheduler/cluster/CoarseGrainedSchedulerBackend.scala
@@ -23,7 +23,6 @@ import javax.annotation.concurrent.GuardedBy
 
 import scala.collection.mutable.{ArrayBuffer, HashMap, HashSet}
 import scala.concurrent.Future
-import scala.concurrent.duration.Duration
 
 import org.apache.spark.{ExecutorAllocationClient, SparkEnv, SparkException, TaskState}
 import org.apache.spark.internal.Logging
@@ -427,11 +426,11 @@ class CoarseGrainedSchedulerBackend(scheduler: TaskSchedulerImpl, val rpcEnv: Rp
    * be called in the yarn-client mode when AM re-registers after a failure.
    * */
   protected def reset(): Unit = {
-    val executors = synchronized {
+    val executors: Set[String] = synchronized {
       requestedTotalExecutors = 0
       numPendingExecutors = 0
       executorsPendingToRemove.clear()
-      Set() ++ executorDataMap.keys
+      executorDataMap.keys.toSet
     }
 
     // Remove all the lingering executors that should be removed but not yet. The reason might be
diff --git a/core/src/main/scala/org/apache/spark/storage/BlockManager.scala b/core/src/main/scala/org/apache/spark/storage/BlockManager.scala
index adbe3cfd89..aaacabe79a 100644
--- a/core/src/main/scala/org/apache/spark/storage/BlockManager.scala
+++ b/core/src/main/scala/org/apache/spark/storage/BlockManager.scala
@@ -1275,11 +1275,11 @@ private[spark] class BlockManager(
     val numPeersToReplicateTo = level.replication - 1
     val startTime = System.nanoTime
 
-    var peersReplicatedTo = mutable.HashSet.empty ++ existingReplicas
-    var peersFailedToReplicateTo = mutable.HashSet.empty[BlockManagerId]
+    val peersReplicatedTo = mutable.HashSet.empty ++ existingReplicas
+    val peersFailedToReplicateTo = mutable.HashSet.empty[BlockManagerId]
     var numFailures = 0
 
-    val initialPeers = getPeers(false).filterNot(existingReplicas.contains(_))
+    val initialPeers = getPeers(false).filterNot(existingReplicas.contains)
 
     var peersForReplication = blockReplicationPolicy.prioritize(
       blockManagerId,
diff --git a/core/src/main/scala/org/apache/spark/ui/jobs/AllJobsPage.scala b/core/src/main/scala/org/apache/spark/ui/jobs/AllJobsPage.scala
index cce7a7611b..a7f2caafe0 100644
--- a/core/src/main/scala/org/apache/spark/ui/jobs/AllJobsPage.scala
+++ b/core/src/main/scala/org/apache/spark/ui/jobs/AllJobsPage.scala
@@ -241,7 +241,7 @@ private[ui] class AllJobsPage(parent: JobsTab) extends WebUIPage("") {
     }.getOrElse(jobIdTitle)
     val jobSortDesc = Option(parameterJobSortDesc).map(_.toBoolean).getOrElse(
       // New jobs should be shown above old jobs by default.
-      if (jobSortColumn == jobIdTitle) true else false
+      jobSortColumn == jobIdTitle
     )
     val jobPageSize = Option(parameterJobPageSize).map(_.toInt).getOrElse(100)
     val jobPrevPageSize = Option(parameterJobPrevPageSize).map(_.toInt).getOrElse(jobPageSize)
diff --git a/core/src/main/scala/org/apache/spark/ui/jobs/AllStagesPage.scala b/core/src/main/scala/org/apache/spark/ui/jobs/AllStagesPage.scala
index 2b0816e357..a30c135929 100644
--- a/core/src/main/scala/org/apache/spark/ui/jobs/AllStagesPage.scala
+++ b/core/src/main/scala/org/apache/spark/ui/jobs/AllStagesPage.scala
@@ -115,7 +115,7 @@ private[ui] class AllStagesPage(parent: StagesTab) extends WebUIPage("") {
           if (sc.isDefined && isFairScheduler) {
             <h4>{pools.size} Fair Scheduler Pools</h4> ++ poolTable.toNodeSeq
           } else {
-            Seq[Node]()
+            Seq.empty[Node]
           }
         }
       if (shouldShowActiveStages) {
diff --git a/core/src/main/scala/org/apache/spark/ui/jobs/PoolPage.scala b/core/src/main/scala/org/apache/spark/ui/jobs/PoolPage.scala
index b164f32b62..819fe57e14 100644
--- a/core/src/main/scala/org/apache/spark/ui/jobs/PoolPage.scala
+++ b/core/src/main/scala/org/apache/spark/ui/jobs/PoolPage.scala
@@ -41,7 +41,7 @@ private[ui] class PoolPage(parent: StagesTab) extends WebUIPage("pool") {
       val poolToActiveStages = listener.poolToActiveStages
       val activeStages = poolToActiveStages.get(poolName) match {
         case Some(s) => s.values.toSeq
-        case None => Seq[StageInfo]()
+        case None => Seq.empty[StageInfo]
       }
       val shouldShowActiveStages = activeStages.nonEmpty
       val activeStagesTable =
diff --git a/core/src/main/scala/org/apache/spark/ui/jobs/StagePage.scala b/core/src/main/scala/org/apache/spark/ui/jobs/StagePage.scala
index 6b3dadc333..8ed51746ab 100644
--- a/core/src/main/scala/org/apache/spark/ui/jobs/StagePage.scala
+++ b/core/src/main/scala/org/apache/spark/ui/jobs/StagePage.scala
@@ -565,7 +565,7 @@ private[ui] class StagePage(parent: StagesTab) extends WebUIPage("stage") {
       val executorTable = new ExecutorTable(stageId, stageAttemptId, parent)
 
       val maybeAccumulableTable: Seq[Node] =
-        if (hasAccumulators) { <h4>Accumulators</h4> ++ accumulableTable } else Seq()
+        if (hasAccumulators) { <h4>Accumulators</h4> ++ accumulableTable } else Seq.empty
 
       val aggMetrics =
         <span class="collapse-aggregated-metrics collapse-table"
diff --git a/core/src/main/scala/org/apache/spark/ui/jobs/StageTable.scala b/core/src/main/scala/org/apache/spark/ui/jobs/StageTable.scala
index a28daf7f90..f0a12a28de 100644
--- a/core/src/main/scala/org/apache/spark/ui/jobs/StageTable.scala
+++ b/core/src/main/scala/org/apache/spark/ui/jobs/StageTable.scala
@@ -60,7 +60,7 @@ private[ui] class StageTableBase(
   }.getOrElse("Stage Id")
   val stageSortDesc = Option(parameterStageSortDesc).map(_.toBoolean).getOrElse(
     // New stages should be shown above old jobs by default.
-    if (stageSortColumn == "Stage Id") true else false
+    stageSortColumn == "Stage Id"
   )
   val stagePageSize = Option(parameterStagePageSize).map(_.toInt).getOrElse(100)
   val stagePrevPageSize = Option(parameterStagePrevPageSize).map(_.toInt)
diff --git a/core/src/main/scala/org/apache/spark/ui/storage/RDDPage.scala b/core/src/main/scala/org/apache/spark/ui/storage/RDDPage.scala
index 317e0aa5ea..e8ff08f7d8 100644
--- a/core/src/main/scala/org/apache/spark/ui/storage/RDDPage.scala
+++ b/core/src/main/scala/org/apache/spark/ui/storage/RDDPage.scala
@@ -51,7 +51,7 @@ private[ui] class RDDPage(parent: StorageTab) extends WebUIPage("rdd") {
     val rddStorageInfo = AllRDDResource.getRDDStorageInfo(rddId, listener, includeDetails = true)
       .getOrElse {
         // Rather than crashing, render an "RDD Not Found" page
-        return UIUtils.headerSparkPage("RDD Not Found", Seq[Node](), parent)
+        return UIUtils.headerSparkPage("RDD Not Found", Seq.empty[Node], parent)
       }
 
     // Worker table
diff --git a/core/src/main/scala/org/apache/spark/util/ClosureCleaner.scala b/core/src/main/scala/org/apache/spark/util/ClosureCleaner.scala
index 489688cb08..48a1d7b84b 100644
--- a/core/src/main/scala/org/apache/spark/util/ClosureCleaner.scala
+++ b/core/src/main/scala/org/apache/spark/util/ClosureCleaner.scala
@@ -81,7 +81,7 @@ private[spark] object ClosureCleaner extends Logging {
     val stack = Stack[Class[_]](obj.getClass)
     while (!stack.isEmpty) {
       val cr = getClassReader(stack.pop())
-      val set = Set[Class[_]]()
+      val set = Set.empty[Class[_]]
       cr.accept(new InnerClosureFinder(set), 0)
       for (cls <- set -- seen) {
         seen += cls
@@ -180,16 +180,18 @@ private[spark] object ClosureCleaner extends Logging {
     val declaredFields = func.getClass.getDeclaredFields
     val declaredMethods = func.getClass.getDeclaredMethods
 
-    logDebug(" + declared fields: " + declaredFields.size)
-    declaredFields.foreach { f => logDebug("     " + f) }
-    logDebug(" + declared methods: " + declaredMethods.size)
-    declaredMethods.foreach { m => logDebug("     " + m) }
-    logDebug(" + inner classes: " + innerClasses.size)
-    innerClasses.foreach { c => logDebug("     " + c.getName) }
-    logDebug(" + outer classes: " + outerClasses.size)
-    outerClasses.foreach { c => logDebug("     " + c.getName) }
-    logDebug(" + outer objects: " + outerObjects.size)
-    outerObjects.foreach { o => logDebug("     " + o) }
+    if (log.isDebugEnabled) {
+      logDebug(" + declared fields: " + declaredFields.size)
+      declaredFields.foreach { f => logDebug("     " + f) }
+      logDebug(" + declared methods: " + declaredMethods.size)
+      declaredMethods.foreach { m => logDebug("     " + m) }
+      logDebug(" + inner classes: " + innerClasses.size)
+      innerClasses.foreach { c => logDebug("     " + c.getName) }
+      logDebug(" + outer classes: " + outerClasses.size)
+      outerClasses.foreach { c => logDebug("     " + c.getName) }
+      logDebug(" + outer objects: " + outerObjects.size)
+      outerObjects.foreach { o => logDebug("     " + o) }
+    }
 
     // Fail fast if we detect return statements in closures
     getClassReader(func.getClass).accept(new ReturnStatementFinder(), 0)
@@ -201,7 +203,7 @@ private[spark] object ClosureCleaner extends Logging {
       // Initialize accessed fields with the outer classes first
       // This step is needed to associate the fields to the correct classes later
       for (cls <- outerClasses) {
-        accessedFields(cls) = Set[String]()
+        accessedFields(cls) = Set.empty[String]
       }
       // Populate accessed fields by visiting all fields and methods accessed by this and
       // all of its inner closures. If transitive cleaning is enabled, this may recursively
diff --git a/core/src/main/scala/org/apache/spark/util/JsonProtocol.scala b/core/src/main/scala/org/apache/spark/util/JsonProtocol.scala
index 806d14e7cc..8406826a22 100644
--- a/core/src/main/scala/org/apache/spark/util/JsonProtocol.scala
+++ b/core/src/main/scala/org/apache/spark/util/JsonProtocol.scala
@@ -696,7 +696,7 @@ private[spark] object JsonProtocol {
     val accumulatedValues = {
       Utils.jsonOption(json \ "Accumulables").map(_.extract[List[JValue]]) match {
         case Some(values) => values.map(accumulableInfoFromJson)
-        case None => Seq[AccumulableInfo]()
+        case None => Seq.empty[AccumulableInfo]
       }
     }
 
@@ -726,7 +726,7 @@ private[spark] object JsonProtocol {
     val killed = Utils.jsonOption(json \ "Killed").exists(_.extract[Boolean])
     val accumulables = Utils.jsonOption(json \ "Accumulables").map(_.extract[Seq[JValue]]) match {
       case Some(values) => values.map(accumulableInfoFromJson)
-      case None => Seq[AccumulableInfo]()
+      case None => Seq.empty[AccumulableInfo]
     }
 
     val taskInfo =
diff --git a/core/src/main/scala/org/apache/spark/util/Utils.scala b/core/src/main/scala/org/apache/spark/util/Utils.scala
index 584337a71c..d661293e52 100644
--- a/core/src/main/scala/org/apache/spark/util/Utils.scala
+++ b/core/src/main/scala/org/apache/spark/util/Utils.scala
@@ -1443,7 +1443,7 @@ private[spark] object Utils extends Logging {
     var firstUserFile = "<unknown>"
     var firstUserLine = 0
     var insideSpark = true
-    var callStack = new ArrayBuffer[String]() :+ "<unknown>"
+    val callStack = new ArrayBuffer[String]() :+ "<unknown>"
 
     Thread.currentThread.getStackTrace().foreach { ste: StackTraceElement =>
       // When running under some profilers, the current stack trace might contain some bogus
@@ -2438,7 +2438,7 @@ private[spark] object Utils extends Logging {
       .getOrElse(UserGroupInformation.getCurrentUser().getShortUserName())
   }
 
-  val EMPTY_USER_GROUPS = Set[String]()
+  val EMPTY_USER_GROUPS = Set.empty[String]
 
   // Returns the groups to which the current user belongs.
   def getCurrentUserGroups(sparkConf: SparkConf, username: String): Set[String] = {
@@ -2587,7 +2587,7 @@ private[spark] object Utils extends Logging {
    * Unions two comma-separated lists of files and filters out empty strings.
    */
   def unionFileLists(leftList: Option[String], rightList: Option[String]): Set[String] = {
-    var allFiles = Set[String]()
+    var allFiles = Set.empty[String]
     leftList.foreach { value => allFiles ++= value.split(",") }
     rightList.foreach { value => allFiles ++= value.split(",") }
     allFiles.filter { _.nonEmpty }
diff --git a/examples/src/main/scala/org/apache/spark/examples/LocalFileLR.scala b/examples/src/main/scala/org/apache/spark/examples/LocalFileLR.scala
index a897cad02f..8dbb7ee4e5 100644
--- a/examples/src/main/scala/org/apache/spark/examples/LocalFileLR.scala
+++ b/examples/src/main/scala/org/apache/spark/examples/LocalFileLR.scala
@@ -53,16 +53,16 @@ object LocalFileLR {
 
     val fileSrc = scala.io.Source.fromFile(args(0))
     val lines = fileSrc.getLines().toArray
-    val points = lines.map(parsePoint _)
+    val points = lines.map(parsePoint)
     val ITERATIONS = args(1).toInt
 
     // Initialize w to a random value
-    var w = DenseVector.fill(D) {2 * rand.nextDouble - 1}
+    val w = DenseVector.fill(D) {2 * rand.nextDouble - 1}
     println("Initial w: " + w)
 
     for (i <- 1 to ITERATIONS) {
       println("On iteration " + i)
-      var gradient = DenseVector.zeros[Double](D)
+      val gradient = DenseVector.zeros[Double](D)
       for (p <- points) {
         val scale = (1 / (1 + math.exp(-p.y * (w.dot(p.x)))) - 1) * p.y
         gradient += p.x * scale
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 fca585c2a3..963c9a56d6 100644
--- a/examples/src/main/scala/org/apache/spark/examples/LocalKMeans.scala
+++ b/examples/src/main/scala/org/apache/spark/examples/LocalKMeans.scala
@@ -47,12 +47,11 @@ object LocalKMeans {
   }
 
   def closestPoint(p: Vector[Double], centers: HashMap[Int, Vector[Double]]): Int = {
-    var index = 0
     var bestIndex = 0
     var closest = Double.PositiveInfinity
 
     for (i <- 1 to centers.size) {
-      val vCurr = centers.get(i).get
+      val vCurr = centers(i)
       val tempDist = squaredDistance(p, vCurr)
       if (tempDist < closest) {
         closest = tempDist
@@ -76,8 +75,8 @@ object LocalKMeans {
     showWarning()
 
     val data = generateData
-    var points = new HashSet[Vector[Double]]
-    var kPoints = new HashMap[Int, Vector[Double]]
+    val points = new HashSet[Vector[Double]]
+    val kPoints = new HashMap[Int, Vector[Double]]
     var tempDist = 1.0
 
     while (points.size < K) {
@@ -92,11 +91,11 @@ object LocalKMeans {
     println("Initial centers: " + kPoints)
 
     while(tempDist > convergeDist) {
-      var closest = data.map (p => (closestPoint(p, kPoints), (p, 1)))
+      val closest = data.map (p => (closestPoint(p, kPoints), (p, 1)))
 
-      var mappings = closest.groupBy[Int] (x => x._1)
+      val mappings = closest.groupBy[Int] (x => x._1)
 
-      var pointStats = mappings.map { pair =>
+      val pointStats = mappings.map { pair =>
         pair._2.reduceLeft [(Int, (Vector[Double], Int))] {
           case ((id1, (p1, c1)), (id2, (p2, c2))) => (id1, (p1 + p2, c1 + c2))
         }
@@ -107,7 +106,7 @@ object LocalKMeans {
 
       tempDist = 0.0
       for (mapping <- newPoints) {
-        tempDist += squaredDistance(kPoints.get(mapping._1).get, mapping._2)
+        tempDist += squaredDistance(kPoints(mapping._1), mapping._2)
       }
 
       for (newP <- newPoints) {
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 13ccc2ae7c..eb5221f085 100644
--- a/examples/src/main/scala/org/apache/spark/examples/LocalLR.scala
+++ b/examples/src/main/scala/org/apache/spark/examples/LocalLR.scala
@@ -60,12 +60,12 @@ object LocalLR {
 
     val data = generateData
     // Initialize w to a random value
-    var w = DenseVector.fill(D) {2 * rand.nextDouble - 1}
+    val w = DenseVector.fill(D) {2 * rand.nextDouble - 1}
     println("Initial w: " + w)
 
     for (i <- 1 to ITERATIONS) {
       println("On iteration " + i)
-      var gradient = DenseVector.zeros[Double](D)
+      val gradient = DenseVector.zeros[Double](D)
       for (p <- data) {
         val scale = (1 / (1 + math.exp(-p.y * (w.dot(p.x)))) - 1) * p.y
         gradient +=  p.x * scale
diff --git a/examples/src/main/scala/org/apache/spark/examples/SparkHdfsLR.scala b/examples/src/main/scala/org/apache/spark/examples/SparkHdfsLR.scala
index 05ac6cbcb3..9d675bbc18 100644
--- a/examples/src/main/scala/org/apache/spark/examples/SparkHdfsLR.scala
+++ b/examples/src/main/scala/org/apache/spark/examples/SparkHdfsLR.scala
@@ -40,8 +40,8 @@ object SparkHdfsLR {
 
   def parsePoint(line: String): DataPoint = {
     val tok = new java.util.StringTokenizer(line, " ")
-    var y = tok.nextToken.toDouble
-    var x = new Array[Double](D)
+    val y = tok.nextToken.toDouble
+    val x = new Array[Double](D)
     var i = 0
     while (i < D) {
       x(i) = tok.nextToken.toDouble; i += 1
@@ -78,7 +78,7 @@ object SparkHdfsLR {
     val ITERATIONS = args(1).toInt
 
     // Initialize w to a random value
-    var w = DenseVector.fill(D) {2 * rand.nextDouble - 1}
+    val w = DenseVector.fill(D) {2 * rand.nextDouble - 1}
     println("Initial w: " + w)
 
     for (i <- 1 to ITERATIONS) {
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 cb2be091ff..c18e3d31f1 100644
--- a/examples/src/main/scala/org/apache/spark/examples/SparkLR.scala
+++ b/examples/src/main/scala/org/apache/spark/examples/SparkLR.scala
@@ -72,7 +72,7 @@ object SparkLR {
     val points = spark.sparkContext.parallelize(generateData, numSlices).cache()
 
     // Initialize w to a random value
-    var w = DenseVector.fill(D) {2 * rand.nextDouble - 1}
+    val w = DenseVector.fill(D) {2 * rand.nextDouble - 1}
     println("Initial w: " + w)
 
     for (i <- 1 to ITERATIONS) {
diff --git a/examples/src/main/scala/org/apache/spark/examples/ml/DecisionTreeExample.scala b/examples/src/main/scala/org/apache/spark/examples/ml/DecisionTreeExample.scala
index b03701e491..19f2d7751b 100644
--- a/examples/src/main/scala/org/apache/spark/examples/ml/DecisionTreeExample.scala
+++ b/examples/src/main/scala/org/apache/spark/examples/ml/DecisionTreeExample.scala
@@ -251,7 +251,7 @@ object DecisionTreeExample {
           .setMinInfoGain(params.minInfoGain)
           .setCacheNodeIds(params.cacheNodeIds)
           .setCheckpointInterval(params.checkpointInterval)
-      case _ => throw new IllegalArgumentException("Algo ${params.algo} not supported.")
+      case _ => throw new IllegalArgumentException(s"Algo ${params.algo} not supported.")
     }
     stages += dt
     val pipeline = new Pipeline().setStages(stages.toArray)
@@ -278,7 +278,7 @@ object DecisionTreeExample {
         } else {
           println(treeModel) // Print model summary.
         }
-      case _ => throw new IllegalArgumentException("Algo ${params.algo} not supported.")
+      case _ => throw new IllegalArgumentException(s"Algo ${params.algo} not supported.")
     }
 
     // Evaluate model on training, test data.
@@ -294,7 +294,7 @@ object DecisionTreeExample {
         println("Test data results:")
         evaluateRegressionModel(pipelineModel, test, labelColName)
       case _ =>
-        throw new IllegalArgumentException("Algo ${params.algo} not supported.")
+        throw new IllegalArgumentException(s"Algo ${params.algo} not supported.")
     }
 
     spark.stop()
diff --git a/examples/src/main/scala/org/apache/spark/examples/ml/GBTExample.scala b/examples/src/main/scala/org/apache/spark/examples/ml/GBTExample.scala
index 3bd8ff54c2..8f3ce4b315 100644
--- a/examples/src/main/scala/org/apache/spark/examples/ml/GBTExample.scala
+++ b/examples/src/main/scala/org/apache/spark/examples/ml/GBTExample.scala
@@ -190,7 +190,7 @@ object GBTExample {
           .setCacheNodeIds(params.cacheNodeIds)
           .setCheckpointInterval(params.checkpointInterval)
           .setMaxIter(params.maxIter)
-      case _ => throw new IllegalArgumentException("Algo ${params.algo} not supported.")
+      case _ => throw new IllegalArgumentException(s"Algo ${params.algo} not supported.")
     }
     stages += dt
     val pipeline = new Pipeline().setStages(stages.toArray)
@@ -217,7 +217,7 @@ object GBTExample {
         } else {
           println(rfModel) // Print model summary.
         }
-      case _ => throw new IllegalArgumentException("Algo ${params.algo} not supported.")
+      case _ => throw new IllegalArgumentException(s"Algo ${params.algo} not supported.")
     }
 
     // Evaluate model on training, test data.
@@ -233,7 +233,7 @@ object GBTExample {
         println("Test data results:")
         DecisionTreeExample.evaluateRegressionModel(pipelineModel, test, labelColName)
       case _ =>
-        throw new IllegalArgumentException("Algo ${params.algo} not supported.")
+        throw new IllegalArgumentException(s"Algo ${params.algo} not supported.")
     }
 
     spark.stop()
diff --git a/examples/src/main/scala/org/apache/spark/examples/ml/RandomForestExample.scala b/examples/src/main/scala/org/apache/spark/examples/ml/RandomForestExample.scala
index a735c218c0..3c127a46e1 100644
--- a/examples/src/main/scala/org/apache/spark/examples/ml/RandomForestExample.scala
+++ b/examples/src/main/scala/org/apache/spark/examples/ml/RandomForestExample.scala
@@ -198,7 +198,7 @@ object RandomForestExample {
           .setCheckpointInterval(params.checkpointInterval)
           .setFeatureSubsetStrategy(params.featureSubsetStrategy)
           .setNumTrees(params.numTrees)
-      case _ => throw new IllegalArgumentException("Algo ${params.algo} not supported.")
+      case _ => throw new IllegalArgumentException(s"Algo ${params.algo} not supported.")
     }
     stages += dt
     val pipeline = new Pipeline().setStages(stages.toArray)
@@ -225,7 +225,7 @@ object RandomForestExample {
         } else {
           println(rfModel) // Print model summary.
         }
-      case _ => throw new IllegalArgumentException("Algo ${params.algo} not supported.")
+      case _ => throw new IllegalArgumentException(s"Algo ${params.algo} not supported.")
     }
 
     // Evaluate model on training, test data.
@@ -241,7 +241,7 @@ object RandomForestExample {
         println("Test data results:")
         DecisionTreeExample.evaluateRegressionModel(pipelineModel, test, labelColName)
       case _ =>
-        throw new IllegalArgumentException("Algo ${params.algo} not supported.")
+        throw new IllegalArgumentException(s"Algo ${params.algo} not supported.")
     }
 
     spark.stop()
diff --git a/examples/src/main/scala/org/apache/spark/examples/mllib/DecisionTreeRunner.scala b/examples/src/main/scala/org/apache/spark/examples/mllib/DecisionTreeRunner.scala
index 0ad0465a02..fa47e12857 100644
--- a/examples/src/main/scala/org/apache/spark/examples/mllib/DecisionTreeRunner.scala
+++ b/examples/src/main/scala/org/apache/spark/examples/mllib/DecisionTreeRunner.scala
@@ -211,7 +211,7 @@ object DecisionTreeRunner {
       case Regression =>
         (origExamples, null, 0)
       case _ =>
-        throw new IllegalArgumentException("Algo ${params.algo} not supported.")
+        throw new IllegalArgumentException(s"Algo $algo not supported.")
     }
 
     // Create training, test sets.
diff --git a/external/kafka-0-10-sql/src/test/scala/org/apache/spark/sql/kafka010/KafkaTestUtils.scala b/external/kafka-0-10-sql/src/test/scala/org/apache/spark/sql/kafka010/KafkaTestUtils.scala
index f86b8f586d..5915d9f99a 100644
--- a/external/kafka-0-10-sql/src/test/scala/org/apache/spark/sql/kafka010/KafkaTestUtils.scala
+++ b/external/kafka-0-10-sql/src/test/scala/org/apache/spark/sql/kafka010/KafkaTestUtils.scala
@@ -378,7 +378,7 @@ class KafkaTestUtils(withBrokerProps: Map[String, Object] = Map.empty) extends L
 
         zkUtils.getLeaderForPartition(topic, partition).isDefined &&
           Request.isValidBrokerId(leaderAndInSyncReplicas.leader) &&
-          leaderAndInSyncReplicas.isr.size >= 1
+          leaderAndInSyncReplicas.isr.nonEmpty
 
       case _ =>
         false
diff --git a/external/kafka-0-10/src/main/scala/org/apache/spark/streaming/kafka010/KafkaRDD.scala b/external/kafka-0-10/src/main/scala/org/apache/spark/streaming/kafka010/KafkaRDD.scala
index 62cdf5b113..d9fc9cc206 100644
--- a/external/kafka-0-10/src/main/scala/org/apache/spark/streaming/kafka010/KafkaRDD.scala
+++ b/external/kafka-0-10/src/main/scala/org/apache/spark/streaming/kafka010/KafkaRDD.scala
@@ -156,7 +156,7 @@ private[spark] class KafkaRDD[K, V](
     val prefExecs = if (null == prefHost) allExecs else allExecs.filter(_.host == prefHost)
     val execs = if (prefExecs.isEmpty) allExecs else prefExecs
     if (execs.isEmpty) {
-      Seq()
+      Seq.empty
     } else {
       // execs is sorted, tp.hashCode depends only on topic and partition, so consistent index
       val index = Math.floorMod(tp.hashCode, execs.length)
diff --git a/external/kafka-0-10/src/main/scala/org/apache/spark/streaming/kafka010/KafkaTestUtils.scala b/external/kafka-0-10/src/main/scala/org/apache/spark/streaming/kafka010/KafkaTestUtils.scala
index 8273c2b49f..6c7024ea4b 100644
--- a/external/kafka-0-10/src/main/scala/org/apache/spark/streaming/kafka010/KafkaTestUtils.scala
+++ b/external/kafka-0-10/src/main/scala/org/apache/spark/streaming/kafka010/KafkaTestUtils.scala
@@ -257,7 +257,7 @@ private[kafka010] class KafkaTestUtils extends Logging {
 
         zkUtils.getLeaderForPartition(topic, partition).isDefined &&
           Request.isValidBrokerId(leaderAndInSyncReplicas.leader) &&
-          leaderAndInSyncReplicas.isr.size >= 1
+          leaderAndInSyncReplicas.isr.nonEmpty
 
       case _ =>
         false
diff --git a/graphx/src/main/scala/org/apache/spark/graphx/impl/EdgePartition.scala b/graphx/src/main/scala/org/apache/spark/graphx/impl/EdgePartition.scala
index 26349f4d88..0e6a340a68 100644
--- a/graphx/src/main/scala/org/apache/spark/graphx/impl/EdgePartition.scala
+++ b/graphx/src/main/scala/org/apache/spark/graphx/impl/EdgePartition.scala
@@ -388,7 +388,7 @@ class EdgePartition[
     val aggregates = new Array[A](vertexAttrs.length)
     val bitset = new BitSet(vertexAttrs.length)
 
-    var ctx = new AggregatingEdgeContext[VD, ED, A](mergeMsg, aggregates, bitset)
+    val ctx = new AggregatingEdgeContext[VD, ED, A](mergeMsg, aggregates, bitset)
     var i = 0
     while (i < size) {
       val localSrcId = localSrcIds(i)
@@ -433,7 +433,7 @@ class EdgePartition[
     val aggregates = new Array[A](vertexAttrs.length)
     val bitset = new BitSet(vertexAttrs.length)
 
-    var ctx = new AggregatingEdgeContext[VD, ED, A](mergeMsg, aggregates, bitset)
+    val ctx = new AggregatingEdgeContext[VD, ED, A](mergeMsg, aggregates, bitset)
     index.iterator.foreach { cluster =>
       val clusterSrcId = cluster._1
       val clusterPos = cluster._2
diff --git a/graphx/src/main/scala/org/apache/spark/graphx/impl/GraphImpl.scala b/graphx/src/main/scala/org/apache/spark/graphx/impl/GraphImpl.scala
index 5d2a53782b..34e1253ff4 100644
--- a/graphx/src/main/scala/org/apache/spark/graphx/impl/GraphImpl.scala
+++ b/graphx/src/main/scala/org/apache/spark/graphx/impl/GraphImpl.scala
@@ -74,7 +74,7 @@ class GraphImpl[VD: ClassTag, ED: ClassTag] protected (
   override def getCheckpointFiles: Seq[String] = {
     Seq(vertices.getCheckpointFile, replicatedVertexView.edges.getCheckpointFile).flatMap {
       case Some(path) => Seq(path)
-      case None => Seq()
+      case None => Seq.empty
     }
   }
 
diff --git a/graphx/src/main/scala/org/apache/spark/graphx/util/GraphGenerators.scala b/graphx/src/main/scala/org/apache/spark/graphx/util/GraphGenerators.scala
index 2b3e5f98c4..419731146d 100644
--- a/graphx/src/main/scala/org/apache/spark/graphx/util/GraphGenerators.scala
+++ b/graphx/src/main/scala/org/apache/spark/graphx/util/GraphGenerators.scala
@@ -18,6 +18,7 @@
 package org.apache.spark.graphx.util
 
 import scala.annotation.tailrec
+import scala.collection.mutable
 import scala.reflect.ClassTag
 import scala.util._
 
@@ -133,7 +134,7 @@ object GraphGenerators extends Logging {
       throw new IllegalArgumentException(
         s"numEdges must be <= $numEdgesUpperBound but was $numEdges")
     }
-    var edges: Set[Edge[Int]] = Set()
+    var edges = mutable.Set.empty[Edge[Int]]
     while (edges.size < numEdges) {
       if (edges.size % 100 == 0) {
         logDebug(edges.size + " edges")
diff --git a/mllib/src/main/scala/org/apache/spark/ml/classification/LogisticRegression.scala b/mllib/src/main/scala/org/apache/spark/ml/classification/LogisticRegression.scala
index b234bc4c2d..65b09e5712 100644
--- a/mllib/src/main/scala/org/apache/spark/ml/classification/LogisticRegression.scala
+++ b/mllib/src/main/scala/org/apache/spark/ml/classification/LogisticRegression.scala
@@ -736,7 +736,7 @@ class LogisticRegression @Since("1.2.0") (
                b_k' = b_k - \mean(b_k)
              }}}
            */
-          val rawIntercepts = histogram.map(c => math.log(c + 1)) // add 1 for smoothing
+          val rawIntercepts = histogram.map(math.log1p) // add 1 for smoothing (log1p(x) = log(1+x))
           val rawMean = rawIntercepts.sum / rawIntercepts.length
           rawIntercepts.indices.foreach { i =>
             initialCoefWithInterceptMatrix.update(i, numFeatures, rawIntercepts(i) - rawMean)
@@ -820,7 +820,7 @@ class LogisticRegression @Since("1.2.0") (
         val interceptVec = if ($(fitIntercept) || !isMultinomial) {
           Vectors.zeros(numCoefficientSets)
         } else {
-          Vectors.sparse(numCoefficientSets, Seq())
+          Vectors.sparse(numCoefficientSets, Seq.empty)
         }
         // separate intercepts and coefficients from the combined matrix
         allCoefMatrix.foreachActive { (classIndex, featureIndex, value) =>
diff --git a/mllib/src/main/scala/org/apache/spark/ml/feature/RFormulaParser.scala b/mllib/src/main/scala/org/apache/spark/ml/feature/RFormulaParser.scala
index 2dd565a782..32835fb3aa 100644
--- a/mllib/src/main/scala/org/apache/spark/ml/feature/RFormulaParser.scala
+++ b/mllib/src/main/scala/org/apache/spark/ml/feature/RFormulaParser.scala
@@ -99,7 +99,7 @@ private[ml] case class ParsedRFormula(label: ColumnRef, terms: Seq[Term]) {
     }).map(_.distinct)
 
     // Deduplicates feature interactions, for example, a:b is the same as b:a.
-    var seen = mutable.Set[Set[String]]()
+    val seen = mutable.Set[Set[String]]()
     validInteractions.flatMap {
       case t if seen.contains(t.toSet) =>
         None
diff --git a/mllib/src/main/scala/org/apache/spark/ml/regression/LinearRegression.scala b/mllib/src/main/scala/org/apache/spark/ml/regression/LinearRegression.scala
index 91cd229704..ccc61feee8 100644
--- a/mllib/src/main/scala/org/apache/spark/ml/regression/LinearRegression.scala
+++ b/mllib/src/main/scala/org/apache/spark/ml/regression/LinearRegression.scala
@@ -286,7 +286,7 @@ class LinearRegression @Since("1.3.0") (@Since("1.3.0") override val uid: String
             s"training is not needed.")
         }
         if (handlePersistence) instances.unpersist()
-        val coefficients = Vectors.sparse(numFeatures, Seq())
+        val coefficients = Vectors.sparse(numFeatures, Seq.empty)
         val intercept = yMean
 
         val model = copyValues(new LinearRegressionModel(uid, coefficients, intercept))
diff --git a/mllib/src/main/scala/org/apache/spark/mllib/clustering/KMeans.scala b/mllib/src/main/scala/org/apache/spark/mllib/clustering/KMeans.scala
index 98e50c5b45..49043b5acb 100644
--- a/mllib/src/main/scala/org/apache/spark/mllib/clustering/KMeans.scala
+++ b/mllib/src/main/scala/org/apache/spark/mllib/clustering/KMeans.scala
@@ -363,7 +363,7 @@ class KMeans private (
     // to their squared distance from the centers. Note that only distances between points
     // and new centers are computed in each iteration.
     var step = 0
-    var bcNewCentersList = ArrayBuffer[Broadcast[_]]()
+    val bcNewCentersList = ArrayBuffer[Broadcast[_]]()
     while (step < initializationSteps) {
       val bcNewCenters = data.context.broadcast(newCenters)
       bcNewCentersList += bcNewCenters
diff --git a/mllib/src/main/scala/org/apache/spark/mllib/linalg/EigenValueDecomposition.scala b/mllib/src/main/scala/org/apache/spark/mllib/linalg/EigenValueDecomposition.scala
index 7695aabf43..c7c1a5404e 100644
--- a/mllib/src/main/scala/org/apache/spark/mllib/linalg/EigenValueDecomposition.scala
+++ b/mllib/src/main/scala/org/apache/spark/mllib/linalg/EigenValueDecomposition.scala
@@ -78,13 +78,13 @@ private[mllib] object EigenValueDecomposition {
     require(n * ncv.toLong <= Integer.MAX_VALUE && ncv * (ncv.toLong + 8) <= Integer.MAX_VALUE,
       s"k = $k and/or n = $n are too large to compute an eigendecomposition")
 
-    var ido = new intW(0)
-    var info = new intW(0)
-    var resid = new Array[Double](n)
-    var v = new Array[Double](n * ncv)
-    var workd = new Array[Double](n * 3)
-    var workl = new Array[Double](ncv * (ncv + 8))
-    var ipntr = new Array[Int](11)
+    val ido = new intW(0)
+    val info = new intW(0)
+    val resid = new Array[Double](n)
+    val v = new Array[Double](n * ncv)
+    val workd = new Array[Double](n * 3)
+    val workl = new Array[Double](ncv * (ncv + 8))
+    val ipntr = new Array[Int](11)
 
     // call ARPACK's reverse communication, first iteration with ido = 0
     arpack.dsaupd(ido, bmat, n, which, nev.`val`, tolW, resid, ncv, v, n, iparam, ipntr, workd,
diff --git a/mllib/src/main/scala/org/apache/spark/mllib/optimization/LBFGS.scala b/mllib/src/main/scala/org/apache/spark/mllib/optimization/LBFGS.scala
index efedebe301..21ec287e49 100644
--- a/mllib/src/main/scala/org/apache/spark/mllib/optimization/LBFGS.scala
+++ b/mllib/src/main/scala/org/apache/spark/mllib/optimization/LBFGS.scala
@@ -257,7 +257,7 @@ object LBFGS extends Logging {
           (denseGrad1, loss1 + loss2)
        }
 
-      val zeroSparseVector = Vectors.sparse(n, Seq())
+      val zeroSparseVector = Vectors.sparse(n, Seq.empty)
       val (gradientSum, lossSum) = data.treeAggregate((zeroSparseVector, 0.0))(seqOp, combOp)
 
       // broadcasted model is not needed anymore
diff --git a/mllib/src/main/scala/org/apache/spark/mllib/stat/correlation/SpearmanCorrelation.scala b/mllib/src/main/scala/org/apache/spark/mllib/stat/correlation/SpearmanCorrelation.scala
index b760347bcb..ee51d33239 100644
--- a/mllib/src/main/scala/org/apache/spark/mllib/stat/correlation/SpearmanCorrelation.scala
+++ b/mllib/src/main/scala/org/apache/spark/mllib/stat/correlation/SpearmanCorrelation.scala
@@ -57,7 +57,7 @@ private[stat] object SpearmanCorrelation extends Correlation with Logging {
       var preCol = -1
       var preVal = Double.NaN
       var startRank = -1.0
-      var cachedUids = ArrayBuffer.empty[Long]
+      val cachedUids = ArrayBuffer.empty[Long]
       val flush: () => Iterable[(Long, (Int, Double))] = () => {
         val averageRank = startRank + (cachedUids.size - 1) / 2.0
         val output = cachedUids.map { uid =>
diff --git a/mllib/src/main/scala/org/apache/spark/mllib/stat/test/StreamingTest.scala b/mllib/src/main/scala/org/apache/spark/mllib/stat/test/StreamingTest.scala
index 551ea35795..80c6ef0ea1 100644
--- a/mllib/src/main/scala/org/apache/spark/mllib/stat/test/StreamingTest.scala
+++ b/mllib/src/main/scala/org/apache/spark/mllib/stat/test/StreamingTest.scala
@@ -133,7 +133,7 @@ class StreamingTest @Since("1.6.0") () extends Logging with Serializable {
       if (time.milliseconds > data.slideDuration.milliseconds * peacePeriod) {
         rdd
       } else {
-        data.context.sparkContext.parallelize(Seq())
+        data.context.sparkContext.parallelize(Seq.empty)
       }
     }
   }
diff --git a/project/SparkBuild.scala b/project/SparkBuild.scala
index 41f3a0451a..b9db1df2d1 100644
--- a/project/SparkBuild.scala
+++ b/project/SparkBuild.scala
@@ -589,7 +589,7 @@ object PySparkAssembly {
       val zipFile = new File(BuildCommons.sparkHome , "python/lib/pyspark.zip")
       zipFile.delete()
       zipRecursive(src, zipFile)
-      Seq[File]()
+      Seq.empty[File]
     }).value
   )
 
@@ -810,7 +810,7 @@ object TestSettings {
           require(d.mkdir() || d.isDirectory(), s"Failed to create directory $d")
         }
       }
-      Seq[File]()
+      Seq.empty[File]
     }).value,
     concurrentRestrictions in Global += Tags.limit(Tags.Test, 1),
     // Remove certain packages from Scaladoc
diff --git a/resource-managers/mesos/src/main/scala/org/apache/spark/deploy/mesos/ui/DriverPage.scala b/resource-managers/mesos/src/main/scala/org/apache/spark/deploy/mesos/ui/DriverPage.scala
index a6bb5d5915..022191d007 100644
--- a/resource-managers/mesos/src/main/scala/org/apache/spark/deploy/mesos/ui/DriverPage.scala
+++ b/resource-managers/mesos/src/main/scala/org/apache/spark/deploy/mesos/ui/DriverPage.scala
@@ -112,7 +112,7 @@ private[ui] class DriverPage(parent: MesosClusterUI) extends WebUIPage("driver")
         <td>Last Task Status</td>
         <td>{state.mesosTaskStatus.map(_.toString).getOrElse("")}</td>
       </tr>
-    }.getOrElse(Seq[Node]())
+    }.getOrElse(Seq.empty[Node])
   }
 
   private def propertiesRow(properties: collection.Map[String, String]): Seq[Node] = {
@@ -175,6 +175,6 @@ private[ui] class DriverPage(parent: MesosClusterUI) extends WebUIPage("driver")
           {state.retries}
         </td>
       </tr>
-    }.getOrElse(Seq[Node]())
+    }.getOrElse(Seq.empty[Node])
   }
 }
diff --git a/resource-managers/mesos/src/main/scala/org/apache/spark/scheduler/cluster/mesos/MesosSchedulerUtils.scala b/resource-managers/mesos/src/main/scala/org/apache/spark/scheduler/cluster/mesos/MesosSchedulerUtils.scala
index 062ed1f93f..7ec116c74b 100644
--- a/resource-managers/mesos/src/main/scala/org/apache/spark/scheduler/cluster/mesos/MesosSchedulerUtils.scala
+++ b/resource-managers/mesos/src/main/scala/org/apache/spark/scheduler/cluster/mesos/MesosSchedulerUtils.scala
@@ -333,7 +333,7 @@ trait MesosSchedulerUtils extends Logging {
       try {
         splitter.split(constraintsVal).asScala.toMap.mapValues(v =>
           if (v == null || v.isEmpty) {
-            Set[String]()
+            Set.empty[String]
           } else {
             v.split(',').toSet
           }
diff --git a/sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/analysis/Analyzer.scala b/sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/analysis/Analyzer.scala
index 7745709e07..501e7e3c69 100644
--- a/sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/analysis/Analyzer.scala
+++ b/sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/analysis/Analyzer.scala
@@ -2334,8 +2334,9 @@ object TimeWindowing extends Rule[LogicalPlan] {
       val windowExpressions =
         p.expressions.flatMap(_.collect { case t: TimeWindow => t }).toSet
 
+      val numWindowExpr = windowExpressions.size
       // Only support a single window expression for now
-      if (windowExpressions.size == 1 &&
+      if (numWindowExpr == 1 &&
           windowExpressions.head.timeColumn.resolved &&
           windowExpressions.head.checkInputDataTypes().isSuccess) {
 
@@ -2402,7 +2403,7 @@ object TimeWindowing extends Rule[LogicalPlan] {
 
           renamedPlan.withNewChildren(substitutedPlan :: Nil)
         }
-      } else if (windowExpressions.size > 1) {
+      } else if (numWindowExpr > 1) {
         p.failAnalysis("Multiple time window expressions would result in a cartesian product " +
           "of rows, therefore they are currently not supported.")
       } else {
diff --git a/sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/collectionOperations.scala b/sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/collectionOperations.scala
index c863ba4341..83a23cc97e 100644
--- a/sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/collectionOperations.scala
+++ b/sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/collectionOperations.scala
@@ -228,10 +228,10 @@ case class ArrayContains(left: Expression, right: Expression)
   override def dataType: DataType = BooleanType
 
   override def inputTypes: Seq[AbstractDataType] = right.dataType match {
-    case NullType => Seq()
+    case NullType => Seq.empty
     case _ => left.dataType match {
       case n @ ArrayType(element, _) => Seq(n, element)
-      case _ => Seq()
+      case _ => Seq.empty
     }
   }
 
diff --git a/sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/optimizer/CostBasedJoinReorder.scala b/sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/optimizer/CostBasedJoinReorder.scala
index db7baf6e9b..064ca68b7a 100644
--- a/sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/optimizer/CostBasedJoinReorder.scala
+++ b/sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/optimizer/CostBasedJoinReorder.scala
@@ -150,7 +150,7 @@ object JoinReorderDP extends PredicateHelper with Logging {
     // Create the initial plans: each plan is a single item with zero cost.
     val itemIndex = items.zipWithIndex
     val foundPlans = mutable.Buffer[JoinPlanMap](itemIndex.map {
-      case (item, id) => Set(id) -> JoinPlan(Set(id), item, Set(), Cost(0, 0))
+      case (item, id) => Set(id) -> JoinPlan(Set(id), item, Set.empty, Cost(0, 0))
     }.toMap)
 
     // Build filters from the join graph to be used by the search algorithm.
diff --git a/sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/optimizer/expressions.scala b/sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/optimizer/expressions.scala
index 6c83f47900..79a6c8663a 100644
--- a/sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/optimizer/expressions.scala
+++ b/sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/optimizer/expressions.scala
@@ -134,7 +134,7 @@ object ReorderAssociativeOperator extends Rule[LogicalPlan] {
   private def collectGroupingExpressions(plan: LogicalPlan): ExpressionSet = plan match {
     case Aggregate(groupingExpressions, aggregateExpressions, child) =>
       ExpressionSet.apply(groupingExpressions)
-    case _ => ExpressionSet(Seq())
+    case _ => ExpressionSet(Seq.empty)
   }
 
   def apply(plan: LogicalPlan): LogicalPlan = plan transform {
diff --git a/sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/parser/AstBuilder.scala b/sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/parser/AstBuilder.scala
index ad359e714b..45c1d3d430 100644
--- a/sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/parser/AstBuilder.scala
+++ b/sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/parser/AstBuilder.scala
@@ -877,7 +877,7 @@ class AstBuilder(conf: SQLConf) extends SqlBaseBaseVisitor[AnyRef] with Logging
 
     // Reverse the contexts to have them in the same sequence as in the SQL statement & turn them
     // into expressions.
-    val expressions = contexts.reverse.map(expression)
+    val expressions = contexts.reverseMap(expression)
 
     // Create a balanced tree.
     def reduceToExpressionTree(low: Int, high: Int): Expression = high - low match {
diff --git a/sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/planning/patterns.scala b/sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/planning/patterns.scala
index 7f370fb731..8d034c21a4 100644
--- a/sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/planning/patterns.scala
+++ b/sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/planning/patterns.scala
@@ -173,7 +173,7 @@ object ExtractFiltersAndInnerJoins extends PredicateHelper {
       val (plans, conditions) = flattenJoin(j)
       (plans, conditions ++ splitConjunctivePredicates(filterCondition))
 
-    case _ => (Seq((plan, parentJoinType)), Seq())
+    case _ => (Seq((plan, parentJoinType)), Seq.empty)
   }
 
   def unapply(plan: LogicalPlan): Option[(Seq[(LogicalPlan, InnerLike)], Seq[Expression])]
diff --git a/sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/plans/logical/statsEstimation/FilterEstimation.scala b/sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/plans/logical/statsEstimation/FilterEstimation.scala
index e13db85c7a..74820eb97d 100755
--- a/sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/plans/logical/statsEstimation/FilterEstimation.scala
+++ b/sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/plans/logical/statsEstimation/FilterEstimation.scala
@@ -47,7 +47,7 @@ case class FilterEstimation(plan: Filter) extends Logging {
 
     // Estimate selectivity of this filter predicate, and update column stats if needed.
     // For not-supported condition, set filter selectivity to a conservative estimate 100%
-    val filterSelectivity = calculateFilterSelectivity(plan.condition).getOrElse(BigDecimal(1.0))
+    val filterSelectivity = calculateFilterSelectivity(plan.condition).getOrElse(BigDecimal(1))
 
     val filteredRowCount: BigInt = ceil(BigDecimal(childStats.rowCount.get) * filterSelectivity)
     val newColStats = if (filteredRowCount == 0) {
@@ -83,13 +83,13 @@ case class FilterEstimation(plan: Filter) extends Logging {
     : Option[BigDecimal] = {
     condition match {
       case And(cond1, cond2) =>
-        val percent1 = calculateFilterSelectivity(cond1, update).getOrElse(BigDecimal(1.0))
-        val percent2 = calculateFilterSelectivity(cond2, update).getOrElse(BigDecimal(1.0))
+        val percent1 = calculateFilterSelectivity(cond1, update).getOrElse(BigDecimal(1))
+        val percent2 = calculateFilterSelectivity(cond2, update).getOrElse(BigDecimal(1))
         Some(percent1 * percent2)
 
       case Or(cond1, cond2) =>
-        val percent1 = calculateFilterSelectivity(cond1, update = false).getOrElse(BigDecimal(1.0))
-        val percent2 = calculateFilterSelectivity(cond2, update = false).getOrElse(BigDecimal(1.0))
+        val percent1 = calculateFilterSelectivity(cond1, update = false).getOrElse(BigDecimal(1))
+        val percent2 = calculateFilterSelectivity(cond2, update = false).getOrElse(BigDecimal(1))
         Some(percent1 + percent2 - (percent1 * percent2))
 
       // Not-operator pushdown
@@ -464,7 +464,7 @@ case class FilterEstimation(plan: Filter) extends Logging {
         (numericLiteral > max, numericLiteral <= min)
     }
 
-    var percent = BigDecimal(1.0)
+    var percent = BigDecimal(1)
     if (noOverlap) {
       percent = 0.0
     } else if (completeOverlap) {
@@ -630,7 +630,7 @@ case class FilterEstimation(plan: Filter) extends Logging {
         )
     }
 
-    var percent = BigDecimal(1.0)
+    var percent = BigDecimal(1)
     if (noOverlap) {
       percent = 0.0
     } else if (completeOverlap) {
diff --git a/sql/catalyst/src/test/scala/org/apache/spark/sql/catalyst/expressions/MathExpressionsSuite.scala b/sql/catalyst/src/test/scala/org/apache/spark/sql/catalyst/expressions/MathExpressionsSuite.scala
index f4d5a4471d..9ee777529a 100644
--- a/sql/catalyst/src/test/scala/org/apache/spark/sql/catalyst/expressions/MathExpressionsSuite.scala
+++ b/sql/catalyst/src/test/scala/org/apache/spark/sql/catalyst/expressions/MathExpressionsSuite.scala
@@ -609,9 +609,9 @@ class MathExpressionsSuite extends SparkFunSuite with ExpressionEvalHelper {
       checkEvaluation(BRound(floatPi, scale), floatResults(i), EmptyRow)
     }
 
-    val bdResults: Seq[BigDecimal] = Seq(BigDecimal(3.0), BigDecimal(3.1), BigDecimal(3.14),
-      BigDecimal(3.142), BigDecimal(3.1416), BigDecimal(3.14159),
-      BigDecimal(3.141593), BigDecimal(3.1415927))
+    val bdResults: Seq[BigDecimal] = Seq(BigDecimal(3), BigDecimal("3.1"), BigDecimal("3.14"),
+      BigDecimal("3.142"), BigDecimal("3.1416"), BigDecimal("3.14159"),
+      BigDecimal("3.141593"), BigDecimal("3.1415927"))
 
     (0 to 7).foreach { i =>
       checkEvaluation(Round(bdPi, i), bdResults(i), EmptyRow)
diff --git a/sql/catalyst/src/test/scala/org/apache/spark/sql/types/DecimalSuite.scala b/sql/catalyst/src/test/scala/org/apache/spark/sql/types/DecimalSuite.scala
index 144f3d688d..3193d1320a 100644
--- a/sql/catalyst/src/test/scala/org/apache/spark/sql/types/DecimalSuite.scala
+++ b/sql/catalyst/src/test/scala/org/apache/spark/sql/types/DecimalSuite.scala
@@ -109,8 +109,8 @@ class DecimalSuite extends SparkFunSuite with PrivateMethodTester {
 
   test("small decimals represented as unscaled long") {
     checkCompact(new Decimal(), true)
-    checkCompact(Decimal(BigDecimal(10.03)), false)
-    checkCompact(Decimal(BigDecimal(1e20)), false)
+    checkCompact(Decimal(BigDecimal("10.03")), false)
+    checkCompact(Decimal(BigDecimal("100000000000000000000")), false)
     checkCompact(Decimal(17L), true)
     checkCompact(Decimal(17), true)
     checkCompact(Decimal(17L, 2, 1), true)
diff --git a/sql/core/src/main/scala/org/apache/spark/sql/execution/command/ddl.scala b/sql/core/src/main/scala/org/apache/spark/sql/execution/command/ddl.scala
index ba7ca84f22..dae160f1bb 100644
--- a/sql/core/src/main/scala/org/apache/spark/sql/execution/command/ddl.scala
+++ b/sql/core/src/main/scala/org/apache/spark/sql/execution/command/ddl.scala
@@ -671,11 +671,11 @@ case class AlterTableRecoverPartitionsCommand(
         } else {
           logWarning(
             s"expected partition column ${partitionNames.head}, but got ${ps(0)}, ignoring it")
-          Seq()
+          Seq.empty
         }
       } else {
         logWarning(s"ignore ${new Path(path, name)}")
-        Seq()
+        Seq.empty
       }
     }
   }
diff --git a/sql/core/src/main/scala/org/apache/spark/sql/execution/datasources/jdbc/JDBCRelation.scala b/sql/core/src/main/scala/org/apache/spark/sql/execution/datasources/jdbc/JDBCRelation.scala
index a521fd1323..658d13768a 100644
--- a/sql/core/src/main/scala/org/apache/spark/sql/execution/datasources/jdbc/JDBCRelation.scala
+++ b/sql/core/src/main/scala/org/apache/spark/sql/execution/datasources/jdbc/JDBCRelation.scala
@@ -23,7 +23,6 @@ import org.apache.spark.internal.Logging
 import org.apache.spark.Partition
 import org.apache.spark.rdd.RDD
 import org.apache.spark.sql.{DataFrame, Row, SaveMode, SparkSession, SQLContext}
-import org.apache.spark.sql.execution.SQLExecution
 import org.apache.spark.sql.jdbc.JdbcDialects
 import org.apache.spark.sql.sources._
 import org.apache.spark.sql.types.StructType
@@ -81,7 +80,7 @@ private[sql] object JDBCRelation extends Logging {
     val column = partitioning.column
     var i: Int = 0
     var currentValue: Long = lowerBound
-    var ans = new ArrayBuffer[Partition]()
+    val ans = new ArrayBuffer[Partition]()
     while (i < numPartitions) {
       val lBound = if (i != 0) s"$column >= $currentValue" else null
       currentValue += stride
diff --git a/sql/core/src/main/scala/org/apache/spark/sql/execution/datasources/parquet/ParquetFileFormat.scala b/sql/core/src/main/scala/org/apache/spark/sql/execution/datasources/parquet/ParquetFileFormat.scala
index 87fbf8b1bc..64eea26a9f 100644
--- a/sql/core/src/main/scala/org/apache/spark/sql/execution/datasources/parquet/ParquetFileFormat.scala
+++ b/sql/core/src/main/scala/org/apache/spark/sql/execution/datasources/parquet/ParquetFileFormat.scala
@@ -220,7 +220,7 @@ class ParquetFileFormat
 
         val needMerged: Seq[FileStatus] =
           if (mergeRespectSummaries) {
-            Seq()
+            Seq.empty
           } else {
             filesByType.data
           }
diff --git a/sql/core/src/main/scala/org/apache/spark/sql/execution/objects.scala b/sql/core/src/main/scala/org/apache/spark/sql/execution/objects.scala
index 34391818f3..9e4e02b99b 100644
--- a/sql/core/src/main/scala/org/apache/spark/sql/execution/objects.scala
+++ b/sql/core/src/main/scala/org/apache/spark/sql/execution/objects.scala
@@ -35,8 +35,6 @@ import org.apache.spark.sql.catalyst.plans.logical.LogicalGroupState
 import org.apache.spark.sql.execution.streaming.GroupStateImpl
 import org.apache.spark.sql.streaming.GroupStateTimeout
 import org.apache.spark.sql.types._
-import org.apache.spark.util.Utils
-
 
 /**
  * Physical version of `ObjectProducer`.
@@ -403,8 +401,7 @@ case class FlatMapGroupsInRExec(
     Seq(groupingAttributes.map(SortOrder(_, Ascending)))
 
   override protected def doExecute(): RDD[InternalRow] = {
-    val isSerializedRData =
-      if (outputSchema == SERIALIZED_R_DATA_SCHEMA) true else false
+    val isSerializedRData = outputSchema == SERIALIZED_R_DATA_SCHEMA
     val serializerForR = if (!isSerializedRData) {
       SerializationFormats.ROW
     } else {
diff --git a/sql/core/src/main/scala/org/apache/spark/sql/execution/r/MapPartitionsRWrapper.scala b/sql/core/src/main/scala/org/apache/spark/sql/execution/r/MapPartitionsRWrapper.scala
index d2178e971e..b9835c7dbb 100644
--- a/sql/core/src/main/scala/org/apache/spark/sql/execution/r/MapPartitionsRWrapper.scala
+++ b/sql/core/src/main/scala/org/apache/spark/sql/execution/r/MapPartitionsRWrapper.scala
@@ -34,8 +34,7 @@ case class MapPartitionsRWrapper(
     outputSchema: StructType) extends (Iterator[Any] => Iterator[Any]) {
   def apply(iter: Iterator[Any]): Iterator[Any] = {
     // If the content of current DataFrame is serialized R data?
-    val isSerializedRData =
-      if (inputSchema == SERIALIZED_R_DATA_SCHEMA) true else false
+    val isSerializedRData = inputSchema == SERIALIZED_R_DATA_SCHEMA
 
     val (newIter, deserializer, colNames) =
       if (!isSerializedRData) {
diff --git a/sql/core/src/main/scala/org/apache/spark/sql/execution/streaming/CompactibleFileStreamLog.scala b/sql/core/src/main/scala/org/apache/spark/sql/execution/streaming/CompactibleFileStreamLog.scala
index 408c8f81f1..e37033b19a 100644
--- a/sql/core/src/main/scala/org/apache/spark/sql/execution/streaming/CompactibleFileStreamLog.scala
+++ b/sql/core/src/main/scala/org/apache/spark/sql/execution/streaming/CompactibleFileStreamLog.scala
@@ -170,12 +170,8 @@ abstract class CompactibleFileStreamLog[T <: AnyRef : ClassTag](
   private def compact(batchId: Long, logs: Array[T]): Boolean = {
     val validBatches = getValidBatchesBeforeCompactionBatch(batchId, compactInterval)
     val allLogs = validBatches.flatMap(batchId => super.get(batchId)).flatten ++ logs
-    if (super.add(batchId, compactLogs(allLogs).toArray)) {
-      true
-    } else {
-      // Return false as there is another writer.
-      false
-    }
+    // Return false as there is another writer.
+    super.add(batchId, compactLogs(allLogs).toArray)
   }
 
   /**
diff --git a/sql/core/src/main/scala/org/apache/spark/sql/execution/streaming/StreamExecution.scala b/sql/core/src/main/scala/org/apache/spark/sql/execution/streaming/StreamExecution.scala
index 5ee596e06d..5711262654 100644
--- a/sql/core/src/main/scala/org/apache/spark/sql/execution/streaming/StreamExecution.scala
+++ b/sql/core/src/main/scala/org/apache/spark/sql/execution/streaming/StreamExecution.scala
@@ -609,7 +609,7 @@ class StreamExecution(
     }
 
     // A list of attributes that will need to be updated.
-    var replacements = new ArrayBuffer[(Attribute, Attribute)]
+    val replacements = new ArrayBuffer[(Attribute, Attribute)]
     // Replace sources in the logical plan with data that has arrived since the last batch.
     val withNewSources = logicalPlan transform {
       case StreamingExecutionRelation(source, output) =>
diff --git a/sql/core/src/test/scala/org/apache/spark/sql/DataFrameAggregateSuite.scala b/sql/core/src/test/scala/org/apache/spark/sql/DataFrameAggregateSuite.scala
index 4568b67024..d802557b36 100644
--- a/sql/core/src/test/scala/org/apache/spark/sql/DataFrameAggregateSuite.scala
+++ b/sql/core/src/test/scala/org/apache/spark/sql/DataFrameAggregateSuite.scala
@@ -65,9 +65,9 @@ class DataFrameAggregateSuite extends QueryTest with SharedSQLContext {
 
     checkAnswer(
       decimalData.groupBy("a").agg(sum("b")),
-      Seq(Row(new java.math.BigDecimal(1.0), new java.math.BigDecimal(3.0)),
-        Row(new java.math.BigDecimal(2.0), new java.math.BigDecimal(3.0)),
-        Row(new java.math.BigDecimal(3.0), new java.math.BigDecimal(3.0)))
+      Seq(Row(new java.math.BigDecimal(1), new java.math.BigDecimal(3)),
+        Row(new java.math.BigDecimal(2), new java.math.BigDecimal(3)),
+        Row(new java.math.BigDecimal(3), new java.math.BigDecimal(3)))
     )
 
     val decimalDataWithNulls = spark.sparkContext.parallelize(
@@ -80,10 +80,10 @@ class DataFrameAggregateSuite extends QueryTest with SharedSQLContext {
       DecimalData(null, 2) :: Nil).toDF()
     checkAnswer(
       decimalDataWithNulls.groupBy("a").agg(sum("b")),
-      Seq(Row(new java.math.BigDecimal(1.0), new java.math.BigDecimal(1.0)),
-        Row(new java.math.BigDecimal(2.0), new java.math.BigDecimal(1.0)),
-        Row(new java.math.BigDecimal(3.0), new java.math.BigDecimal(3.0)),
-        Row(null, new java.math.BigDecimal(2.0)))
+      Seq(Row(new java.math.BigDecimal(1), new java.math.BigDecimal(1)),
+        Row(new java.math.BigDecimal(2), new java.math.BigDecimal(1)),
+        Row(new java.math.BigDecimal(3), new java.math.BigDecimal(3)),
+        Row(null, new java.math.BigDecimal(2)))
     )
   }
 
@@ -259,19 +259,19 @@ class DataFrameAggregateSuite extends QueryTest with SharedSQLContext {
 
     checkAnswer(
       decimalData.agg(avg('a)),
-      Row(new java.math.BigDecimal(2.0)))
+      Row(new java.math.BigDecimal(2)))
 
     checkAnswer(
       decimalData.agg(avg('a), sumDistinct('a)), // non-partial
-      Row(new java.math.BigDecimal(2.0), new java.math.BigDecimal(6)) :: Nil)
+      Row(new java.math.BigDecimal(2), new java.math.BigDecimal(6)) :: Nil)
 
     checkAnswer(
       decimalData.agg(avg('a cast DecimalType(10, 2))),
-      Row(new java.math.BigDecimal(2.0)))
+      Row(new java.math.BigDecimal(2)))
     // non-partial
     checkAnswer(
       decimalData.agg(avg('a cast DecimalType(10, 2)), sumDistinct('a cast DecimalType(10, 2))),
-      Row(new java.math.BigDecimal(2.0), new java.math.BigDecimal(6)) :: Nil)
+      Row(new java.math.BigDecimal(2), new java.math.BigDecimal(6)) :: Nil)
   }
 
   test("null average") {
@@ -520,9 +520,9 @@ class DataFrameAggregateSuite extends QueryTest with SharedSQLContext {
   test("SQL decimal test (used for catching certain decimal handling bugs in aggregates)") {
     checkAnswer(
       decimalData.groupBy('a cast DecimalType(10, 2)).agg(avg('b cast DecimalType(10, 2))),
-      Seq(Row(new java.math.BigDecimal(1.0), new java.math.BigDecimal(1.5)),
-        Row(new java.math.BigDecimal(2.0), new java.math.BigDecimal(1.5)),
-        Row(new java.math.BigDecimal(3.0), new java.math.BigDecimal(1.5))))
+      Seq(Row(new java.math.BigDecimal(1), new java.math.BigDecimal("1.5")),
+        Row(new java.math.BigDecimal(2), new java.math.BigDecimal("1.5")),
+        Row(new java.math.BigDecimal(3), new java.math.BigDecimal("1.5"))))
   }
 
   test("SPARK-17616: distinct aggregate combined with a non-partial aggregate") {
diff --git a/sql/core/src/test/scala/org/apache/spark/sql/DataFrameSuite.scala b/sql/core/src/test/scala/org/apache/spark/sql/DataFrameSuite.scala
index 3f3a6221d2..7c500728bd 100644
--- a/sql/core/src/test/scala/org/apache/spark/sql/DataFrameSuite.scala
+++ b/sql/core/src/test/scala/org/apache/spark/sql/DataFrameSuite.scala
@@ -1167,7 +1167,7 @@ class DataFrameSuite extends QueryTest with SharedSQLContext {
   }
 
   test("SPARK-6899: type should match when using codegen") {
-    checkAnswer(decimalData.agg(avg('a)), Row(new java.math.BigDecimal(2.0)))
+    checkAnswer(decimalData.agg(avg('a)), Row(new java.math.BigDecimal(2)))
   }
 
   test("SPARK-7133: Implement struct, array, and map field accessor") {
@@ -1971,7 +1971,7 @@ class DataFrameSuite extends QueryTest with SharedSQLContext {
 
   test("SPARK-19691 Calculating percentile of decimal column fails with ClassCastException") {
     val df = spark.range(1).selectExpr("CAST(id as DECIMAL) as x").selectExpr("percentile(x, 0.5)")
-    checkAnswer(df, Row(BigDecimal(0.0)) :: Nil)
+    checkAnswer(df, Row(BigDecimal(0)) :: Nil)
   }
 
   test("SPARK-19893: cannot run set operations with map type") {
diff --git a/sql/core/src/test/scala/org/apache/spark/sql/SQLQuerySuite.scala b/sql/core/src/test/scala/org/apache/spark/sql/SQLQuerySuite.scala
index c78ec6d9a8..e95f6dba46 100644
--- a/sql/core/src/test/scala/org/apache/spark/sql/SQLQuerySuite.scala
+++ b/sql/core/src/test/scala/org/apache/spark/sql/SQLQuerySuite.scala
@@ -1546,10 +1546,10 @@ class SQLQuerySuite extends QueryTest with SharedSQLContext {
       Seq(Row(d)))
     checkAnswer(
       df.selectExpr("b * a + b"),
-      Seq(Row(BigDecimal(2.12321))))
+      Seq(Row(BigDecimal("2.12321"))))
     checkAnswer(
       df.selectExpr("b * a - b"),
-      Seq(Row(BigDecimal(0.12321))))
+      Seq(Row(BigDecimal("0.12321"))))
     checkAnswer(
       df.selectExpr("b * a * b"),
       Seq(Row(d)))
diff --git a/sql/core/src/test/scala/org/apache/spark/sql/StringFunctionsSuite.scala b/sql/core/src/test/scala/org/apache/spark/sql/StringFunctionsSuite.scala
index bcc2351049..a12efc8356 100644
--- a/sql/core/src/test/scala/org/apache/spark/sql/StringFunctionsSuite.scala
+++ b/sql/core/src/test/scala/org/apache/spark/sql/StringFunctionsSuite.scala
@@ -387,7 +387,7 @@ class StringFunctionsSuite extends QueryTest with SharedSQLContext {
       Row("6.4817"))
 
     checkAnswer(
-      df.select(format_number(lit(BigDecimal(7.128381)), 4)), // not convert anything
+      df.select(format_number(lit(BigDecimal("7.128381")), 4)), // not convert anything
       Row("7.1284"))
 
     intercept[AnalysisException] {
diff --git a/sql/core/src/test/scala/org/apache/spark/sql/execution/datasources/json/JsonSuite.scala b/sql/core/src/test/scala/org/apache/spark/sql/execution/datasources/json/JsonSuite.scala
index 1cde137edb..80e5dd161d 100644
--- a/sql/core/src/test/scala/org/apache/spark/sql/execution/datasources/json/JsonSuite.scala
+++ b/sql/core/src/test/scala/org/apache/spark/sql/execution/datasources/json/JsonSuite.scala
@@ -826,7 +826,7 @@ class JsonSuite extends QueryTest with SharedSQLContext with TestJsonData {
       StructField("b", DecimalType(2, 2), true):: Nil)
 
     assert(expectedSchema === jsonDF.schema)
-    checkAnswer(jsonDF, Row(1.0E-39D, BigDecimal(0.01)))
+    checkAnswer(jsonDF, Row(1.0E-39D, BigDecimal("0.01")))
 
     val mergedJsonDF = spark.read
       .option("prefersDecimal", "true")
@@ -839,7 +839,7 @@ class JsonSuite extends QueryTest with SharedSQLContext with TestJsonData {
     assert(expectedMergedSchema === mergedJsonDF.schema)
     checkAnswer(
       mergedJsonDF,
-      Row(1.0E-39D, BigDecimal(0.01)) ::
+      Row(1.0E-39D, BigDecimal("0.01")) ::
       Row(1.0E38D, BigDecimal("92233720368547758070")) :: Nil
     )
   }
diff --git a/sql/core/src/test/scala/org/apache/spark/sql/execution/datasources/parquet/ParquetPartitionDiscoverySuite.scala b/sql/core/src/test/scala/org/apache/spark/sql/execution/datasources/parquet/ParquetPartitionDiscoverySuite.scala
index b4f3de9961..84b34d5ad2 100644
--- a/sql/core/src/test/scala/org/apache/spark/sql/execution/datasources/parquet/ParquetPartitionDiscoverySuite.scala
+++ b/sql/core/src/test/scala/org/apache/spark/sql/execution/datasources/parquet/ParquetPartitionDiscoverySuite.scala
@@ -676,7 +676,7 @@ class ParquetPartitionDiscoverySuite extends QueryTest with ParquetTest with Sha
         1.5.toFloat,
         4.5,
         new java.math.BigDecimal(new BigInteger("212500"), 5),
-        new java.math.BigDecimal(2.125),
+        new java.math.BigDecimal("2.125"),
         java.sql.Date.valueOf("2015-05-23"),
         new Timestamp(0),
         "This is a string, /[]?=:",
diff --git a/sql/hive/src/main/scala/org/apache/spark/sql/hive/HiveUtils.scala b/sql/hive/src/main/scala/org/apache/spark/sql/hive/HiveUtils.scala
index 2a522a1431..be6339f7dd 100644
--- a/sql/hive/src/main/scala/org/apache/spark/sql/hive/HiveUtils.scala
+++ b/sql/hive/src/main/scala/org/apache/spark/sql/hive/HiveUtils.scala
@@ -245,7 +245,7 @@ private[spark] object HiveUtils extends Logging {
     val loader = new IsolatedClientLoader(
       version = IsolatedClientLoader.hiveVersion(hiveExecutionVersion),
       sparkConf = conf,
-      execJars = Seq(),
+      execJars = Seq.empty,
       hadoopConf = hadoopConf,
       config = newTemporaryConfiguration(useInMemoryDerby = true),
       isolationOn = false,
diff --git a/sql/hive/src/main/scala/org/apache/spark/sql/hive/TableReader.scala b/sql/hive/src/main/scala/org/apache/spark/sql/hive/TableReader.scala
index 16c1103dd1..f238b9a4f7 100644
--- a/sql/hive/src/main/scala/org/apache/spark/sql/hive/TableReader.scala
+++ b/sql/hive/src/main/scala/org/apache/spark/sql/hive/TableReader.scala
@@ -162,8 +162,8 @@ class HadoopTableReader(
       if (!sparkSession.sessionState.conf.verifyPartitionPath) {
         partitionToDeserializer
       } else {
-        var existPathSet = collection.mutable.Set[String]()
-        var pathPatternSet = collection.mutable.Set[String]()
+        val existPathSet = collection.mutable.Set[String]()
+        val pathPatternSet = collection.mutable.Set[String]()
         partitionToDeserializer.filter {
           case (partition, partDeserializer) =>
             def updateExistPathSetByPathPattern(pathPatternStr: String) {
@@ -181,8 +181,8 @@ class HadoopTableReader(
             }
 
             val partPath = partition.getDataLocation
-            val partNum = Utilities.getPartitionDesc(partition).getPartSpec.size();
-            var pathPatternStr = getPathPatternByPath(partNum, partPath)
+            val partNum = Utilities.getPartitionDesc(partition).getPartSpec.size()
+            val pathPatternStr = getPathPatternByPath(partNum, partPath)
             if (!pathPatternSet.contains(pathPatternStr)) {
               pathPatternSet += pathPatternStr
               updateExistPathSetByPathPattern(pathPatternStr)
diff --git a/sql/hive/src/main/scala/org/apache/spark/sql/hive/client/HiveClientImpl.scala b/sql/hive/src/main/scala/org/apache/spark/sql/hive/client/HiveClientImpl.scala
index be024adac8..bde9a81c65 100644
--- a/sql/hive/src/main/scala/org/apache/spark/sql/hive/client/HiveClientImpl.scala
+++ b/sql/hive/src/main/scala/org/apache/spark/sql/hive/client/HiveClientImpl.scala
@@ -391,7 +391,7 @@ private[hive] class HiveClientImpl(
         val sortColumnNames = if (allAscendingSorted) {
           sortColumnOrders.map(_.getCol)
         } else {
-          Seq()
+          Seq.empty
         }
         Option(BucketSpec(h.getNumBuckets, h.getBucketCols.asScala, sortColumnNames))
       } else {
diff --git a/sql/hive/src/test/scala/org/apache/spark/sql/hive/HiveInspectorSuite.scala b/sql/hive/src/test/scala/org/apache/spark/sql/hive/HiveInspectorSuite.scala
index 3de1f4aeb7..11fd8c56e6 100644
--- a/sql/hive/src/test/scala/org/apache/spark/sql/hive/HiveInspectorSuite.scala
+++ b/sql/hive/src/test/scala/org/apache/spark/sql/hive/HiveInspectorSuite.scala
@@ -90,7 +90,7 @@ class HiveInspectorSuite extends SparkFunSuite with HiveInspectors {
     Literal(0.asInstanceOf[Double]) ::
     Literal("0") ::
     Literal(java.sql.Date.valueOf("2014-09-23")) ::
-    Literal(Decimal(BigDecimal(123.123))) ::
+    Literal(Decimal(BigDecimal("123.123"))) ::
     Literal(new java.sql.Timestamp(123123)) ::
     Literal(Array[Byte](1, 2, 3)) ::
     Literal.create(Seq[Int](1, 2, 3), ArrayType(IntegerType)) ::
diff --git a/sql/hive/src/test/scala/org/apache/spark/sql/hive/client/HiveClientSuite.scala b/sql/hive/src/test/scala/org/apache/spark/sql/hive/client/HiveClientSuite.scala
index 6a2c23a015..3eedcf7e08 100644
--- a/sql/hive/src/test/scala/org/apache/spark/sql/hive/client/HiveClientSuite.scala
+++ b/sql/hive/src/test/scala/org/apache/spark/sql/hive/client/HiveClientSuite.scala
@@ -21,12 +21,9 @@ import org.apache.hadoop.conf.Configuration
 import org.apache.hadoop.hive.conf.HiveConf
 import org.scalatest.BeforeAndAfterAll
 
-import org.apache.spark.SparkFunSuite
 import org.apache.spark.sql.catalyst.catalog._
-import org.apache.spark.sql.catalyst.expressions.{And, AttributeReference, EmptyRow, EqualTo, Expression, GreaterThan, GreaterThanOrEqual, In, InSet, LessThan, LessThanOrEqual, Like, Literal, Or}
+import org.apache.spark.sql.catalyst.expressions.{EmptyRow, Expression, In, InSet}
 import org.apache.spark.sql.catalyst.parser.CatalystSqlParser
-import org.apache.spark.sql.hive.HiveUtils
-import org.apache.spark.sql.types.{ByteType, IntegerType, StringType}
 
 // TODO: Refactor this to `HivePartitionFilteringSuite`
 class HiveClientSuite(version: String)
@@ -146,7 +143,7 @@ class HiveClientSuite(version: String)
       0 to 23,
       "aa" :: "ab" :: "ba" :: "bb" :: Nil, {
         case expr @ In(v, list) if expr.inSetConvertible =>
-          InSet(v, Set() ++ list.map(_.eval(EmptyRow)))
+          InSet(v, list.map(_.eval(EmptyRow)).toSet)
       })
   }
 
@@ -165,7 +162,7 @@ class HiveClientSuite(version: String)
       0 to 23,
       "ab" :: "ba" :: Nil, {
         case expr @ In(v, list) if expr.inSetConvertible =>
-          InSet(v, Set() ++ list.map(_.eval(EmptyRow)))
+          InSet(v, list.map(_.eval(EmptyRow)).toSet)
       })
   }
 
diff --git a/streaming/src/main/scala/org/apache/spark/streaming/StreamingContext.scala b/streaming/src/main/scala/org/apache/spark/streaming/StreamingContext.scala
index a34f6c73fe..f3b4ff2d1d 100644
--- a/streaming/src/main/scala/org/apache/spark/streaming/StreamingContext.scala
+++ b/streaming/src/main/scala/org/apache/spark/streaming/StreamingContext.scala
@@ -458,7 +458,7 @@ class StreamingContext private[streaming] (
       queue: Queue[RDD[T]],
       oneAtATime: Boolean = true
     ): InputDStream[T] = {
-    queueStream(queue, oneAtATime, sc.makeRDD(Seq[T](), 1))
+    queueStream(queue, oneAtATime, sc.makeRDD(Seq.empty[T], 1))
   }
 
   /**
diff --git a/streaming/src/main/scala/org/apache/spark/streaming/api/java/JavaDStreamLike.scala b/streaming/src/main/scala/org/apache/spark/streaming/api/java/JavaDStreamLike.scala
index a0a40fcee2..4a0ec31b5f 100644
--- a/streaming/src/main/scala/org/apache/spark/streaming/api/java/JavaDStreamLike.scala
+++ b/streaming/src/main/scala/org/apache/spark/streaming/api/java/JavaDStreamLike.scala
@@ -153,7 +153,7 @@ trait JavaDStreamLike[T, This <: JavaDStreamLike[T, This, R], R <: JavaRDDLike[T
   def context(): StreamingContext = dstream.context
 
   /** Return a new DStream by applying a function to all elements of this DStream. */
-  def map[R](f: JFunction[T, R]): JavaDStream[R] = {
+  def map[U](f: JFunction[T, U]): JavaDStream[U] = {
     new JavaDStream(dstream.map(f)(fakeClassTag))(fakeClassTag)
   }
 
diff --git a/streaming/src/main/scala/org/apache/spark/streaming/dstream/StateDStream.scala b/streaming/src/main/scala/org/apache/spark/streaming/dstream/StateDStream.scala
index 5bf1dabf08..d1a5e91793 100644
--- a/streaming/src/main/scala/org/apache/spark/streaming/dstream/StateDStream.scala
+++ b/streaming/src/main/scala/org/apache/spark/streaming/dstream/StateDStream.scala
@@ -76,7 +76,7 @@ class StateDStream[K: ClassTag, V: ClassTag, S: ClassTag](
             // Re-apply the update function to the old state RDD
             val updateFuncLocal = updateFunc
             val finalFunc = (iterator: Iterator[(K, S)]) => {
-              val i = iterator.map(t => (t._1, Seq[V](), Option(t._2)))
+              val i = iterator.map(t => (t._1, Seq.empty[V], Option(t._2)))
               updateFuncLocal(validTime, i)
             }
             val stateRDD = prevStateRDD.mapPartitions(finalFunc, preservePartitioning)
diff --git a/streaming/src/main/scala/org/apache/spark/streaming/util/RawTextHelper.scala b/streaming/src/main/scala/org/apache/spark/streaming/util/RawTextHelper.scala
index 408936653c..eb9996ece3 100644
--- a/streaming/src/main/scala/org/apache/spark/streaming/util/RawTextHelper.scala
+++ b/streaming/src/main/scala/org/apache/spark/streaming/util/RawTextHelper.scala
@@ -63,7 +63,6 @@ object RawTextHelper {
 
     var i = 0
     var len = 0
-    var done = false
     var value: (String, Long) = null
     var swap: (String, Long) = null
     var count = 0