diff --git a/core/src/main/scala/kafka/admin/TopicCommand.scala b/core/src/main/scala/kafka/admin/TopicCommand.scala
index c643a9df688d5..39bfe62ba4705 100755
--- a/core/src/main/scala/kafka/admin/TopicCommand.scala
+++ b/core/src/main/scala/kafka/admin/TopicCommand.scala
@@ -216,7 +216,7 @@ object TopicCommand extends Logging {
               val leader = zkUtils.getLeaderForPartition(topic, partitionId)
               if ((!reportUnderReplicatedPartitions && !reportUnavailablePartitions) ||
                   (reportUnderReplicatedPartitions && inSyncReplicas.size < assignedReplicas.size) ||
-                  (reportUnavailablePartitions && (!leader.isDefined || !liveBrokers.contains(leader.get)))) {
+                  (reportUnavailablePartitions && (leader.isEmpty || !liveBrokers.contains(leader.get)))) {
                 print("\tTopic: " + topic)
                 print("\tPartition: " + partitionId)
                 print("\tLeader: " + (if(leader.isDefined) leader.get else "none"))
diff --git a/core/src/main/scala/kafka/api/ApiVersion.scala b/core/src/main/scala/kafka/api/ApiVersion.scala
index 2417d795bc63c..666d0e79bba11 100644
--- a/core/src/main/scala/kafka/api/ApiVersion.scala
+++ b/core/src/main/scala/kafka/api/ApiVersion.scala
@@ -72,7 +72,7 @@ sealed trait ApiVersion extends Ordered[ApiVersion] {
   override def compare(that: ApiVersion): Int =
     ApiVersion.orderingByVersion.compare(this, that)
 
-  override def toString(): String = version
+  override def toString: String = version
 }
 
 // Keep the IDs in order of versions
diff --git a/core/src/main/scala/kafka/api/ControlledShutdownRequest.scala b/core/src/main/scala/kafka/api/ControlledShutdownRequest.scala
index 42a17e67fca33..52c8828810c49 100644
--- a/core/src/main/scala/kafka/api/ControlledShutdownRequest.scala
+++ b/core/src/main/scala/kafka/api/ControlledShutdownRequest.scala
@@ -63,7 +63,7 @@ case class ControlledShutdownRequest(versionId: Short,
       4 /* broker id */
   }
 
-  override def toString(): String = {
+  override def toString: String = {
     describe(true)
   }
 
diff --git a/core/src/main/scala/kafka/api/FetchRequest.scala b/core/src/main/scala/kafka/api/FetchRequest.scala
index 83e139a65e45f..f74bd1c983d3d 100644
--- a/core/src/main/scala/kafka/api/FetchRequest.scala
+++ b/core/src/main/scala/kafka/api/FetchRequest.scala
@@ -141,7 +141,7 @@ case class FetchRequest(versionId: Short = FetchRequest.CurrentVersion,
 
   def numPartitions = requestInfo.size
 
-  override def toString(): String = {
+  override def toString: String = {
     describe(true)
   }
 
diff --git a/core/src/main/scala/kafka/api/GenericRequestAndHeader.scala b/core/src/main/scala/kafka/api/GenericRequestAndHeader.scala
index b0c6d7a339850..cb5b95e52755f 100644
--- a/core/src/main/scala/kafka/api/GenericRequestAndHeader.scala
+++ b/core/src/main/scala/kafka/api/GenericRequestAndHeader.scala
@@ -39,7 +39,7 @@ private[kafka] abstract class GenericRequestAndHeader(val versionId: Short,
     body.sizeOf()
   }
 
-  override def toString(): String = {
+  override def toString: String = {
     describe(true)
   }
 
diff --git a/core/src/main/scala/kafka/api/GenericResponseAndHeader.scala b/core/src/main/scala/kafka/api/GenericResponseAndHeader.scala
index 748b5e935235f..2835fb6ea65e4 100644
--- a/core/src/main/scala/kafka/api/GenericResponseAndHeader.scala
+++ b/core/src/main/scala/kafka/api/GenericResponseAndHeader.scala
@@ -32,7 +32,7 @@ private[kafka] abstract class GenericResponseAndHeader(val correlationId: Int,
     body.sizeOf()
   }
 
-  override def toString(): String = {
+  override def toString: String = {
     describe(true)
   }
 
diff --git a/core/src/main/scala/kafka/api/LeaderAndIsr.scala b/core/src/main/scala/kafka/api/LeaderAndIsr.scala
index 5de527c50963b..e5813a535b7f1 100644
--- a/core/src/main/scala/kafka/api/LeaderAndIsr.scala
+++ b/core/src/main/scala/kafka/api/LeaderAndIsr.scala
@@ -35,7 +35,7 @@ object LeaderAndIsr {
 case class LeaderAndIsr(var leader: Int, var leaderEpoch: Int, var isr: List[Int], var zkVersion: Int) {
   def this(leader: Int, isr: List[Int]) = this(leader, LeaderAndIsr.initialLeaderEpoch, isr, LeaderAndIsr.initialZKVersion)
 
-  override def toString(): String = {
+  override def toString: String = {
     Json.encode(Map("leader" -> leader, "leader_epoch" -> leaderEpoch, "isr" -> isr))
   }
 }
@@ -83,7 +83,7 @@ case class PartitionStateInfo(leaderIsrAndControllerEpoch: LeaderIsrAndControlle
     size
   }
 
-  override def toString(): String = {
+  override def toString: String = {
     val partitionStateInfo = new StringBuilder
     partitionStateInfo.append("(LeaderAndIsrInfo:" + leaderIsrAndControllerEpoch.toString)
     partitionStateInfo.append(",ReplicationFactor:" + replicationFactor + ")")
diff --git a/core/src/main/scala/kafka/api/OffsetRequest.scala b/core/src/main/scala/kafka/api/OffsetRequest.scala
index 59181d1a82d1f..b15cf5a2c6a55 100644
--- a/core/src/main/scala/kafka/api/OffsetRequest.scala
+++ b/core/src/main/scala/kafka/api/OffsetRequest.scala
@@ -109,7 +109,7 @@ case class OffsetRequest(requestInfo: Map[TopicAndPartition, PartitionOffsetRequ
   def isFromOrdinaryClient = replicaId == Request.OrdinaryConsumerId
   def isFromDebuggingClient = replicaId == Request.DebuggingConsumerId
 
-  override def toString(): String = {
+  override def toString: String = {
     describe(true)
   }
 
diff --git a/core/src/main/scala/kafka/api/OffsetResponse.scala b/core/src/main/scala/kafka/api/OffsetResponse.scala
index bfb270fb67f5f..b767c08260725 100644
--- a/core/src/main/scala/kafka/api/OffsetResponse.scala
+++ b/core/src/main/scala/kafka/api/OffsetResponse.scala
@@ -46,7 +46,7 @@ object OffsetResponse {
 
 
 case class PartitionOffsetsResponse(error: Short, offsets: Seq[Long]) {
-  override def toString(): String = {
+  override def toString: String = {
     new String("error: " + Errors.forCode(error).exceptionName + " offsets: " + offsets.mkString)
   }
 }
diff --git a/core/src/main/scala/kafka/api/ProducerRequest.scala b/core/src/main/scala/kafka/api/ProducerRequest.scala
index 30af8410b6afc..aad2fa5fb9bf9 100644
--- a/core/src/main/scala/kafka/api/ProducerRequest.scala
+++ b/core/src/main/scala/kafka/api/ProducerRequest.scala
@@ -124,7 +124,7 @@ case class ProducerRequest(versionId: Short = ProducerRequest.CurrentVersion,
 
   def numPartitions = data.size
 
-  override def toString(): String = {
+  override def toString: String = {
     describe(true)
   }
 
diff --git a/core/src/main/scala/kafka/api/RequestOrResponse.scala b/core/src/main/scala/kafka/api/RequestOrResponse.scala
index 73ec1d9fb811c..65b37fd235e24 100644
--- a/core/src/main/scala/kafka/api/RequestOrResponse.scala
+++ b/core/src/main/scala/kafka/api/RequestOrResponse.scala
@@ -26,7 +26,7 @@ object Request {
   val DebuggingConsumerId: Int = -2
 
   // Broker ids are non-negative int.
-  def isValidBrokerId(brokerId: Int): Boolean = (brokerId >= 0)
+  def isValidBrokerId(brokerId: Int): Boolean = brokerId >= 0
 }
 
 
diff --git a/core/src/main/scala/kafka/api/TopicMetadata.scala b/core/src/main/scala/kafka/api/TopicMetadata.scala
index ae5ea582d063e..815de21660164 100644
--- a/core/src/main/scala/kafka/api/TopicMetadata.scala
+++ b/core/src/main/scala/kafka/api/TopicMetadata.scala
@@ -57,7 +57,7 @@ case class TopicMetadata(topic: String, partitionsMetadata: Seq[PartitionMetadat
     partitionsMetadata.foreach(m => m.writeTo(buffer))
   }
 
-  override def toString(): String = {
+  override def toString: String = {
     val topicMetadataInfo = new StringBuilder
     topicMetadataInfo.append("{TopicMetadata for topic %s -> ".format(topic))
     Errors.forCode(errorCode) match {
@@ -138,7 +138,7 @@ case class PartitionMetadata(partitionId: Int,
     isr.foreach(r => buffer.putInt(r.id))
   }
 
-  override def toString(): String = {
+  override def toString: String = {
     val partitionMetadataString = new StringBuilder
     partitionMetadataString.append("\tpartition " + partitionId)
     partitionMetadataString.append("\tleader: " + (if(leader.isDefined) leader.get.toString else "none"))
diff --git a/core/src/main/scala/kafka/api/TopicMetadataRequest.scala b/core/src/main/scala/kafka/api/TopicMetadataRequest.scala
index 0654e3de22640..107696de891e1 100644
--- a/core/src/main/scala/kafka/api/TopicMetadataRequest.scala
+++ b/core/src/main/scala/kafka/api/TopicMetadataRequest.scala
@@ -57,7 +57,7 @@ case class TopicMetadataRequest(versionId: Short,
     topics.foldLeft(0)(_ + shortStringLength(_)) /* topics */
   }
 
-  override def toString(): String = {
+  override def toString: String = {
     describe(true)
   }
 
diff --git a/core/src/main/scala/kafka/client/ClientUtils.scala b/core/src/main/scala/kafka/client/ClientUtils.scala
index fd1fc26d1b95a..f61a978ffcf00 100755
--- a/core/src/main/scala/kafka/client/ClientUtils.scala
+++ b/core/src/main/scala/kafka/client/ClientUtils.scala
@@ -142,11 +142,11 @@ object ClientUtils extends Logging{
 
      var offsetManagerChannelOpt: Option[BlockingChannel] = None
 
-     while (!offsetManagerChannelOpt.isDefined) {
+     while (offsetManagerChannelOpt.isEmpty) {
 
        var coordinatorOpt: Option[BrokerEndPoint] = None
 
-       while (!coordinatorOpt.isDefined) {
+       while (coordinatorOpt.isEmpty) {
          try {
            if (!queryChannel.isConnected)
              queryChannel = channelToAnyBroker(zkUtils)
diff --git a/core/src/main/scala/kafka/cluster/Cluster.scala b/core/src/main/scala/kafka/cluster/Cluster.scala
index 992c54e0368b3..75bbec054aed8 100644
--- a/core/src/main/scala/kafka/cluster/Cluster.scala
+++ b/core/src/main/scala/kafka/cluster/Cluster.scala
@@ -40,6 +40,6 @@ private[kafka] class Cluster {
   
   def size = brokers.size
   
-  override def toString(): String = 
+  override def toString: String =
     "Cluster(" + brokers.values.mkString(", ") + ")"  
 }
diff --git a/core/src/main/scala/kafka/cluster/Partition.scala b/core/src/main/scala/kafka/cluster/Partition.scala
index ea22e87558137..a561a97037fce 100755
--- a/core/src/main/scala/kafka/cluster/Partition.scala
+++ b/core/src/main/scala/kafka/cluster/Partition.scala
@@ -64,7 +64,7 @@ class Partition(val topic: String,
   private var controllerEpoch: Int = KafkaController.InitialControllerEpoch - 1
   this.logIdent = "Partition [%s,%d] on broker %d: ".format(topic, partitionId, localBrokerId)
 
-  private def isReplicaLocal(replicaId: Int) : Boolean = (replicaId == localBrokerId)
+  private def isReplicaLocal(replicaId: Int) : Boolean = replicaId == localBrokerId
   val tags = Map("topic" -> topic, "partition" -> partitionId.toString)
 
   newGauge("UnderReplicated",
@@ -158,7 +158,7 @@ class Partition(val topic: String,
   }
 
   def getLeaderEpoch(): Int = {
-    return this.leaderEpoch
+    this.leaderEpoch
   }
 
   /**
@@ -381,9 +381,9 @@ class Partition(val topic: String,
       leaderReplicaIfLocal() match {
         case Some(leaderReplica) =>
           val outOfSyncReplicas = getOutOfSyncReplicas(leaderReplica, replicaMaxLagTimeMs)
-          if(outOfSyncReplicas.size > 0) {
+          if(outOfSyncReplicas.nonEmpty) {
             val newInSyncReplicas = inSyncReplicas -- outOfSyncReplicas
-            assert(newInSyncReplicas.size > 0)
+            assert(newInSyncReplicas.nonEmpty)
             info("Shrinking ISR for partition [%s,%d] from %s to %s".format(topic, partitionId,
               inSyncReplicas.map(_.brokerId).mkString(","), newInSyncReplicas.map(_.brokerId).mkString(",")))
             // update ISR in zk and in cache
@@ -421,7 +421,7 @@ class Partition(val topic: String,
     val candidateReplicas = inSyncReplicas - leaderReplica
 
     val laggingReplicas = candidateReplicas.filter(r => (time.milliseconds - r.lastCaughtUpTimeMs) > maxLagMs)
-    if(laggingReplicas.size > 0)
+    if(laggingReplicas.nonEmpty)
       debug("Lagging replicas for partition %s are %s".format(TopicAndPartition(topic, partitionId), laggingReplicas.map(_.brokerId).mkString(",")))
 
     laggingReplicas
@@ -484,7 +484,7 @@ class Partition(val topic: String,
   }
 
   override def equals(that: Any): Boolean = {
-    if(!(that.isInstanceOf[Partition]))
+    if(!that.isInstanceOf[Partition])
       return false
     val other = that.asInstanceOf[Partition]
     if(topic.equals(other.topic) && partitionId == other.partitionId)
@@ -496,7 +496,7 @@ class Partition(val topic: String,
     31 + topic.hashCode() + 17*partitionId
   }
 
-  override def toString(): String = {
+  override def toString: String = {
     val partitionString = new StringBuilder
     partitionString.append("Topic: " + topic)
     partitionString.append("; Partition: " + partitionId)
diff --git a/core/src/main/scala/kafka/cluster/Replica.scala b/core/src/main/scala/kafka/cluster/Replica.scala
index 740e83567c1a1..dfb203ae01831 100644
--- a/core/src/main/scala/kafka/cluster/Replica.scala
+++ b/core/src/main/scala/kafka/cluster/Replica.scala
@@ -98,7 +98,7 @@ class Replica(val brokerId: Int,
   }
 
   override def equals(that: Any): Boolean = {
-    if(!(that.isInstanceOf[Replica]))
+    if(!that.isInstanceOf[Replica])
       return false
     val other = that.asInstanceOf[Replica]
     if(topic.equals(other.topic) && brokerId == other.brokerId && partition.equals(other.partition))
@@ -111,7 +111,7 @@ class Replica(val brokerId: Int,
   }
 
 
-  override def toString(): String = {
+  override def toString: String = {
     val replicaString = new StringBuilder
     replicaString.append("ReplicaId: " + brokerId)
     replicaString.append("; Topic: " + topic)
diff --git a/core/src/main/scala/kafka/common/AppInfo.scala b/core/src/main/scala/kafka/common/AppInfo.scala
index 8e2f49d1fd0e7..f77bdf55a69b0 100644
--- a/core/src/main/scala/kafka/common/AppInfo.scala
+++ b/core/src/main/scala/kafka/common/AppInfo.scala
@@ -42,7 +42,7 @@ object AppInfo extends KafkaMetricsGroup {
     newGauge("CommitID",
       new Gauge[String] {
         def value = {
-          AppInfoParser.getCommitId();
+          AppInfoParser.getCommitId()
         }
       })
 
diff --git a/core/src/main/scala/kafka/common/ZkNodeChangeNotificationListener.scala b/core/src/main/scala/kafka/common/ZkNodeChangeNotificationListener.scala
index baddecc149012..580ae330f3a73 100644
--- a/core/src/main/scala/kafka/common/ZkNodeChangeNotificationListener.scala
+++ b/core/src/main/scala/kafka/common/ZkNodeChangeNotificationListener.scala
@@ -92,7 +92,9 @@ class ZkNodeChangeNotificationListener(private val zkUtils: ZkUtils,
           if (changeId > lastExecutedChange) {
             val changeZnode = seqNodeRoot + "/" + notification
             val (data, stat) = zkUtils.readDataMaybeNull(changeZnode)
-            data map (notificationHandler.processNotification(_)) getOrElse (logger.warn(s"read null data from $changeZnode when processing notification $notification"))
+            data.map(notificationHandler.processNotification(_)).getOrElse {
+              logger.warn(s"read null data from $changeZnode when processing notification $notification")
+            }
           }
           lastExecutedChange = changeId
         }
@@ -107,6 +109,7 @@ class ZkNodeChangeNotificationListener(private val zkUtils: ZkUtils,
 
   /**
    * Purges expired notifications.
+   *
    * @param now
    * @param notifications
    */
diff --git a/core/src/main/scala/kafka/consumer/KafkaStream.scala b/core/src/main/scala/kafka/consumer/KafkaStream.scala
index 805e91677034e..aebf3eaed980a 100644
--- a/core/src/main/scala/kafka/consumer/KafkaStream.scala
+++ b/core/src/main/scala/kafka/consumer/KafkaStream.scala
@@ -45,7 +45,7 @@ class KafkaStream[K,V](private val queue: BlockingQueue[FetchedDataChunk],
     iter.clearCurrentChunk()
   }
 
-  override def toString(): String = {
+  override def toString: String = {
      "%s kafka stream".format(clientId)
   }
 }
diff --git a/core/src/main/scala/kafka/consumer/PartitionAssignor.scala b/core/src/main/scala/kafka/consumer/PartitionAssignor.scala
index 5a1bdd0dee506..96fe6902693b2 100755
--- a/core/src/main/scala/kafka/consumer/PartitionAssignor.scala
+++ b/core/src/main/scala/kafka/consumer/PartitionAssignor.scala
@@ -76,7 +76,7 @@ class RoundRobinAssignor() extends PartitionAssignor with Logging {
     val partitionAssignment =
       new Pool[String, mutable.Map[TopicAndPartition, ConsumerThreadId]](Some(valueFactory))
 
-    if (ctx.consumersForTopic.size > 0) {
+    if (ctx.consumersForTopic.nonEmpty) {
       // check conditions (a) and (b)
       val (headTopic, headThreadIdSet) = (ctx.consumersForTopic.head._1, ctx.consumersForTopic.head._2.toSet)
       ctx.consumersForTopic.foreach { case (topic, threadIds) =>
diff --git a/core/src/main/scala/kafka/consumer/PartitionTopicInfo.scala b/core/src/main/scala/kafka/consumer/PartitionTopicInfo.scala
index 9c779ce072fb0..c7c7836a4b525 100644
--- a/core/src/main/scala/kafka/consumer/PartitionTopicInfo.scala
+++ b/core/src/main/scala/kafka/consumer/PartitionTopicInfo.scala
@@ -67,7 +67,7 @@ class PartitionTopicInfo(val topic: String,
     }
   }
   
-  override def toString(): String = topic + ":" + partitionId.toString + ": fetched offset = " + fetchedOffset.get +
+  override def toString: String = topic + ":" + partitionId.toString + ": fetched offset = " + fetchedOffset.get +
     ": consumed offset = " + consumedOffset.get
 }
 
diff --git a/core/src/main/scala/kafka/controller/ControllerChannelManager.scala b/core/src/main/scala/kafka/controller/ControllerChannelManager.scala
index b4059a4964713..32478ca7a3538 100755
--- a/core/src/main/scala/kafka/controller/ControllerChannelManager.scala
+++ b/core/src/main/scala/kafka/controller/ControllerChannelManager.scala
@@ -257,13 +257,13 @@ class ControllerBrokerRequestBatch(controller: KafkaController) extends  Logging
 
   def newBatch() {
     // raise error if the previous batch is not empty
-    if (leaderAndIsrRequestMap.size > 0)
+    if (leaderAndIsrRequestMap.nonEmpty)
       throw new IllegalStateException("Controller to broker state change requests batch is not empty while creating " +
         "a new one. Some LeaderAndIsr state changes %s might be lost ".format(leaderAndIsrRequestMap.toString()))
-    if (stopReplicaRequestMap.size > 0)
+    if (stopReplicaRequestMap.nonEmpty)
       throw new IllegalStateException("Controller to broker state change requests batch is not empty while creating a " +
         "new one. Some StopReplica state changes %s might be lost ".format(stopReplicaRequestMap.toString()))
-    if (updateMetadataRequestMap.size > 0)
+    if (updateMetadataRequestMap.nonEmpty)
       throw new IllegalStateException("Controller to broker state change requests batch is not empty while creating a " +
         "new one. Some UpdateMetadata state changes %s might be lost ".format(updateMetadataRequestMap.toString()))
   }
@@ -424,15 +424,15 @@ class ControllerBrokerRequestBatch(controller: KafkaController) extends  Logging
       stopReplicaRequestMap.clear()
     } catch {
       case e : Throwable => {
-        if (leaderAndIsrRequestMap.size > 0) {
+        if (leaderAndIsrRequestMap.nonEmpty) {
           error("Haven't been able to send leader and isr requests, current state of " +
               s"the map is $leaderAndIsrRequestMap. Exception message: $e")
         }
-        if (updateMetadataRequestMap.size > 0) {
+        if (updateMetadataRequestMap.nonEmpty) {
           error("Haven't been able to send metadata update requests, current state of " +
               s"the map is $updateMetadataRequestMap. Exception message: $e")
         }
-        if (stopReplicaRequestMap.size > 0) {
+        if (stopReplicaRequestMap.nonEmpty) {
           error("Haven't been able to send stop replica requests, current state of " +
               s"the map is $stopReplicaRequestMap. Exception message: $e")
         }
diff --git a/core/src/main/scala/kafka/controller/KafkaController.scala b/core/src/main/scala/kafka/controller/KafkaController.scala
index d533a85d77002..1584cc95a38ee 100755
--- a/core/src/main/scala/kafka/controller/KafkaController.scala
+++ b/core/src/main/scala/kafka/controller/KafkaController.scala
@@ -71,7 +71,7 @@ class ControllerContext(val zkUtils: ZkUtils,
 
   // getter
   def liveBrokers = liveBrokersUnderlying.filter(broker => !shuttingDownBrokerIds.contains(broker.id))
-  def liveBrokerIds = liveBrokerIdsUnderlying.filter(brokerId => !shuttingDownBrokerIds.contains(brokerId))
+  def liveBrokerIds = liveBrokerIdsUnderlying -- shuttingDownBrokerIds
 
   def liveOrShuttingDownBrokerIds = liveBrokerIdsUnderlying
   def liveOrShuttingDownBrokers = liveBrokersUnderlying
@@ -84,22 +84,23 @@ class ControllerContext(val zkUtils: ZkUtils,
   }
 
   def replicasOnBrokers(brokerIds: Set[Int]): Set[PartitionAndReplica] = {
-    brokerIds.map { brokerId =>
+    brokerIds.flatMap { brokerId =>
       partitionReplicaAssignment
-        .filter { case(topicAndPartition, replicas) => replicas.contains(brokerId) }
-        .map { case(topicAndPartition, replicas) =>
-                 new PartitionAndReplica(topicAndPartition.topic, topicAndPartition.partition, brokerId) }
-    }.flatten.toSet
+        .filter { case (topicAndPartition, replicas) => replicas.contains(brokerId) }
+        .map { case (topicAndPartition, replicas) =>
+          new PartitionAndReplica(topicAndPartition.topic, topicAndPartition.partition, brokerId)
+        }
+    }.toSet
   }
 
   def replicasForTopic(topic: String): Set[PartitionAndReplica] = {
     partitionReplicaAssignment
-      .filter { case(topicAndPartition, replicas) => topicAndPartition.topic.equals(topic) }
-      .map { case(topicAndPartition, replicas) =>
+      .filter { case (topicAndPartition, replicas) => topicAndPartition.topic.equals(topic) }
+      .flatMap { case (topicAndPartition, replicas) =>
         replicas.map { r =>
           new PartitionAndReplica(topicAndPartition.topic, topicAndPartition.partition, r)
         }
-    }.flatten.toSet
+      }.toSet
   }
 
   def partitionsForTopic(topic: String): collection.Set[TopicAndPartition] = {
@@ -112,10 +113,10 @@ class ControllerContext(val zkUtils: ZkUtils,
   }
 
   def replicasForPartition(partitions: collection.Set[TopicAndPartition]): collection.Set[PartitionAndReplica] = {
-    partitions.map { p =>
+    partitions.flatMap { p =>
       val replicas = partitionReplicaAssignment(p)
       replicas.map(r => new PartitionAndReplica(p.topic, p.partition, r))
-    }.flatten
+    }
   }
 
   def removeTopic(topic: String) = {
@@ -139,7 +140,7 @@ object KafkaController extends Logging {
       Json.parseFull(controllerInfoString) match {
         case Some(m) =>
           val controllerInfo = m.asInstanceOf[Map[String, Any]]
-          return controllerInfo.get("brokerid").get.asInstanceOf[Int]
+          controllerInfo.get("brokerid").get.asInstanceOf[Int]
         case None => throw new KafkaException("Failed to parse the controller info json [%s].".format(controllerInfoString))
       }
     } catch {
@@ -148,7 +149,7 @@ object KafkaController extends Logging {
         warn("Failed to parse the controller info as json. "
           + "Probably this controller is still using the old format [%s] to store the broker id in zookeeper".format(controllerInfoString))
         try {
-          return controllerInfoString.toInt
+          controllerInfoString.toInt
         } catch {
           case t: Throwable => throw new KafkaException("Failed to parse the controller info: " + controllerInfoString + ". This is neither the new or the old format.", t)
         }
@@ -298,7 +299,7 @@ class KafkaController(val config : KafkaConfig, zkUtils: ZkUtils, val brokerStat
         controllerContext.partitionLeadershipInfo.filter {
           case (topicAndPartition, leaderIsrAndControllerEpoch) =>
             leaderIsrAndControllerEpoch.leaderAndIsr.leader == id && controllerContext.partitionReplicaAssignment(topicAndPartition).size > 1
-        }.map(_._1)
+        }.keys
       }
       replicatedPartitionsBrokerLeads().toSet
     }
@@ -439,7 +440,7 @@ class KafkaController(val config : KafkaConfig, zkUtils: ZkUtils, val brokerStat
     // check if topic deletion needs to be resumed. If at least one replica that belongs to the topic being deleted exists
     // on the newly restarted brokers, there is a chance that topic deletion can resume
     val replicasForTopicsToBeDeleted = allReplicasOnNewBrokers.filter(p => deleteTopicManager.isTopicQueuedUpForDeletion(p.topic))
-    if(replicasForTopicsToBeDeleted.size > 0) {
+    if(replicasForTopicsToBeDeleted.nonEmpty) {
       info(("Some replicas %s for topics scheduled for deletion %s are on the newly restarted brokers %s. " +
         "Signaling restart of topic deletion for these topics").format(replicasForTopicsToBeDeleted.mkString(","),
         deleteTopicManager.topicsToBeDeleted.mkString(","), newBrokers.mkString(",")))
@@ -479,7 +480,7 @@ class KafkaController(val config : KafkaConfig, zkUtils: ZkUtils, val brokerStat
     replicaStateMachine.handleStateChanges(activeReplicasOnDeadBrokers, OfflineReplica)
     // check if topic deletion state for the dead replicas needs to be updated
     val replicasForTopicsToBeDeleted = allReplicasOnDeadBrokers.filter(p => deleteTopicManager.isTopicQueuedUpForDeletion(p.topic))
-    if(replicasForTopicsToBeDeleted.size > 0) {
+    if(replicasForTopicsToBeDeleted.nonEmpty) {
       // it is required to mark the respective replicas in TopicDeletionFailed state since the replica cannot be
       // deleted when the broker is down. This will prevent the replica from being in TopicDeletionStarted state indefinitely
       // since topic deletion cannot be retried until at least one replica is in TopicDeletionStarted state
@@ -780,9 +781,9 @@ class KafkaController(val config : KafkaConfig, zkUtils: ZkUtils, val brokerStat
     val reassignedPartitions = partitionsBeingReassigned.filter { partition =>
       val replicasOpt = controllerContext.partitionReplicaAssignment.get(partition._1)
       val topicDeleted = replicasOpt.isEmpty
-      val successful = if(!topicDeleted) replicasOpt.get == partition._2.newReplicas else false
+      val successful = if (!topicDeleted) replicasOpt.get == partition._2.newReplicas else false
       topicDeleted || successful
-    }.map(_._1)
+    }.keys
     reassignedPartitions.foreach(p => removePartitionFromReassignedPartitions(p))
     var partitionsToReassign: mutable.Map[TopicAndPartition, ReassignedPartitionsContext] = new mutable.HashMap
     partitionsToReassign ++= partitionsBeingReassigned
@@ -992,7 +993,7 @@ class KafkaController(val config : KafkaConfig, zkUtils: ZkUtils, val brokerStat
                                          newReplicaAssignmentForTopic: Map[TopicAndPartition, Seq[Int]]) {
     try {
       val zkPath = getTopicPath(topicAndPartition.topic)
-      val jsonPartitionMap = zkUtils.replicaAssignmentZkData(newReplicaAssignmentForTopic.map(e => (e._1.partition.toString -> e._2)))
+      val jsonPartitionMap = zkUtils.replicaAssignmentZkData(newReplicaAssignmentForTopic.map(e => e._1.partition.toString -> e._2))
       zkUtils.updatePersistentPath(zkPath, jsonPartitionMap)
       debug("Updated path %s with %s for replica assignment".format(zkPath, jsonPartitionMap))
     } catch {
@@ -1021,6 +1022,7 @@ class KafkaController(val config : KafkaConfig, zkUtils: ZkUtils, val brokerStat
   /**
    * Send the leader information for selected partitions to selected brokers so that they can correctly respond to
    * metadata requests
+   *
    * @param brokers The brokers that the update metadata request should be sent to
    */
   def sendUpdateMetadataRequest(brokers: Seq[Int], partitions: Set[TopicAndPartition] = Set.empty[TopicAndPartition]) {
@@ -1043,6 +1045,7 @@ class KafkaController(val config : KafkaConfig, zkUtils: ZkUtils, val brokerStat
   /**
    * Removes a given partition replica from the ISR; if it is not the current
    * leader and there are sufficient remaining replicas in ISR.
+   *
    * @param topic topic
    * @param partition partition
    * @param replicaId replica Id
@@ -1109,6 +1112,7 @@ class KafkaController(val config : KafkaConfig, zkUtils: ZkUtils, val brokerStat
 
   /**
    * Does not change leader or isr, but just increments the leader epoch
+   *
    * @param topic topic
    * @param partition partition
    * @return the new leaderAndIsr with an incremented leader epoch, or None if leaderAndIsr is empty.
@@ -1162,8 +1166,7 @@ class KafkaController(val config : KafkaConfig, zkUtils: ZkUtils, val brokerStat
      * Called after the zookeeper session has expired and a new session has been created. You would have to re-create
      * any ephemeral nodes here.
      *
-     * @throws Exception
-     *             On any error.
+     * @throws Exception On any error.
      */
     @throws(classOf[Exception])
     def handleNewSession() {
@@ -1219,8 +1222,8 @@ class KafkaController(val config : KafkaConfig, zkUtils: ZkUtils, val brokerStat
                   // do this check only if the broker is live and there are no partitions being reassigned currently
                   // and preferred replica election is not in progress
                   if (controllerContext.liveBrokerIds.contains(leaderBroker) &&
-                      controllerContext.partitionsBeingReassigned.size == 0 &&
-                      controllerContext.partitionsUndergoingPreferredReplicaElection.size == 0 &&
+                      controllerContext.partitionsBeingReassigned.isEmpty &&
+                      controllerContext.partitionsUndergoingPreferredReplicaElection.isEmpty &&
                       !deleteTopicManager.isTopicQueuedUpForDeletion(topicPartition.topic) &&
                       controllerContext.allTopics.contains(topicPartition.topic)) {
                     onPreferredReplicaElection(Set(topicPartition), true)
@@ -1250,6 +1253,7 @@ class PartitionsReassignedListener(controller: KafkaController) extends IZkDataL
 
   /**
    * Invoked when some partitions are reassigned by the admin command
+   *
    * @throws Exception On any error.
    */
   @throws(classOf[Exception])
@@ -1276,8 +1280,8 @@ class PartitionsReassignedListener(controller: KafkaController) extends IZkDataL
 
   /**
    * Called when the leader information stored in zookeeper has been delete. Try to elect as the leader
-   * @throws Exception
-   *             On any error.
+   *
+   * @throws Exception On any error.
    */
   @throws(classOf[Exception])
   def handleDataDeleted(dataPath: String) {
@@ -1293,6 +1297,7 @@ class ReassignedPartitionsIsrChangeListener(controller: KafkaController, topic:
 
   /**
    * Invoked when some partitions need to move leader to preferred replica
+   *
    * @throws Exception On any error.
    */
   @throws(classOf[Exception])
@@ -1343,6 +1348,7 @@ class ReassignedPartitionsIsrChangeListener(controller: KafkaController, topic:
 
 /**
  * Called when leader intimates of isr change
+ *
  * @param controller
  */
 class IsrChangeNotificationListener(controller: KafkaController) extends IZkChildListener with Logging {
@@ -1354,7 +1360,7 @@ class IsrChangeNotificationListener(controller: KafkaController) extends IZkChil
       debug("[IsrChangeNotificationListener] Fired!!!")
       val childrenAsScala: mutable.Buffer[String] = currentChildren.asScala
       try {
-        val topicAndPartitions: immutable.Set[TopicAndPartition] = childrenAsScala.map(x => getTopicAndPartition(x)).flatten.toSet
+        val topicAndPartitions: immutable.Set[TopicAndPartition] = childrenAsScala.flatMap(x => getTopicAndPartition(x)).toSet
         if (topicAndPartitions.nonEmpty) {
           controller.updateLeaderAndIsrCache(topicAndPartitions)
           processUpdateNotifications(topicAndPartitions)
@@ -1417,6 +1423,7 @@ class PreferredReplicaElectionListener(controller: KafkaController) extends IZkD
 
   /**
    * Invoked when some partitions are reassigned by the admin command
+   *
    * @throws Exception On any error.
    */
   @throws(classOf[Exception])
@@ -1425,12 +1432,12 @@ class PreferredReplicaElectionListener(controller: KafkaController) extends IZkD
             .format(dataPath, data.toString))
     inLock(controllerContext.controllerLock) {
       val partitionsForPreferredReplicaElection = PreferredReplicaLeaderElectionCommand.parsePreferredReplicaElectionData(data.toString)
-      if(controllerContext.partitionsUndergoingPreferredReplicaElection.size > 0)
+      if(controllerContext.partitionsUndergoingPreferredReplicaElection.nonEmpty)
         info("These partitions are already undergoing preferred replica election: %s"
           .format(controllerContext.partitionsUndergoingPreferredReplicaElection.mkString(",")))
       val partitions = partitionsForPreferredReplicaElection -- controllerContext.partitionsUndergoingPreferredReplicaElection
       val partitionsForTopicsToBeDeleted = partitions.filter(p => controller.deleteTopicManager.isTopicQueuedUpForDeletion(p.topic))
-      if(partitionsForTopicsToBeDeleted.size > 0) {
+      if(partitionsForTopicsToBeDeleted.nonEmpty) {
         error("Skipping preferred replica election for partitions %s since the respective topics are being deleted"
           .format(partitionsForTopicsToBeDeleted))
       }
@@ -1439,8 +1446,7 @@ class PreferredReplicaElectionListener(controller: KafkaController) extends IZkD
   }
 
   /**
-   * @throws Exception
-   *             On any error.
+   * @throws Exception On any error.
    */
   @throws(classOf[Exception])
   def handleDataDeleted(dataPath: String) {
@@ -1451,13 +1457,13 @@ case class ReassignedPartitionsContext(var newReplicas: Seq[Int] = Seq.empty,
                                        var isrChangeListener: ReassignedPartitionsIsrChangeListener = null)
 
 case class PartitionAndReplica(topic: String, partition: Int, replica: Int) {
-  override def toString(): String = {
+  override def toString: String = {
     "[Topic=%s,Partition=%d,Replica=%d]".format(topic, partition, replica)
   }
 }
 
 case class LeaderIsrAndControllerEpoch(leaderAndIsr: LeaderAndIsr, controllerEpoch: Int) {
-  override def toString(): String = {
+  override def toString: String = {
     val leaderAndIsrInfo = new StringBuilder
     leaderAndIsrInfo.append("(Leader:" + leaderAndIsr.leader)
     leaderAndIsrInfo.append(",ISR:" + leaderAndIsr.isr.mkString(","))
diff --git a/core/src/main/scala/kafka/controller/PartitionLeaderSelector.scala b/core/src/main/scala/kafka/controller/PartitionLeaderSelector.scala
index 682ce1d56bd92..9517523e79309 100644
--- a/core/src/main/scala/kafka/controller/PartitionLeaderSelector.scala
+++ b/core/src/main/scala/kafka/controller/PartitionLeaderSelector.scala
@@ -183,7 +183,7 @@ class ControlledShutdownLeaderSelector(controllerContext: ControllerContext)
     val liveAssignedReplicas = assignedReplicas.filter(r => liveOrShuttingDownBrokerIds.contains(r))
 
     val newIsr = currentLeaderAndIsr.isr.filter(brokerId => !controllerContext.shuttingDownBrokerIds.contains(brokerId))
-    liveAssignedReplicas.filter(newIsr.contains).headOption match {
+    liveAssignedReplicas.find(newIsr.contains) match {
       case Some(newLeader) =>
         debug("Partition %s : current leader = %d, new leader = %d".format(topicAndPartition, currentLeader, newLeader))
         (LeaderAndIsr(newLeader, currentLeaderEpoch + 1, newIsr, currentLeaderIsrZkPathVersion + 1), liveAssignedReplicas)
diff --git a/core/src/main/scala/kafka/controller/PartitionStateMachine.scala b/core/src/main/scala/kafka/controller/PartitionStateMachine.scala
index 47efc51a2d887..bf5fde4a144ea 100755
--- a/core/src/main/scala/kafka/controller/PartitionStateMachine.scala
+++ b/core/src/main/scala/kafka/controller/PartitionStateMachine.scala
@@ -115,7 +115,7 @@ class PartitionStateMachine(controller: KafkaController) extends Logging {
       // try to move all partitions in NewPartition or OfflinePartition state to OnlinePartition state except partitions
       // that belong to topics to be deleted
       for((topicAndPartition, partitionState) <- partitionState
-          if(!controller.deleteTopicManager.isTopicQueuedUpForDeletion(topicAndPartition.topic))) {
+          if !controller.deleteTopicManager.isTopicQueuedUpForDeletion(topicAndPartition.topic)) {
         if(partitionState.equals(OfflinePartition) || partitionState.equals(NewPartition))
           handleStateChange(topicAndPartition.topic, topicAndPartition.partition, OnlinePartition, controller.offlinePartitionSelector,
                             (new CallbackBuilder).build)
@@ -432,7 +432,7 @@ class PartitionStateMachine(controller: KafkaController) extends Logging {
             controllerContext.partitionReplicaAssignment.++=(addedPartitionReplicaAssignment)
             info("New topics: [%s], deleted topics: [%s], new partition replica assignment [%s]".format(newTopics,
               deletedTopics, addedPartitionReplicaAssignment))
-            if(newTopics.size > 0)
+            if(newTopics.nonEmpty)
               controller.onNewTopicCreation(newTopics, addedPartitionReplicaAssignment.keySet.toSet)
           } catch {
             case e: Throwable => error("Error while handling new topic", e )
@@ -463,13 +463,13 @@ class PartitionStateMachine(controller: KafkaController) extends Logging {
           (children: Buffer[String]).toSet
         }
         debug("Delete topics listener fired for topics %s to be deleted".format(topicsToBeDeleted.mkString(",")))
-        val nonExistentTopics = topicsToBeDeleted.filter(t => !controllerContext.allTopics.contains(t))
-        if(nonExistentTopics.size > 0) {
+        val nonExistentTopics = topicsToBeDeleted -- controllerContext.allTopics
+        if(nonExistentTopics.nonEmpty) {
           warn("Ignoring request to delete non-existing topics " + nonExistentTopics.mkString(","))
           nonExistentTopics.foreach(topic => zkUtils.deletePathRecursive(getDeleteTopicPath(topic)))
         }
         topicsToBeDeleted --= nonExistentTopics
-        if(topicsToBeDeleted.size > 0) {
+        if(topicsToBeDeleted.nonEmpty) {
           info("Starting topic deletion for topics " + topicsToBeDeleted.mkString(","))
           // mark topic ineligible for deletion if other state changes are in progress
           topicsToBeDeleted.foreach { topic =>
@@ -512,7 +512,7 @@ class PartitionStateMachine(controller: KafkaController) extends Logging {
             error("Skipping adding partitions %s for topic %s since it is currently being deleted"
                   .format(partitionsToBeAdded.map(_._1.partition).mkString(","), topic))
           else {
-            if (partitionsToBeAdded.size > 0) {
+            if (partitionsToBeAdded.nonEmpty) {
               info("New partitions to be added %s".format(partitionsToBeAdded))
               controllerContext.partitionReplicaAssignment.++=(partitionsToBeAdded)
               controller.onNewPartitionCreation(partitionsToBeAdded.keySet.toSet)
diff --git a/core/src/main/scala/kafka/controller/ReplicaStateMachine.scala b/core/src/main/scala/kafka/controller/ReplicaStateMachine.scala
index d49b6af6e6131..d4e9bb4432e1a 100755
--- a/core/src/main/scala/kafka/controller/ReplicaStateMachine.scala
+++ b/core/src/main/scala/kafka/controller/ReplicaStateMachine.scala
@@ -107,7 +107,7 @@ class ReplicaStateMachine(controller: KafkaController) extends Logging {
    */
   def handleStateChanges(replicas: Set[PartitionAndReplica], targetState: ReplicaState,
                          callbacks: Callbacks = (new CallbackBuilder).build) {
-    if(replicas.size > 0) {
+    if(replicas.nonEmpty) {
       info("Invoking state change to %s for replicas %s".format(targetState, replicas.mkString(",")))
       try {
         brokerRequestBatch.newBatch()
@@ -370,9 +370,9 @@ class ReplicaStateMachine(controller: KafkaController) extends Logging {
                 .format(newBrokerIdsSorted.mkString(","), deadBrokerIdsSorted.mkString(","), liveBrokerIdsSorted.mkString(",")))
               newBrokers.foreach(controllerContext.controllerChannelManager.addBroker)
               deadBrokerIds.foreach(controllerContext.controllerChannelManager.removeBroker)
-              if(newBrokerIds.size > 0)
+              if(newBrokerIds.nonEmpty)
                 controller.onBrokerStartup(newBrokerIdsSorted)
-              if(deadBrokerIds.size > 0)
+              if(deadBrokerIds.nonEmpty)
                 controller.onBrokerFailure(deadBrokerIdsSorted)
             } catch {
               case e: Throwable => error("Error while handling broker changes", e)
diff --git a/core/src/main/scala/kafka/controller/TopicDeletionManager.scala b/core/src/main/scala/kafka/controller/TopicDeletionManager.scala
index c6f80ac87a0ae..f24c69ca22bd4 100755
--- a/core/src/main/scala/kafka/controller/TopicDeletionManager.scala
+++ b/core/src/main/scala/kafka/controller/TopicDeletionManager.scala
@@ -95,7 +95,7 @@ class TopicDeletionManager(controller: KafkaController,
   def start() {
     if (isDeleteTopicEnabled) {
       deleteTopicsThread = new DeleteTopicsThread()
-      if (topicsToBeDeleted.size > 0)
+      if (topicsToBeDeleted.nonEmpty)
         deleteTopicStateChanged.set(true)
       deleteTopicsThread.start()
     }
@@ -142,7 +142,7 @@ class TopicDeletionManager(controller: KafkaController,
   def resumeDeletionForTopics(topics: Set[String] = Set.empty) {
     if(isDeleteTopicEnabled) {
       val topicsToResumeDeletion = topics & topicsToBeDeleted
-      if(topicsToResumeDeletion.size > 0) {
+      if(topicsToResumeDeletion.nonEmpty) {
         topicsIneligibleForDeletion --= topicsToResumeDeletion
         resumeTopicDeletionThread()
       }
@@ -160,7 +160,7 @@ class TopicDeletionManager(controller: KafkaController,
   def failReplicaDeletion(replicas: Set[PartitionAndReplica]) {
     if(isDeleteTopicEnabled) {
       val replicasThatFailedToDelete = replicas.filter(r => isTopicQueuedUpForDeletion(r.topic))
-      if(replicasThatFailedToDelete.size > 0) {
+      if(replicasThatFailedToDelete.nonEmpty) {
         val topics = replicasThatFailedToDelete.map(_.topic)
         debug("Deletion failed for replicas %s. Halting deletion for topics %s"
           .format(replicasThatFailedToDelete.mkString(","), topics))
@@ -182,7 +182,7 @@ class TopicDeletionManager(controller: KafkaController,
     if(isDeleteTopicEnabled) {
       val newTopicsToHaltDeletion = topicsToBeDeleted & topics
       topicsIneligibleForDeletion ++= newTopicsToHaltDeletion
-      if(newTopicsToHaltDeletion.size > 0)
+      if(newTopicsToHaltDeletion.nonEmpty)
         info("Halted deletion of topics %s".format(newTopicsToHaltDeletion.mkString(",")))
     }
   }
@@ -310,7 +310,7 @@ class TopicDeletionManager(controller: KafkaController,
     controller.sendUpdateMetadataRequest(controllerContext.liveOrShuttingDownBrokerIds.toSeq, partitions)
     val partitionReplicaAssignmentByTopic = controllerContext.partitionReplicaAssignment.groupBy(p => p._1.topic)
     topics.foreach { topic =>
-      onPartitionDeletion(partitionReplicaAssignmentByTopic(topic).map(_._1).toSet)
+      onPartitionDeletion(partitionReplicaAssignmentByTopic(topic).keySet)
     }
   }
 
@@ -343,7 +343,7 @@ class TopicDeletionManager(controller: KafkaController,
       debug("Deletion started for replicas %s".format(replicasForDeletionRetry.mkString(",")))
       controller.replicaStateMachine.handleStateChanges(replicasForDeletionRetry, ReplicaDeletionStarted,
         new Callbacks.CallbackBuilder().stopReplicaCallback(deleteTopicStopReplicaCallback).build)
-      if(deadReplicasForTopic.size > 0) {
+      if(deadReplicasForTopic.nonEmpty) {
         debug("Dead Replicas (%s) found for topic %s".format(deadReplicasForTopic.mkString(","), topic))
         markTopicIneligibleForDeletion(Set(topic))
       }
@@ -373,7 +373,7 @@ class TopicDeletionManager(controller: KafkaController,
     val responseMap = stopReplicaResponse.responses.asScala
     val partitionsInError =
       if (stopReplicaResponse.errorCode != Errors.NONE.code) responseMap.keySet
-      else responseMap.filter { case (_, error) => error != Errors.NONE.code }.map(_._1).toSet
+      else responseMap.filter { case (_, error) => error != Errors.NONE.code }.keySet
     val replicasInError = partitionsInError.map(p => PartitionAndReplica(p.topic, p.partition, replicaId))
     inLock(controllerContext.controllerLock) {
       // move all the failed replicas to ReplicaDeletionIneligible
@@ -397,7 +397,7 @@ class TopicDeletionManager(controller: KafkaController,
       inLock(controllerContext.controllerLock) {
         val topicsQueuedForDeletion = Set.empty[String] ++ topicsToBeDeleted
 
-        if(!topicsQueuedForDeletion.isEmpty)
+        if(topicsQueuedForDeletion.nonEmpty)
           info("Handling deletion for topics " + topicsQueuedForDeletion.mkString(","))
 
         topicsQueuedForDeletion.foreach { topic =>
diff --git a/core/src/main/scala/kafka/coordinator/GroupCoordinator.scala b/core/src/main/scala/kafka/coordinator/GroupCoordinator.scala
index f4457647ece83..e9bbbd36c69ae 100644
--- a/core/src/main/scala/kafka/coordinator/GroupCoordinator.scala
+++ b/core/src/main/scala/kafka/coordinator/GroupCoordinator.scala
@@ -647,7 +647,7 @@ class GroupCoordinator(val brokerId: Int,
   def onCompleteJoin(group: GroupMetadata) {
     group synchronized {
       val failedMembers = group.notYetRejoinedMembers
-      if (group.isEmpty || !failedMembers.isEmpty) {
+      if (group.isEmpty || failedMembers.nonEmpty) {
         failedMembers.foreach { failedMember =>
           group.remove(failedMember.memberId)
           // TODO: cut the socket connection to the client
diff --git a/core/src/main/scala/kafka/coordinator/GroupMetadataManager.scala b/core/src/main/scala/kafka/coordinator/GroupMetadataManager.scala
index c6bc44ef5efb5..b968f976ce0ed 100644
--- a/core/src/main/scala/kafka/coordinator/GroupMetadataManager.scala
+++ b/core/src/main/scala/kafka/coordinator/GroupMetadataManager.scala
@@ -108,7 +108,7 @@ class GroupMetadataManager(val brokerId: Int,
 
   def isGroupLoading(groupId: String): Boolean = loadingPartitions synchronized loadingPartitions.contains(partitionFor(groupId))
 
-  def isLoading(): Boolean = loadingPartitions synchronized !loadingPartitions.isEmpty
+  def isLoading(): Boolean = loadingPartitions synchronized loadingPartitions.nonEmpty
 
   /**
    * Get the group associated with the given groupId, or null if not found
diff --git a/core/src/main/scala/kafka/coordinator/MemberMetadata.scala b/core/src/main/scala/kafka/coordinator/MemberMetadata.scala
index 1d799f24d8906..c57b9904ab6cf 100644
--- a/core/src/main/scala/kafka/coordinator/MemberMetadata.scala
+++ b/core/src/main/scala/kafka/coordinator/MemberMetadata.scala
@@ -90,7 +90,7 @@ private[coordinator] class MemberMetadata(val memberId: String,
       if (p1._1 != p2._1 || !util.Arrays.equals(p1._2, p2._2))
         return false
     }
-    return true
+    true
   }
 
   def summary(protocol: String): MemberSummary = {
diff --git a/core/src/main/scala/kafka/javaapi/TopicMetadataRequest.scala b/core/src/main/scala/kafka/javaapi/TopicMetadataRequest.scala
index 92d90732eb6f1..f625ba0f99259 100644
--- a/core/src/main/scala/kafka/javaapi/TopicMetadataRequest.scala
+++ b/core/src/main/scala/kafka/javaapi/TopicMetadataRequest.scala
@@ -44,7 +44,7 @@ class TopicMetadataRequest(val versionId: Short,
 
   def sizeInBytes: Int = underlying.sizeInBytes()
 
-  override def toString(): String = {
+  override def toString: String = {
     describe(true)
   }
 
diff --git a/core/src/main/scala/kafka/log/Log.scala b/core/src/main/scala/kafka/log/Log.scala
index 62dc7a1788408..76cd86e5a2780 100644
--- a/core/src/main/scala/kafka/log/Log.scala
+++ b/core/src/main/scala/kafka/log/Log.scala
@@ -802,7 +802,7 @@ class Log(val dir: File,
     }
   }
 
-  override def toString() = "Log(" + dir + ")"
+  override def toString = "Log(" + dir + ")"
 
   /**
    * This method performs an asynchronous log segment delete by doing the following:
diff --git a/core/src/main/scala/kafka/log/LogSegment.scala b/core/src/main/scala/kafka/log/LogSegment.scala
index 37f757985a5c1..6bbc50c7c3c06 100755
--- a/core/src/main/scala/kafka/log/LogSegment.scala
+++ b/core/src/main/scala/kafka/log/LogSegment.scala
@@ -203,7 +203,7 @@ class LogSegment(val log: FileMessageSet,
     truncated
   }
 
-  override def toString() = "LogSegment(baseOffset=" + baseOffset + ", size=" + size + ")"
+  override def toString = "LogSegment(baseOffset=" + baseOffset + ", size=" + size + ")"
 
   /**
    * Truncate off all index and log entries with offsets >= the given offset.
diff --git a/core/src/main/scala/kafka/message/Message.scala b/core/src/main/scala/kafka/message/Message.scala
index 2ab2e0cd2e0aa..bb91078c637ac 100755
--- a/core/src/main/scala/kafka/message/Message.scala
+++ b/core/src/main/scala/kafka/message/Message.scala
@@ -402,7 +402,7 @@ class Message(val buffer: ByteBuffer,
       throw new IllegalArgumentException(s"Invalid timestamp $timestamp. Timestamp must be ${NoTimestamp} when magic = ${MagicValue_V0}")
   }
 
-  override def toString(): String = {
+  override def toString: String = {
     if (magic == MagicValue_V0)
       s"Message(magic = $magic, attributes = $attributes, crc = $checksum, key = $key, payload = $payload)"
     else
diff --git a/core/src/main/scala/kafka/metrics/KafkaMetricsReporter.scala b/core/src/main/scala/kafka/metrics/KafkaMetricsReporter.scala
index 0d6da3466fd59..999b2a43acea0 100755
--- a/core/src/main/scala/kafka/metrics/KafkaMetricsReporter.scala
+++ b/core/src/main/scala/kafka/metrics/KafkaMetricsReporter.scala
@@ -54,12 +54,14 @@ object KafkaMetricsReporter {
     ReporterStarted synchronized {
       if (!ReporterStarted.get()) {
         val metricsConfig = new KafkaMetricsConfig(verifiableProps)
-        if(metricsConfig.reporters.size > 0) {
+        if(metricsConfig.reporters.nonEmpty) {
           metricsConfig.reporters.foreach(reporterType => {
             val reporter = CoreUtils.createObject[KafkaMetricsReporter](reporterType)
             reporter.init(verifiableProps)
-            if (reporter.isInstanceOf[KafkaMetricsReporterMBean])
-              CoreUtils.registerMBean(reporter, reporter.asInstanceOf[KafkaMetricsReporterMBean].getMBeanName)
+            reporter match {
+              case bean: KafkaMetricsReporterMBean => CoreUtils.registerMBean(reporter, bean.getMBeanName)
+              case _ =>
+            }
           })
           ReporterStarted.set(true)
         }
diff --git a/core/src/main/scala/kafka/network/RequestOrResponseSend.scala b/core/src/main/scala/kafka/network/RequestOrResponseSend.scala
index 364f24bdc5625..153d636103b15 100644
--- a/core/src/main/scala/kafka/network/RequestOrResponseSend.scala
+++ b/core/src/main/scala/kafka/network/RequestOrResponseSend.scala
@@ -26,7 +26,7 @@ import org.apache.kafka.common.network.NetworkSend
 
 object RequestOrResponseSend {
   def serialize(request: RequestOrResponse): ByteBuffer = {
-    val buffer = ByteBuffer.allocate(request.sizeInBytes + (if(request.requestId != None) 2 else 0))
+    val buffer = ByteBuffer.allocate(request.sizeInBytes + (if(request.requestId.isDefined) 2 else 0))
     request.requestId match {
       case Some(requestId) =>
         buffer.putShort(requestId)
diff --git a/core/src/main/scala/kafka/producer/BrokerPartitionInfo.scala b/core/src/main/scala/kafka/producer/BrokerPartitionInfo.scala
index 4616c7e623c06..97289a11875ad 100644
--- a/core/src/main/scala/kafka/producer/BrokerPartitionInfo.scala
+++ b/core/src/main/scala/kafka/producer/BrokerPartitionInfo.scala
@@ -55,7 +55,7 @@ class BrokerPartitionInfo(producerConfig: ProducerConfig,
           }
       }
     val partitionMetadata = metadata.partitionsMetadata
-    if(partitionMetadata.size == 0) {
+    if(partitionMetadata.isEmpty) {
       if(metadata.errorCode != Errors.NONE.code) {
         throw new KafkaException(Errors.forCode(metadata.errorCode).exception)
       } else {
diff --git a/core/src/main/scala/kafka/producer/ProducerRequestStats.scala b/core/src/main/scala/kafka/producer/ProducerRequestStats.scala
index 8ab948a368047..92bbbcfa807dc 100644
--- a/core/src/main/scala/kafka/producer/ProducerRequestStats.scala
+++ b/core/src/main/scala/kafka/producer/ProducerRequestStats.scala
@@ -30,7 +30,7 @@ class ProducerRequestMetrics(metricId: ClientIdBroker) extends KafkaMetricsGroup
 
   val requestTimer = new KafkaTimer(newTimer("ProducerRequestRateAndTimeMs", TimeUnit.MILLISECONDS, TimeUnit.SECONDS, tags))
   val requestSizeHist = newHistogram("ProducerRequestSize", biased = true, tags)
-  val throttleTimeStats = newTimer("ProducerRequestThrottleRateAndTimeMs", TimeUnit.MILLISECONDS, TimeUnit.SECONDS, tags);
+  val throttleTimeStats = newTimer("ProducerRequestThrottleRateAndTimeMs", TimeUnit.MILLISECONDS, TimeUnit.SECONDS, tags)
 }
 
 /**
diff --git a/core/src/main/scala/kafka/producer/async/DefaultEventHandler.scala b/core/src/main/scala/kafka/producer/async/DefaultEventHandler.scala
index b79e64b9a57ef..f9591ade95f34 100755
--- a/core/src/main/scala/kafka/producer/async/DefaultEventHandler.scala
+++ b/core/src/main/scala/kafka/producer/async/DefaultEventHandler.scala
@@ -66,7 +66,7 @@ class DefaultEventHandler[K,V](config: ProducerConfig,
     var remainingRetries = config.messageSendMaxRetries + 1
     val correlationIdStart = correlationId.get()
     debug("Handling %d events".format(events.size))
-    while (remainingRetries > 0 && outstandingProduceRequests.size > 0) {
+    while (remainingRetries > 0 && outstandingProduceRequests.nonEmpty) {
       topicMetadataToRefresh ++= outstandingProduceRequests.map(_.topic)
       if (topicMetadataRefreshInterval >= 0 &&
           SystemTime.milliseconds - lastTopicMetadataRefreshTime > topicMetadataRefreshInterval) {
@@ -76,7 +76,7 @@ class DefaultEventHandler[K,V](config: ProducerConfig,
         lastTopicMetadataRefreshTime = SystemTime.milliseconds
       }
       outstandingProduceRequests = dispatchSerializedData(outstandingProduceRequests)
-      if (outstandingProduceRequests.size > 0) {
+      if (outstandingProduceRequests.nonEmpty) {
         info("Back off for %d ms before retrying send. Remaining retries = %d".format(config.retryBackoffMs, remainingRetries-1))
         // back off and update the topic metadata cache before attempting another send operation
         Thread.sleep(config.retryBackoffMs)
@@ -87,7 +87,7 @@ class DefaultEventHandler[K,V](config: ProducerConfig,
         producerStats.resendRate.mark()
       }
     }
-    if(outstandingProduceRequests.size > 0) {
+    if(outstandingProduceRequests.nonEmpty) {
       producerStats.failedSendRate.mark()
       val correlationIdEnd = correlationId.get()
       error("Failed to send requests for topics %s with correlation ids in [%d,%d]"
@@ -261,9 +261,9 @@ class DefaultEventHandler[K,V](config: ProducerConfig,
    */
   private def send(brokerId: Int, messagesPerTopic: collection.mutable.Map[TopicAndPartition, ByteBufferMessageSet]) = {
     if(brokerId < 0) {
-      warn("Failed to send data since partitions %s don't have a leader".format(messagesPerTopic.map(_._1).mkString(",")))
+      warn("Failed to send data since partitions %s don't have a leader".format(messagesPerTopic.keys.mkString(",")))
       messagesPerTopic.keys.toSeq
-    } else if(messagesPerTopic.size > 0) {
+    } else if(messagesPerTopic.nonEmpty) {
       val currentCorrelationId = correlationId.getAndIncrement
       val producerRequest = new ProducerRequest(currentCorrelationId, config.clientId, config.requestRequiredAcks,
         config.requestTimeoutMs, messagesPerTopic)
@@ -285,7 +285,7 @@ class DefaultEventHandler[K,V](config: ProducerConfig,
           }
           val failedPartitionsAndStatus = response.status.filter(_._2.error != Errors.NONE.code).toSeq
           failedTopicPartitions = failedPartitionsAndStatus.map(partitionStatus => partitionStatus._1)
-          if(failedTopicPartitions.size > 0) {
+          if(failedTopicPartitions.nonEmpty) {
             val errorString = failedPartitionsAndStatus
               .sortWith((p1, p2) => p1._1.topic.compareTo(p2._1.topic) < 0 ||
                                     (p1._1.topic.compareTo(p2._1.topic) == 0 && p1._1.partition < p2._1.partition))
@@ -302,7 +302,7 @@ class DefaultEventHandler[K,V](config: ProducerConfig,
       } catch {
         case t: Throwable =>
           warn("Failed to send producer request with correlation id %d to broker %d with data for partitions %s"
-            .format(currentCorrelationId, brokerId, messagesPerTopic.map(_._1).mkString(",")), t)
+            .format(currentCorrelationId, brokerId, messagesPerTopic.keys.mkString(",")), t)
           messagesPerTopic.keys.toSeq
       }
     } else {
diff --git a/core/src/main/scala/kafka/security/auth/SimpleAclAuthorizer.scala b/core/src/main/scala/kafka/security/auth/SimpleAclAuthorizer.scala
index 18fff453e0858..a36a07d0006c0 100644
--- a/core/src/main/scala/kafka/security/auth/SimpleAclAuthorizer.scala
+++ b/core/src/main/scala/kafka/security/auth/SimpleAclAuthorizer.scala
@@ -154,7 +154,7 @@ class SimpleAclAuthorizer extends Authorizer with Logging {
   }
 
   def isSuperUser(operation: Operation, resource: Resource, principal: KafkaPrincipal, host: String): Boolean = {
-    if (superUsers.exists( _ == principal)) {
+    if (superUsers.contains(principal)) {
       authorizerLogger.debug(s"principal = $principal is a super user, allowing operation without checking acls.")
       true
     } else false
@@ -275,7 +275,7 @@ class SimpleAclAuthorizer extends Authorizer with Logging {
       val newAcls = getNewAcls(currentVersionedAcls.acls)
       val data = Json.encode(Acl.toJsonCompatibleMap(newAcls))
       val (updateSucceeded, updateVersion) =
-        if (!newAcls.isEmpty) {
+        if (newAcls.nonEmpty) {
          updatePath(path, data, currentVersionedAcls.zkVersion)
         } else {
           trace(s"Deleting path for $resource because it had no ACLs remaining")
@@ -285,7 +285,7 @@ class SimpleAclAuthorizer extends Authorizer with Logging {
       if (!updateSucceeded) {
         trace(s"Failed to update ACLs for $resource. Used version ${currentVersionedAcls.zkVersion}. Reading data and retrying update.")
         Thread.sleep(backoffTime)
-        currentVersionedAcls = getAclsFromZk(resource);
+        currentVersionedAcls = getAclsFromZk(resource)
         retries += 1
       } else {
         newVersionedAcls = VersionedAcls(newAcls, updateVersion)
diff --git a/core/src/main/scala/kafka/server/ClientQuotaManager.scala b/core/src/main/scala/kafka/server/ClientQuotaManager.scala
index 5863c72c03739..c99ba97603422 100644
--- a/core/src/main/scala/kafka/server/ClientQuotaManager.scala
+++ b/core/src/main/scala/kafka/server/ClientQuotaManager.scala
@@ -157,7 +157,7 @@ class ClientQuotaManager(private val config: ClientQuotaManagerConfig,
    * Returns the quota for the specified clientId
    */
   def quota(clientId: String): Quota =
-    if (overriddenQuota.containsKey(clientId)) overriddenQuota.get(clientId) else defaultQuota;
+    if (overriddenQuota.containsKey(clientId)) overriddenQuota.get(clientId) else defaultQuota
 
   /*
    * This function either returns the sensors for a given client id or creates them if they don't exist
diff --git a/core/src/main/scala/kafka/server/DelayedOperation.scala b/core/src/main/scala/kafka/server/DelayedOperation.scala
index 220556891584f..5248edfac1667 100644
--- a/core/src/main/scala/kafka/server/DelayedOperation.scala
+++ b/core/src/main/scala/kafka/server/DelayedOperation.scala
@@ -175,7 +175,7 @@ class DelayedOperationPurgatory[T <: DelayedOperation](purgatoryName: String,
    * @return true iff the delayed operations can be completed by the caller
    */
   def tryCompleteElseWatch(operation: T, watchKeys: Seq[Any]): Boolean = {
-    assert(watchKeys.size > 0, "The watch key list can't be empty")
+    assert(watchKeys.nonEmpty, "The watch key list can't be empty")
 
     // The cost of tryComplete() is typically proportional to the number of keys. Calling
     // tryComplete() for each key is going to be expensive if there are many keys. Instead,
diff --git a/core/src/main/scala/kafka/server/KafkaApis.scala b/core/src/main/scala/kafka/server/KafkaApis.scala
index 1edc16242db5c..ebd173226c396 100644
--- a/core/src/main/scala/kafka/server/KafkaApis.scala
+++ b/core/src/main/scala/kafka/server/KafkaApis.scala
@@ -293,7 +293,7 @@ class KafkaApis(val requestChannel: RequestChannel,
         val currentTimestamp = SystemTime.milliseconds
         val defaultExpireTimestamp = offsetRetention + currentTimestamp
         val partitionData = authorizedRequestInfo.mapValues { partitionData =>
-          val metadata = if (partitionData.metadata == null) OffsetMetadata.NoMetadata else partitionData.metadata;
+          val metadata = if (partitionData.metadata == null) OffsetMetadata.NoMetadata else partitionData.metadata
           new OffsetAndMetadata(
             offsetMetadata = OffsetMetadata(partitionData.offset, metadata),
             commitTimestamp = currentTimestamp,
diff --git a/core/src/main/scala/kafka/server/KafkaConfig.scala b/core/src/main/scala/kafka/server/KafkaConfig.scala
index a6644847f41e2..ca66f9d05c04f 100755
--- a/core/src/main/scala/kafka/server/KafkaConfig.scala
+++ b/core/src/main/scala/kafka/server/KafkaConfig.scala
@@ -1002,7 +1002,7 @@ class KafkaConfig(val props: java.util.Map[_, _], doLog: Boolean) extends Abstra
     require(logRollTimeMillis >= 1, "log.roll.ms must be equal or greater than 1")
     require(logRollTimeJitterMillis >= 0, "log.roll.jitter.ms must be equal or greater than 0")
     require(logRetentionTimeMillis >= 1 || logRetentionTimeMillis == -1, "log.retention.ms must be unlimited (-1) or, equal or greater than 1")
-    require(logDirs.size > 0)
+    require(logDirs.nonEmpty)
     require(logCleanerDedupeBufferSize / logCleanerThreads > 1024 * 1024, "log.cleaner.dedupe.buffer.size must be at least 1MB per cleaner thread.")
     require(replicaFetchWaitMaxMs <= replicaSocketTimeoutMs, "replica.socket.timeout.ms should always be at least replica.fetch.wait.max.ms" +
       " to prevent unnecessary socket timeouts")
diff --git a/core/src/main/scala/kafka/server/KafkaServer.scala b/core/src/main/scala/kafka/server/KafkaServer.scala
index f95d9ef74039d..994e28e647629 100755
--- a/core/src/main/scala/kafka/server/KafkaServer.scala
+++ b/core/src/main/scala/kafka/server/KafkaServer.scala
@@ -475,7 +475,7 @@ class KafkaServer(val config: KafkaConfig, time: Time = SystemTime, threadNamePr
               response = channel.receive()
               val shutdownResponse = kafka.api.ControlledShutdownResponse.readFrom(response.payload())
               if (shutdownResponse.errorCode == Errors.NONE.code && shutdownResponse.partitionsRemaining != null &&
-                shutdownResponse.partitionsRemaining.size == 0) {
+                shutdownResponse.partitionsRemaining.isEmpty) {
                 shutdownSucceeded = true
                 info ("Controlled shutdown succeeded")
               }
@@ -649,7 +649,7 @@ class KafkaServer(val config: KafkaConfig, time: Time = SystemTime, threadNamePr
         s"Configured broker.id $brokerId doesn't match stored broker.id ${brokerIdSet.last} in meta.properties. " +
         s"If you moved your data, make sure your configured broker.id matches. " +
         s"If you intend to create a new broker, you should remove all data in your data directories (log.dirs).")
-    else if(brokerIdSet.size == 0 && brokerId < 0 && config.brokerIdGenerationEnable)  // generate a new brokerId from Zookeeper
+    else if(brokerIdSet.isEmpty && brokerId < 0 && config.brokerIdGenerationEnable)  // generate a new brokerId from Zookeeper
       brokerId = generateBrokerId
     else if(brokerIdSet.size == 1) // pick broker.id from meta.properties
       brokerId = brokerIdSet.last
diff --git a/core/src/main/scala/kafka/server/ReplicaManager.scala b/core/src/main/scala/kafka/server/ReplicaManager.scala
index 68f23859ee77b..447fb4051eeb6 100644
--- a/core/src/main/scala/kafka/server/ReplicaManager.scala
+++ b/core/src/main/scala/kafka/server/ReplicaManager.scala
@@ -359,9 +359,8 @@ class ReplicaManager(val config: KafkaConfig,
       // Just return an error and don't handle the request at all
       val responseStatus = messagesPerPartition.map {
         case (topicAndPartition, messageSet) =>
-          (topicAndPartition -> new PartitionResponse(Errors.INVALID_REQUIRED_ACKS.code,
-                                                      LogAppendInfo.UnknownLogAppendInfo.firstOffset,
-                                                      Message.NoTimestamp))
+          topicAndPartition -> new PartitionResponse(Errors.INVALID_REQUIRED_ACKS.code,
+            LogAppendInfo.UnknownLogAppendInfo.firstOffset, Message.NoTimestamp)
       }
       responseCallback(responseStatus)
     }
@@ -375,7 +374,7 @@ class ReplicaManager(val config: KafkaConfig,
   private def delayedRequestRequired(requiredAcks: Short, messagesPerPartition: Map[TopicPartition, MessageSet],
                                        localProduceResults: Map[TopicPartition, LogAppendResult]): Boolean = {
     requiredAcks == -1 &&
-    messagesPerPartition.size > 0 &&
+    messagesPerPartition.nonEmpty &&
     localProduceResults.values.count(_.error.isDefined) < messagesPerPartition.size
   }
 
@@ -639,13 +638,13 @@ class ReplicaManager(val config: KafkaConfig,
         val partitionsTobeLeader = partitionState.filter { case (partition, stateInfo) =>
           stateInfo.leader == config.brokerId
         }
-        val partitionsToBeFollower = (partitionState -- partitionsTobeLeader.keys)
+        val partitionsToBeFollower = partitionState -- partitionsTobeLeader.keys
 
-        val partitionsBecomeLeader = if (!partitionsTobeLeader.isEmpty)
+        val partitionsBecomeLeader = if (partitionsTobeLeader.nonEmpty)
           makeLeaders(controllerId, controllerEpoch, partitionsTobeLeader, correlationId, responseMap)
         else
           Set.empty[Partition]
-        val partitionsBecomeFollower = if (!partitionsToBeFollower.isEmpty)
+        val partitionsBecomeFollower = if (partitionsToBeFollower.nonEmpty)
           makeFollowers(controllerId, controllerEpoch, partitionsToBeFollower, correlationId, responseMap, metadataCache)
         else
           Set.empty[Partition]
diff --git a/core/src/main/scala/kafka/tools/ConsumerPerformance.scala b/core/src/main/scala/kafka/tools/ConsumerPerformance.scala
index 6480ff5ae4ddd..8e5dcc89ed61d 100644
--- a/core/src/main/scala/kafka/tools/ConsumerPerformance.scala
+++ b/core/src/main/scala/kafka/tools/ConsumerPerformance.scala
@@ -91,7 +91,7 @@ object ConsumerPerformance {
     val elapsedSecs = (endMs - startMs) / 1000.0
     if (!config.showDetailedStats) {
       val totalMBRead = (totalBytesRead.get * 1.0) / (1024 * 1024)
-      println(("%s, %s, %.4f, %.4f, %d, %.4f").format(config.dateFormat.format(startMs), config.dateFormat.format(endMs),
+      println("%s, %s, %.4f, %.4f, %d, %.4f".format(config.dateFormat.format(startMs), config.dateFormat.format(endMs),
         totalMBRead, totalMBRead / elapsedSecs, totalMessagesRead.get, totalMessagesRead.get / elapsedSecs))
     }
   }
@@ -156,7 +156,7 @@ object ConsumerPerformance {
     val elapsedMs: Double = endMs - startMs
     val totalMBRead = (bytesRead * 1.0) / (1024 * 1024)
     val mbRead = ((bytesRead - lastBytesRead) * 1.0) / (1024 * 1024)
-    println(("%s, %d, %.4f, %.4f, %d, %.4f").format(dateFormat.format(endMs), id, totalMBRead,
+    println("%s, %d, %.4f, %.4f, %d, %.4f".format(dateFormat.format(endMs), id, totalMBRead,
         1000.0 * (mbRead / elapsedMs), messagesRead, ((messagesRead - lastMessagesRead) / elapsedMs) * 1000.0))
   }
 
diff --git a/core/src/main/scala/kafka/tools/ProducerPerformance.scala b/core/src/main/scala/kafka/tools/ProducerPerformance.scala
index cf2000b9272eb..d4c0f34b76b24 100644
--- a/core/src/main/scala/kafka/tools/ProducerPerformance.scala
+++ b/core/src/main/scala/kafka/tools/ProducerPerformance.scala
@@ -63,7 +63,7 @@ object ProducerPerformance extends Logging {
     val endMs = System.currentTimeMillis
     val elapsedSecs = (endMs - startMs) / 1000.0
     val totalMBSent = (totalBytesSent.get * 1.0) / (1024 * 1024)
-    println(("%s, %s, %d, %d, %d, %.2f, %.4f, %d, %.4f").format(
+    println("%s, %s, %d, %d, %d, %.2f, %.4f, %d, %.4f".format(
       config.dateFormat.format(startMs), config.dateFormat.format(endMs),
       config.compressionCodec.codec, config.messageSize, config.batchSize, totalMBSent,
       totalMBSent / elapsedSecs, totalMessagesSent.get, totalMessagesSent.get / elapsedSecs))
diff --git a/core/src/main/scala/kafka/tools/ReplicaVerificationTool.scala b/core/src/main/scala/kafka/tools/ReplicaVerificationTool.scala
index 71bf0c0407d4f..9a059dfc8da70 100644
--- a/core/src/main/scala/kafka/tools/ReplicaVerificationTool.scala
+++ b/core/src/main/scala/kafka/tools/ReplicaVerificationTool.scala
@@ -180,7 +180,7 @@ object ReplicaVerificationTool extends Logging {
                            fetchSize = fetchSize,
                            maxWait = maxWaitMs,
                            minBytes = 1,
-                           doVerification = (brokerId == verificationBrokerId))
+                           doVerification = brokerId == verificationBrokerId)
     }
 
     Runtime.getRuntime.addShutdownHook(new Thread() {
diff --git a/core/src/main/scala/kafka/tools/SimpleConsumerPerformance.scala b/core/src/main/scala/kafka/tools/SimpleConsumerPerformance.scala
index 5e3c605248fd7..3abbc40dc55da 100644
--- a/core/src/main/scala/kafka/tools/SimpleConsumerPerformance.scala
+++ b/core/src/main/scala/kafka/tools/SimpleConsumerPerformance.scala
@@ -92,7 +92,7 @@ object SimpleConsumerPerformance {
           val reportTime = System.currentTimeMillis
           val elapsed = (reportTime - lastReportTime)/1000.0
           val totalMBRead = ((totalBytesRead-lastBytesRead)*1.0)/(1024*1024)
-          println(("%s, %d, %.4f, %.4f, %d, %.4f").format(config.dateFormat.format(reportTime), config.fetchSize,
+          println("%s, %d, %.4f, %.4f, %d, %.4f".format(config.dateFormat.format(reportTime), config.fetchSize,
             (totalBytesRead*1.0)/(1024*1024), totalMBRead/elapsed,
             totalMessagesRead, (totalMessagesRead-lastMessagesRead)/elapsed))
         }
@@ -107,7 +107,7 @@ object SimpleConsumerPerformance {
 
     if(!config.showDetailedStats) {
       val totalMBRead = (totalBytesRead*1.0)/(1024*1024)
-      println(("%s, %s, %d, %.4f, %.4f, %d, %.4f").format(config.dateFormat.format(startMs),
+      println("%s, %s, %d, %.4f, %.4f, %d, %.4f".format(config.dateFormat.format(startMs),
         config.dateFormat.format(reportTime), config.fetchSize, totalMBRead, totalMBRead/elapsed,
         totalMessagesRead, totalMessagesRead/elapsed))
     }
diff --git a/core/src/main/scala/kafka/tools/SimpleConsumerShell.scala b/core/src/main/scala/kafka/tools/SimpleConsumerShell.scala
index 6ad68b62bbd45..c975d24e5ce0e 100755
--- a/core/src/main/scala/kafka/tools/SimpleConsumerShell.scala
+++ b/core/src/main/scala/kafka/tools/SimpleConsumerShell.scala
@@ -131,15 +131,15 @@ object SimpleConsumerShell extends Logging {
     ToolsUtils.validatePortOrDie(parser,brokerList)
     val metadataTargetBrokers = ClientUtils.parseBrokerList(brokerList)
     val topicsMetadata = ClientUtils.fetchTopicMetadata(Set(topic), metadataTargetBrokers, clientId, maxWaitMs).topicsMetadata
-    if(topicsMetadata.size != 1 || !topicsMetadata(0).topic.equals(topic)) {
+    if(topicsMetadata.size != 1 || !topicsMetadata.head.topic.equals(topic)) {
       System.err.println(("Error: no valid topic metadata for topic: %s, " + "what we get from server is only: %s").format(topic, topicsMetadata))
       System.exit(1)
     }
 
     // validating partition id
-    val partitionsMetadata = topicsMetadata(0).partitionsMetadata
+    val partitionsMetadata = topicsMetadata.head.partitionsMetadata
     val partitionMetadataOpt = partitionsMetadata.find(p => p.partitionId == partitionId)
-    if (!partitionMetadataOpt.isDefined) {
+    if (partitionMetadataOpt.isEmpty) {
       System.err.println("Error: partition %d does not exist for topic %s".format(partitionId, topic))
       System.exit(1)
     }
@@ -149,7 +149,7 @@ object SimpleConsumerShell extends Logging {
     var replicaOpt: Option[BrokerEndPoint] = null
     if (replicaId == UseLeaderReplica) {
       replicaOpt = partitionMetadataOpt.get.leader
-      if (!replicaOpt.isDefined) {
+      if (replicaOpt.isEmpty) {
         System.err.println("Error: user specifies to fetch from leader for partition (%s, %d) which has not been elected yet".format(topic, partitionId))
         System.exit(1)
       }
@@ -157,7 +157,7 @@ object SimpleConsumerShell extends Logging {
     else {
       val replicasForPartition = partitionMetadataOpt.get.replicas
       replicaOpt = replicasForPartition.find(r => r.id == replicaId)
-      if(!replicaOpt.isDefined) {
+      if(replicaOpt.isEmpty) {
         System.err.println("Error: replica %d does not exist for partition (%s, %d)".format(replicaId, topic, partitionId))
         System.exit(1)
       }
diff --git a/core/src/main/scala/kafka/tools/StateChangeLogMerger.scala b/core/src/main/scala/kafka/tools/StateChangeLogMerger.scala
index 8b523e7518fde..1f148defa3258 100755
--- a/core/src/main/scala/kafka/tools/StateChangeLogMerger.scala
+++ b/core/src/main/scala/kafka/tools/StateChangeLogMerger.scala
@@ -108,7 +108,7 @@ object StateChangeLogMerger extends Logging {
       val fileNameIndex = regex.lastIndexOf('/') + 1
       val dirName = if (fileNameIndex == 0) "." else regex.substring(0, fileNameIndex - 1)
       val fileNameRegex = new Regex(regex.substring(fileNameIndex))
-      files :::= new java.io.File(dirName).listFiles.filter(f => fileNameRegex.findFirstIn(f.getName) != None).map(dirName + "/" + _.getName).toList
+      files :::= new java.io.File(dirName).listFiles.filter(f => fileNameRegex.findFirstIn(f.getName).isDefined).map(dirName + "/" + _.getName).toList
     }
     if (options.has(topicOpt)) {
       topic = options.valueOf(topicOpt)
@@ -141,9 +141,9 @@ object StateChangeLogMerger extends Logging {
       if (!lineItr.isEmpty)
         lines ::= lineItr
     }
-    if (!lines.isEmpty) pqueue.enqueue(lines:_*)
+    if (lines.nonEmpty) pqueue.enqueue(lines:_*)
 
-    while (!pqueue.isEmpty) {
+    while (pqueue.nonEmpty) {
       val lineItr = pqueue.dequeue()
       output.write((lineItr.line + "\n").getBytes)
       val nextLineItr = getNextLine(lineItr.itr)
@@ -182,7 +182,7 @@ object StateChangeLogMerger extends Logging {
 
   class LineIterator(val line: String, val itr: Iterator[String]) {
     def this() = this("", null)
-    def isEmpty = (line == "" && itr == null)
+    def isEmpty = line == "" && itr == null
   }
 
   implicit object dateBasedOrdering extends Ordering[LineIterator] {
diff --git a/core/src/main/scala/kafka/tools/VerifyConsumerRebalance.scala b/core/src/main/scala/kafka/tools/VerifyConsumerRebalance.scala
index 3077896483645..5f3940270c353 100644
--- a/core/src/main/scala/kafka/tools/VerifyConsumerRebalance.scala
+++ b/core/src/main/scala/kafka/tools/VerifyConsumerRebalance.scala
@@ -89,7 +89,7 @@ object VerifyConsumerRebalance extends Logging {
       info("Alive partitions for topic %s are %s ".format(topic, partitions.toString))
       info("Alive consumers for topic %s => %s ".format(topic, consumersPerTopicMap.get(topic)))
       val partitionsWithOwners = zkUtils.getChildrenParentMayNotExist(topicDirs.consumerOwnerDir)
-      if(partitionsWithOwners.size == 0) {
+      if(partitionsWithOwners.isEmpty) {
         error("No owners for any partitions for topic " + topic)
         rebalanceSucceeded = false
       }
diff --git a/core/src/main/scala/kafka/utils/CoreUtils.scala b/core/src/main/scala/kafka/utils/CoreUtils.scala
index 5b6c59f48f320..21658d39ea3e2 100755
--- a/core/src/main/scala/kafka/utils/CoreUtils.scala
+++ b/core/src/main/scala/kafka/utils/CoreUtils.scala
@@ -258,7 +258,7 @@ object CoreUtils extends Logging {
        * Per RFC4627, section 2.5, we're not technically required to
        * encode the C1 codes, but we do to be safe.
        */
-      case c if ((c >= '\u0000' && c <= '\u001f') || (c >= '\u007f' && c <= '\u009f')) => "\\u%04x".format(c: Int)
+      case c if (c >= '\u0000' && c <= '\u001f') || (c >= '\u007f' && c <= '\u009f') => "\\u%04x".format(c: Int)
       case c => c
     }.mkString
   }
@@ -269,7 +269,7 @@ object CoreUtils extends Logging {
   def duplicates[T](s: Traversable[T]): Iterable[T] = {
     s.groupBy(identity)
       .map{ case (k,l) => (k,l.size)}
-      .filter{ case (k,l) => (l > 1) }
+      .filter{ case (k,l) => l > 1 }
       .keys
   }
 
diff --git a/core/src/main/scala/kafka/utils/ToolsUtils.scala b/core/src/main/scala/kafka/utils/ToolsUtils.scala
index fef93929ea03e..65758d85113cb 100644
--- a/core/src/main/scala/kafka/utils/ToolsUtils.scala
+++ b/core/src/main/scala/kafka/utils/ToolsUtils.scala
@@ -29,7 +29,7 @@ object ToolsUtils {
       hostPortData =>
         org.apache.kafka.common.utils.Utils.getPort(hostPortData) != null
     }
-    val isValid = !(validHostPort.isEmpty) && validHostPort.size == hostPorts.length
+    val isValid = !validHostPort.isEmpty && validHostPort.size == hostPorts.length
     if(!isValid)
       CommandLineUtils.printUsageAndDie(parser, "Please provide valid host:port like host1:9091,host2:9092\n ")
   }
diff --git a/core/src/main/scala/kafka/utils/VerifiableProperties.scala b/core/src/main/scala/kafka/utils/VerifiableProperties.scala
index 34cab87034254..f57245f859bdd 100755
--- a/core/src/main/scala/kafka/utils/VerifiableProperties.scala
+++ b/core/src/main/scala/kafka/utils/VerifiableProperties.scala
@@ -227,6 +227,6 @@ class VerifiableProperties(val props: Properties) extends Logging {
     }
   }
   
-  override def toString(): String = props.toString
+  override def toString: String = props.toString
  
 }
diff --git a/core/src/main/scala/kafka/utils/ZkUtils.scala b/core/src/main/scala/kafka/utils/ZkUtils.scala
index 1278a707c3b8e..f02ab20a2319b 100644
--- a/core/src/main/scala/kafka/utils/ZkUtils.scala
+++ b/core/src/main/scala/kafka/utils/ZkUtils.scala
@@ -653,7 +653,7 @@ class ZkUtils(val zkClient: ZkClient,
       val topic = topicAndPartitionMap._1
       val partitionMap = topicAndPartitionMap._2
       debug("partition assignment of /brokers/topics/%s is %s".format(topic, partitionMap))
-      (topic -> partitionMap.keys.toSeq.sortWith((s,t) => s < t))
+      topic -> partitionMap.keys.toSeq.sortWith((s, t) => s < t)
     }
   }
 
@@ -663,7 +663,7 @@ class ZkUtils(val zkClient: ZkClient,
     jsonPartitionMapOpt match {
       case Some(jsonPartitionMap) =>
         val reassignedPartitions = parsePartitionReassignmentData(jsonPartitionMap)
-        reassignedPartitions.map(p => (p._1 -> new ReassignedPartitionsContext(p._2)))
+        reassignedPartitions.map(p => p._1 -> new ReassignedPartitionsContext(p._2))
       case None => Map.empty[TopicAndPartition, ReassignedPartitionsContext]
     }
   }
@@ -828,9 +828,9 @@ class ZkUtils(val zkClient: ZkClient,
     val topics = getChildrenParentMayNotExist(BrokerTopicsPath)
     if(topics == null) Set.empty[TopicAndPartition]
     else {
-      topics.map { topic =>
+      topics.flatMap { topic =>
         getChildren(getTopicPartitionsPath(topic)).map(_.toInt).map(TopicAndPartition(topic, _))
-      }.flatten.toSet
+      }.toSet
     }
   }
 
diff --git a/core/src/test/scala/integration/kafka/api/AdminClientTest.scala b/core/src/test/scala/integration/kafka/api/AdminClientTest.scala
index 3d39475d3d074..891a72cb402a6 100644
--- a/core/src/test/scala/integration/kafka/api/AdminClientTest.scala
+++ b/core/src/test/scala/integration/kafka/api/AdminClientTest.scala
@@ -63,25 +63,25 @@ class AdminClientTest extends IntegrationTestHarness with Logging {
 
   @Test
   def testListGroups() {
-    consumers(0).subscribe(List(topic))
+    consumers.head.subscribe(List(topic))
     TestUtils.waitUntilTrue(() => {
-      consumers(0).poll(0)
-      !consumers(0).assignment().isEmpty
+      consumers.head.poll(0)
+      !consumers.head.assignment().isEmpty
     }, "Expected non-empty assignment")
 
     val groups = client.listAllGroupsFlattened
     assertFalse(groups.isEmpty)
-    val group = groups(0)
+    val group = groups.head
     assertEquals(groupId, group.groupId)
     assertEquals("consumer", group.protocolType)
   }
 
   @Test
   def testDescribeGroup() {
-    consumers(0).subscribe(List(topic))
+    consumers.head.subscribe(List(topic))
     TestUtils.waitUntilTrue(() => {
-      consumers(0).poll(0)
-      !consumers(0).assignment().isEmpty
+      consumers.head.poll(0)
+      !consumers.head.assignment().isEmpty
     }, "Expected non-empty assignment")
 
     val group = client.describeGroup(groupId)
@@ -90,7 +90,7 @@ class AdminClientTest extends IntegrationTestHarness with Logging {
     assertEquals("Stable", group.state)
     assertFalse(group.members.isEmpty)
 
-    val member = group.members(0)
+    val member = group.members.head
     assertEquals(clientId, member.clientId)
     assertFalse(member.clientHost.isEmpty)
     assertFalse(member.memberId.isEmpty)
@@ -98,10 +98,10 @@ class AdminClientTest extends IntegrationTestHarness with Logging {
 
   @Test
   def testDescribeConsumerGroup() {
-    consumers(0).subscribe(List(topic))
+    consumers.head.subscribe(List(topic))
     TestUtils.waitUntilTrue(() => {
-      consumers(0).poll(0)
-      !consumers(0).assignment().isEmpty
+      consumers.head.poll(0)
+      !consumers.head.assignment().isEmpty
     }, "Expected non-empty assignment")
 
     val consumerSummaries = client.describeConsumerGroup(groupId)
diff --git a/core/src/test/scala/integration/kafka/api/AuthorizerIntegrationTest.scala b/core/src/test/scala/integration/kafka/api/AuthorizerIntegrationTest.scala
index 2d5900f8364a7..10e0baed74755 100644
--- a/core/src/test/scala/integration/kafka/api/AuthorizerIntegrationTest.scala
+++ b/core/src/test/scala/integration/kafka/api/AuthorizerIntegrationTest.scala
@@ -413,8 +413,8 @@ class AuthorizerIntegrationTest extends KafkaServerTestHarness {
     addAndVerifyAcls(GroupReadAcl(groupResource), groupResource)
     addAndVerifyAcls(ClusterAcl(Resource.ClusterResource), Resource.ClusterResource)
     try {
-      this.consumers(0).assign(List(topicPartition).asJava)
-      consumeRecords(this.consumers(0))
+      this.consumers.head.assign(List(topicPartition).asJava)
+      consumeRecords(this.consumers.head)
       Assert.fail("should have thrown exception")
     } catch {
       case e: TopicAuthorizationException =>
@@ -425,7 +425,7 @@ class AuthorizerIntegrationTest extends KafkaServerTestHarness {
     addAndVerifyAcls(Set(new Acl(KafkaPrincipal.ANONYMOUS, Allow, Acl.WildCardHost, Create)), Resource.ClusterResource)
 
     sendRecords(numRecords, topicPartition)
-    consumeRecords(this.consumers(0), topic = newTopic, part = 0)
+    consumeRecords(this.consumers.head, topic = newTopic, part = 0)
   }
 
   @Test(expected = classOf[AuthorizationException])
@@ -505,7 +505,7 @@ class AuthorizerIntegrationTest extends KafkaServerTestHarness {
   @Test
   def testListOffsetsWithNoTopicAccess() {
     val e = intercept[TopicAuthorizationException] {
-      this.consumers.head.partitionsFor(topic);
+      this.consumers.head.partitionsFor(topic)
     }
     assertEquals(Set(topic), e.unauthorizedTopics().asScala)
   }
@@ -513,7 +513,7 @@ class AuthorizerIntegrationTest extends KafkaServerTestHarness {
   @Test
   def testListOfsetsWithTopicDescribe() {
     addAndVerifyAcls(Set(new Acl(KafkaPrincipal.ANONYMOUS, Allow, Acl.WildCardHost, Describe)), topicResource)
-    this.consumers.head.partitionsFor(topic);
+    this.consumers.head.partitionsFor(topic)
   }
 
   def removeAllAcls() = {
diff --git a/core/src/test/scala/integration/kafka/api/BaseConsumerTest.scala b/core/src/test/scala/integration/kafka/api/BaseConsumerTest.scala
index 23fcfa61570a1..ea74d5dc9b4b1 100644
--- a/core/src/test/scala/integration/kafka/api/BaseConsumerTest.scala
+++ b/core/src/test/scala/integration/kafka/api/BaseConsumerTest.scala
@@ -68,17 +68,17 @@ abstract class BaseConsumerTest extends IntegrationTestHarness with Logging {
     val numRecords = 10000
     sendRecords(numRecords)
 
-    assertEquals(0, this.consumers(0).assignment.size)
-    this.consumers(0).assign(List(tp).asJava)
-    assertEquals(1, this.consumers(0).assignment.size)
+    assertEquals(0, this.consumers.head.assignment.size)
+    this.consumers.head.assign(List(tp).asJava)
+    assertEquals(1, this.consumers.head.assignment.size)
 
-    this.consumers(0).seek(tp, 0)
-    consumeAndVerifyRecords(consumer = this.consumers(0), numRecords = numRecords, startingOffset = 0)
+    this.consumers.head.seek(tp, 0)
+    consumeAndVerifyRecords(consumer = this.consumers.head, numRecords = numRecords, startingOffset = 0)
 
     // check async commit callbacks
     val commitCallback = new CountConsumerCommitCallback()
-    this.consumers(0).commitAsync(commitCallback)
-    awaitCommitCallback(this.consumers(0), commitCallback)
+    this.consumers.head.commitAsync(commitCallback)
+    awaitCommitCallback(this.consumers.head, commitCallback)
   }
 
   @Test
@@ -132,28 +132,28 @@ abstract class BaseConsumerTest extends IntegrationTestHarness with Logging {
     sendRecords(5, tp)
     sendRecords(7, tp2)
 
-    this.consumers(0).assign(List(tp, tp2).asJava)
+    this.consumers.head.assign(List(tp, tp2).asJava)
 
     // Need to poll to join the group
-    this.consumers(0).poll(50)
-    val pos1 = this.consumers(0).position(tp)
-    val pos2 = this.consumers(0).position(tp2)
-    this.consumers(0).commitSync(Map[TopicPartition, OffsetAndMetadata]((tp, new OffsetAndMetadata(3L))).asJava)
-    assertEquals(3, this.consumers(0).committed(tp).offset)
-    assertNull(this.consumers(0).committed(tp2))
+    this.consumers.head.poll(50)
+    val pos1 = this.consumers.head.position(tp)
+    val pos2 = this.consumers.head.position(tp2)
+    this.consumers.head.commitSync(Map[TopicPartition, OffsetAndMetadata]((tp, new OffsetAndMetadata(3L))).asJava)
+    assertEquals(3, this.consumers.head.committed(tp).offset)
+    assertNull(this.consumers.head.committed(tp2))
 
     // Positions should not change
-    assertEquals(pos1, this.consumers(0).position(tp))
-    assertEquals(pos2, this.consumers(0).position(tp2))
-    this.consumers(0).commitSync(Map[TopicPartition, OffsetAndMetadata]((tp2, new OffsetAndMetadata(5L))).asJava)
-    assertEquals(3, this.consumers(0).committed(tp).offset)
-    assertEquals(5, this.consumers(0).committed(tp2).offset)
+    assertEquals(pos1, this.consumers.head.position(tp))
+    assertEquals(pos2, this.consumers.head.position(tp2))
+    this.consumers.head.commitSync(Map[TopicPartition, OffsetAndMetadata]((tp2, new OffsetAndMetadata(5L))).asJava)
+    assertEquals(3, this.consumers.head.committed(tp).offset)
+    assertEquals(5, this.consumers.head.committed(tp2).offset)
 
     // Using async should pick up the committed changes after commit completes
     val commitCallback = new CountConsumerCommitCallback()
-    this.consumers(0).commitAsync(Map[TopicPartition, OffsetAndMetadata]((tp2, new OffsetAndMetadata(7L))).asJava, commitCallback)
-    awaitCommitCallback(this.consumers(0), commitCallback)
-    assertEquals(7, this.consumers(0).committed(tp2).offset)
+    this.consumers.head.commitAsync(Map[TopicPartition, OffsetAndMetadata]((tp2, new OffsetAndMetadata(7L))).asJava, commitCallback)
+    awaitCommitCallback(this.consumers.head, commitCallback)
+    assertEquals(7, this.consumers.head.committed(tp2).offset)
   }
 
   @Test
@@ -194,10 +194,10 @@ abstract class BaseConsumerTest extends IntegrationTestHarness with Logging {
     while (parts == null)
       parts = consumer0.partitionsFor(TopicConstants.GROUP_METADATA_TOPIC_NAME).asScala
     assertEquals(1, parts.size)
-    assertNotNull(parts(0).leader())
+    assertNotNull(parts.head.leader())
 
     // shutdown the coordinator
-    val coordinator = parts(0).leader().id()
+    val coordinator = parts.head.leader().id()
     this.servers(coordinator).shutdown()
 
     // this should cause another callback execution
@@ -269,7 +269,7 @@ abstract class BaseConsumerTest extends IntegrationTestHarness with Logging {
   }
 
   protected def sendRecords(numRecords: Int, tp: TopicPartition) {
-    sendRecords(this.producers(0), numRecords, tp)
+    sendRecords(this.producers.head, numRecords, tp)
   }
 
   protected def sendRecords(producer: KafkaProducer[Array[Byte], Array[Byte]], numRecords: Int, tp: TopicPartition) {
@@ -416,7 +416,7 @@ abstract class BaseConsumerTest extends IntegrationTestHarness with Logging {
    */
   def isPartitionAssignmentValid(assignments: Buffer[Set[TopicPartition]],
                                  partitions: Set[TopicPartition]): Boolean = {
-    val allNonEmptyAssignments = assignments forall (assignment => assignment.size > 0)
+    val allNonEmptyAssignments = assignments forall (assignment => assignment.nonEmpty)
     if (!allNonEmptyAssignments) {
       // at least one consumer got empty assignment
       return false
diff --git a/core/src/test/scala/integration/kafka/api/BaseProducerSendTest.scala b/core/src/test/scala/integration/kafka/api/BaseProducerSendTest.scala
index 0a2b49ad75a02..8eaf8279cdc91 100644
--- a/core/src/test/scala/integration/kafka/api/BaseProducerSendTest.scala
+++ b/core/src/test/scala/integration/kafka/api/BaseProducerSendTest.scala
@@ -56,7 +56,7 @@ abstract class BaseProducerSendTest extends KafkaServerTestHarness {
     super.setUp()
 
     // TODO: we need to migrate to new consumers when 0.9 is final
-    consumer1 = new SimpleConsumer("localhost", servers(0).boundPort(), 100, 1024 * 1024, "")
+    consumer1 = new SimpleConsumer("localhost", servers.head.boundPort(), 100, 1024 * 1024, "")
     consumer2 = new SimpleConsumer("localhost", servers(1).boundPort(), 100, 1024 * 1024, "")
   }
 
@@ -298,7 +298,7 @@ abstract class BaseProducerSendTest extends KafkaServerTestHarness {
       }
 
       // make sure the fetched messages also respect the partitioning and ordering
-      val fetchResponse1 = if (leader1.get == configs(0).brokerId) {
+      val fetchResponse1 = if (leader1.get == configs.head.brokerId) {
         consumer1.fetch(new FetchRequestBuilder().addFetch(topic, partition, 0, Int.MaxValue).build())
       } else {
         consumer2.fetch(new FetchRequestBuilder().addFetch(topic, partition, 0, Int.MaxValue).build())
@@ -307,7 +307,7 @@ abstract class BaseProducerSendTest extends KafkaServerTestHarness {
       assertEquals("Should have fetched " + numRecords + " messages", numRecords, messageSet1.size)
 
       // TODO: also check topic and partition after they are added in the return messageSet
-      for (i <- 0 to numRecords - 1) {
+      for (i <- 0 until numRecords) {
         assertEquals(new Message(bytes = ("value" + (i + 1)).getBytes, now, Message.MagicValue_V1), messageSet1(i).message)
         assertEquals(i.toLong, messageSet1(i).offset)
       }
@@ -386,7 +386,7 @@ abstract class BaseProducerSendTest extends KafkaServerTestHarness {
             assertEquals("java.lang.IllegalStateException: Producer is closed forcefully.", e.getMessage)
         }
       }
-      val fetchResponse = if (leader0.get == configs(0).brokerId) {
+      val fetchResponse = if (leader0.get == configs.head.brokerId) {
         consumer1.fetch(new FetchRequestBuilder().addFetch(topic, 0, 0, Int.MaxValue).build())
       } else {
         consumer2.fetch(new FetchRequestBuilder().addFetch(topic, 0, 0, Int.MaxValue).build())
@@ -423,13 +423,13 @@ abstract class BaseProducerSendTest extends KafkaServerTestHarness {
       val producer = createProducer(brokerList, lingerMs = Long.MaxValue)
       try {
         // send message to partition 0
-        val responses = ((0 until numRecords) map (i => producer.send(record, new CloseCallback(producer))))
+        val responses = (0 until numRecords) map (i => producer.send(record, new CloseCallback(producer)))
         assertTrue("No request is complete.", responses.forall(!_.isDone()))
         // flush the messages.
         producer.flush()
         assertTrue("All request are complete.", responses.forall(_.isDone()))
         // Check the messages received by broker.
-        val fetchResponse = if (leader.get == configs(0).brokerId) {
+        val fetchResponse = if (leader.get == configs.head.brokerId) {
           consumer1.fetch(new FetchRequestBuilder().addFetch(topic, 0, 0, Int.MaxValue).build())
         } else {
           consumer2.fetch(new FetchRequestBuilder().addFetch(topic, 0, 0, Int.MaxValue).build())
@@ -446,7 +446,7 @@ abstract class BaseProducerSendTest extends KafkaServerTestHarness {
   @Test
   def testSendWithInvalidCreateTime() {
     val topicProps = new Properties()
-    topicProps.setProperty(LogConfig.MessageTimestampDifferenceMaxMsProp, "1000");
+    topicProps.setProperty(LogConfig.MessageTimestampDifferenceMaxMsProp, "1000")
     TestUtils.createTopic(zkUtils, topic, 1, 2, servers, topicProps)
 
     val producer = createProducer(brokerList = brokerList)
diff --git a/core/src/test/scala/integration/kafka/api/ConsumerBounceTest.scala b/core/src/test/scala/integration/kafka/api/ConsumerBounceTest.scala
index 84243403cb617..c76a216d75135 100644
--- a/core/src/test/scala/integration/kafka/api/ConsumerBounceTest.scala
+++ b/core/src/test/scala/integration/kafka/api/ConsumerBounceTest.scala
@@ -79,7 +79,7 @@ class ConsumerBounceTest extends IntegrationTestHarness with Logging {
     this.producers.foreach(_.close)
 
     var consumed = 0L
-    val consumer = this.consumers(0)
+    val consumer = this.consumers.head
 
     consumer.subscribe(List(topic), new ConsumerRebalanceListener {
       override def onPartitionsAssigned(partitions: util.Collection[TopicPartition]) {
@@ -124,7 +124,7 @@ class ConsumerBounceTest extends IntegrationTestHarness with Logging {
     sendRecords(numRecords)
     this.producers.foreach(_.close)
 
-    val consumer = this.consumers(0)
+    val consumer = this.consumers.head
     consumer.assign(List(tp))
     consumer.seek(tp, 0)
 
@@ -174,7 +174,7 @@ class ConsumerBounceTest extends IntegrationTestHarness with Logging {
 
   private def sendRecords(numRecords: Int) {
     val futures = (0 until numRecords).map { i =>
-      this.producers(0).send(new ProducerRecord(topic, part, i.toString.getBytes, i.toString.getBytes))
+      this.producers.head.send(new ProducerRecord(topic, part, i.toString.getBytes, i.toString.getBytes))
     }
     futures.map(_.get)
   }
diff --git a/core/src/test/scala/integration/kafka/api/IntegrationTestHarness.scala b/core/src/test/scala/integration/kafka/api/IntegrationTestHarness.scala
index 6e76f90b21a32..29d3bd6eba16b 100644
--- a/core/src/test/scala/integration/kafka/api/IntegrationTestHarness.scala
+++ b/core/src/test/scala/integration/kafka/api/IntegrationTestHarness.scala
@@ -81,7 +81,7 @@ trait IntegrationTestHarness extends KafkaServerTestHarness {
       serverConfig.getProperty(KafkaConfig.OffsetsTopicPartitionsProp).toInt,
       serverConfig.getProperty(KafkaConfig.OffsetsTopicReplicationFactorProp).toInt,
       servers,
-      servers(0).groupCoordinator.offsetsTopicConfigs)
+      servers.head.groupCoordinator.offsetsTopicConfigs)
   }
 
   @After
diff --git a/core/src/test/scala/integration/kafka/api/PlaintextConsumerTest.scala b/core/src/test/scala/integration/kafka/api/PlaintextConsumerTest.scala
index b22ccde9ed313..a5a6cd6fd825a 100644
--- a/core/src/test/scala/integration/kafka/api/PlaintextConsumerTest.scala
+++ b/core/src/test/scala/integration/kafka/api/PlaintextConsumerTest.scala
@@ -79,8 +79,8 @@ class PlaintextConsumerTest extends BaseConsumerTest {
     consumer0.close()
 
     // now we should see the committed positions from another consumer
-    assertEquals(300, this.consumers(0).committed(tp).offset)
-    assertEquals(500, this.consumers(0).committed(tp2).offset)
+    assertEquals(300, this.consumers.head.committed(tp).offset)
+    assertEquals(500, this.consumers.head.committed(tp2).offset)
   }
 
   @Test
@@ -109,22 +109,22 @@ class PlaintextConsumerTest extends BaseConsumerTest {
     consumer0.close()
 
     // now we should see the committed positions from another consumer
-    assertEquals(300, this.consumers(0).committed(tp).offset)
-    assertEquals(500, this.consumers(0).committed(tp2).offset)
+    assertEquals(300, this.consumers.head.committed(tp).offset)
+    assertEquals(500, this.consumers.head.committed(tp2).offset)
   }
 
   @Test
   def testAutoOffsetReset() {
     sendRecords(1)
-    this.consumers(0).assign(List(tp).asJava)
-    consumeAndVerifyRecords(consumer = this.consumers(0), numRecords = 1, startingOffset = 0)
+    this.consumers.head.assign(List(tp).asJava)
+    consumeAndVerifyRecords(consumer = this.consumers.head, numRecords = 1, startingOffset = 0)
   }
 
   @Test
   def testGroupConsumption() {
     sendRecords(10)
-    this.consumers(0).subscribe(List(topic).asJava)
-    consumeAndVerifyRecords(consumer = this.consumers(0), numRecords = 1, startingOffset = 0)
+    this.consumers.head.subscribe(List(topic).asJava)
+    consumeAndVerifyRecords(consumer = this.consumers.head, numRecords = 1, startingOffset = 0)
   }
 
   @Test
@@ -147,11 +147,11 @@ class PlaintextConsumerTest extends BaseConsumerTest {
     sendRecords(1000, new TopicPartition(topic3, 0))
     sendRecords(1000, new TopicPartition(topic3, 1))
 
-    assertEquals(0, this.consumers(0).assignment().size)
+    assertEquals(0, this.consumers.head.assignment().size)
 
     val pattern = Pattern.compile("t.*c")
-    this.consumers(0).subscribe(pattern, new TestConsumerReassignmentListener)
-    this.consumers(0).poll(50)
+    this.consumers.head.subscribe(pattern, new TestConsumerReassignmentListener)
+    this.consumers.head.poll(50)
 
     var subscriptions = Set(
       new TopicPartition(topic, 0),
@@ -160,9 +160,9 @@ class PlaintextConsumerTest extends BaseConsumerTest {
       new TopicPartition(topic1, 1))
 
     TestUtils.waitUntilTrue(() => {
-      this.consumers(0).poll(50)
-      this.consumers(0).assignment() == subscriptions.asJava
-    }, s"Expected partitions ${subscriptions.asJava} but actually got ${this.consumers(0).assignment()}")
+      this.consumers.head.poll(50)
+      this.consumers.head.assignment() == subscriptions.asJava
+    }, s"Expected partitions ${subscriptions.asJava} but actually got ${this.consumers.head.assignment()}")
 
     val topic4 = "tsomec" // matches subscribed pattern
     TestUtils.createTopic(this.zkUtils, topic4, 2, serverCount, this.servers)
@@ -175,12 +175,12 @@ class PlaintextConsumerTest extends BaseConsumerTest {
 
 
     TestUtils.waitUntilTrue(() => {
-      this.consumers(0).poll(50)
-      this.consumers(0).assignment() == subscriptions.asJava
-    }, s"Expected partitions ${subscriptions.asJava} but actually got ${this.consumers(0).assignment()}")
+      this.consumers.head.poll(50)
+      this.consumers.head.assignment() == subscriptions.asJava
+    }, s"Expected partitions ${subscriptions.asJava} but actually got ${this.consumers.head.assignment()}")
 
-    this.consumers(0).unsubscribe()
-    assertEquals(0, this.consumers(0).assignment().size)
+    this.consumers.head.unsubscribe()
+    assertEquals(0, this.consumers.head.assignment().size)
   }
 
   @Test
@@ -193,10 +193,10 @@ class PlaintextConsumerTest extends BaseConsumerTest {
     sendRecords(1000, new TopicPartition(topic1, 0))
     sendRecords(1000, new TopicPartition(topic1, 1))
 
-    assertEquals(0, this.consumers(0).assignment().size)
+    assertEquals(0, this.consumers.head.assignment().size)
 
-    this.consumers(0).subscribe(Pattern.compile("t.*c"), new TestConsumerReassignmentListener)
-    this.consumers(0).poll(50)
+    this.consumers.head.subscribe(Pattern.compile("t.*c"), new TestConsumerReassignmentListener)
+    this.consumers.head.poll(50)
 
     val subscriptions = Set(
       new TopicPartition(topic, 0),
@@ -205,39 +205,39 @@ class PlaintextConsumerTest extends BaseConsumerTest {
       new TopicPartition(topic1, 1))
 
     TestUtils.waitUntilTrue(() => {
-      this.consumers(0).poll(50)
-      this.consumers(0).assignment() == subscriptions.asJava
-    }, s"Expected partitions ${subscriptions.asJava} but actually got ${this.consumers(0).assignment()}")
+      this.consumers.head.poll(50)
+      this.consumers.head.assignment() == subscriptions.asJava
+    }, s"Expected partitions ${subscriptions.asJava} but actually got ${this.consumers.head.assignment()}")
 
-    this.consumers(0).unsubscribe()
-    assertEquals(0, this.consumers(0).assignment().size)
+    this.consumers.head.unsubscribe()
+    assertEquals(0, this.consumers.head.assignment().size)
   }
 
   @Test
   def testCommitMetadata() {
-    this.consumers(0).assign(List(tp).asJava)
+    this.consumers.head.assign(List(tp).asJava)
 
     // sync commit
     val syncMetadata = new OffsetAndMetadata(5, "foo")
-    this.consumers(0).commitSync(Map((tp, syncMetadata)).asJava)
-    assertEquals(syncMetadata, this.consumers(0).committed(tp))
+    this.consumers.head.commitSync(Map((tp, syncMetadata)).asJava)
+    assertEquals(syncMetadata, this.consumers.head.committed(tp))
 
     // async commit
     val asyncMetadata = new OffsetAndMetadata(10, "bar")
     val callback = new CountConsumerCommitCallback
-    this.consumers(0).commitAsync(Map((tp, asyncMetadata)).asJava, callback)
-    awaitCommitCallback(this.consumers(0), callback)
-    assertEquals(asyncMetadata, this.consumers(0).committed(tp))
+    this.consumers.head.commitAsync(Map((tp, asyncMetadata)).asJava, callback)
+    awaitCommitCallback(this.consumers.head, callback)
+    assertEquals(asyncMetadata, this.consumers.head.committed(tp))
 
     // handle null metadata
     val nullMetadata = new OffsetAndMetadata(5, null)
-    this.consumers(0).commitSync(Map((tp, nullMetadata)).asJava)
-    assertEquals(nullMetadata, this.consumers(0).committed(tp))
+    this.consumers.head.commitSync(Map((tp, nullMetadata)).asJava)
+    assertEquals(nullMetadata, this.consumers.head.committed(tp))
   }
 
   @Test
   def testAsyncCommit() {
-    val consumer = this.consumers(0)
+    val consumer = this.consumers.head
     consumer.assign(List(tp).asJava)
     consumer.poll(0)
 
@@ -255,18 +255,18 @@ class PlaintextConsumerTest extends BaseConsumerTest {
     val otherTopic = "other"
     val subscriptions = Set(new TopicPartition(topic, 0), new TopicPartition(topic, 1))
     val expandedSubscriptions = subscriptions ++ Set(new TopicPartition(otherTopic, 0), new TopicPartition(otherTopic, 1))
-    this.consumers(0).subscribe(List(topic).asJava)
+    this.consumers.head.subscribe(List(topic).asJava)
     TestUtils.waitUntilTrue(() => {
-      this.consumers(0).poll(50)
-      this.consumers(0).assignment == subscriptions.asJava
-    }, s"Expected partitions ${subscriptions.asJava} but actually got ${this.consumers(0).assignment}")
+      this.consumers.head.poll(50)
+      this.consumers.head.assignment == subscriptions.asJava
+    }, s"Expected partitions ${subscriptions.asJava} but actually got ${this.consumers.head.assignment}")
 
     TestUtils.createTopic(this.zkUtils, otherTopic, 2, serverCount, this.servers)
-    this.consumers(0).subscribe(List(topic, otherTopic).asJava)
+    this.consumers.head.subscribe(List(topic, otherTopic).asJava)
     TestUtils.waitUntilTrue(() => {
-      this.consumers(0).poll(50)
-      this.consumers(0).assignment == expandedSubscriptions.asJava
-    }, s"Expected partitions ${expandedSubscriptions.asJava} but actually got ${this.consumers(0).assignment}")
+      this.consumers.head.poll(50)
+      this.consumers.head.assignment == expandedSubscriptions.asJava
+    }, s"Expected partitions ${expandedSubscriptions.asJava} but actually got ${this.consumers.head.assignment}")
   }
 
   @Test
@@ -275,42 +275,42 @@ class PlaintextConsumerTest extends BaseConsumerTest {
     TestUtils.createTopic(this.zkUtils, otherTopic, 2, serverCount, this.servers)
     val subscriptions = Set(new TopicPartition(topic, 0), new TopicPartition(topic, 1), new TopicPartition(otherTopic, 0), new TopicPartition(otherTopic, 1))
     val shrunkenSubscriptions = Set(new TopicPartition(topic, 0), new TopicPartition(topic, 1))
-    this.consumers(0).subscribe(List(topic, otherTopic).asJava)
+    this.consumers.head.subscribe(List(topic, otherTopic).asJava)
     TestUtils.waitUntilTrue(() => {
-      this.consumers(0).poll(50)
-      this.consumers(0).assignment == subscriptions.asJava
-    }, s"Expected partitions ${subscriptions.asJava} but actually got ${this.consumers(0).assignment}")
+      this.consumers.head.poll(50)
+      this.consumers.head.assignment == subscriptions.asJava
+    }, s"Expected partitions ${subscriptions.asJava} but actually got ${this.consumers.head.assignment}")
 
-    this.consumers(0).subscribe(List(topic).asJava)
+    this.consumers.head.subscribe(List(topic).asJava)
     TestUtils.waitUntilTrue(() => {
-      this.consumers(0).poll(50)
-      this.consumers(0).assignment == shrunkenSubscriptions.asJava
-    }, s"Expected partitions ${shrunkenSubscriptions.asJava} but actually got ${this.consumers(0).assignment}")
+      this.consumers.head.poll(50)
+      this.consumers.head.assignment == shrunkenSubscriptions.asJava
+    }, s"Expected partitions ${shrunkenSubscriptions.asJava} but actually got ${this.consumers.head.assignment}")
   }
 
   @Test
   def testPartitionsFor() {
     val numParts = 2
     TestUtils.createTopic(this.zkUtils, "part-test", numParts, 1, this.servers)
-    val parts = this.consumers(0).partitionsFor("part-test")
+    val parts = this.consumers.head.partitionsFor("part-test")
     assertNotNull(parts)
     assertEquals(2, parts.size)
   }
 
   @Test
   def testPartitionsForAutoCreate() {
-    val partitions = this.consumers(0).partitionsFor("non-exist-topic")
+    val partitions = this.consumers.head.partitionsFor("non-exist-topic")
     assertFalse(partitions.isEmpty)
   }
 
   @Test(expected = classOf[InvalidTopicException])
   def testPartitionsForInvalidTopic() {
-    this.consumers(0).partitionsFor(";3# ads,{234")
+    this.consumers.head.partitionsFor(";3# ads,{234")
   }
 
   @Test
   def testSeek() {
-    val consumer = this.consumers(0)
+    val consumer = this.consumers.head
     val totalRecords = 50L
     val mid = totalRecords / 2
 
@@ -366,23 +366,23 @@ class PlaintextConsumerTest extends BaseConsumerTest {
   def testPositionAndCommit() {
     sendRecords(5)
 
-    assertNull(this.consumers(0).committed(new TopicPartition(topic, 15)))
+    assertNull(this.consumers.head.committed(new TopicPartition(topic, 15)))
 
     // position() on a partition that we aren't subscribed to throws an exception
     intercept[IllegalArgumentException] {
-      this.consumers(0).position(new TopicPartition(topic, 15))
+      this.consumers.head.position(new TopicPartition(topic, 15))
     }
 
-    this.consumers(0).assign(List(tp).asJava)
+    this.consumers.head.assign(List(tp).asJava)
 
-    assertEquals("position() on a partition that we are subscribed to should reset the offset", 0L, this.consumers(0).position(tp))
-    this.consumers(0).commitSync()
-    assertEquals(0L, this.consumers(0).committed(tp).offset)
+    assertEquals("position() on a partition that we are subscribed to should reset the offset", 0L, this.consumers.head.position(tp))
+    this.consumers.head.commitSync()
+    assertEquals(0L, this.consumers.head.committed(tp).offset)
 
-    consumeAndVerifyRecords(consumer = this.consumers(0), numRecords = 5, startingOffset = 0)
-    assertEquals("After consuming 5 records, position should be 5", 5L, this.consumers(0).position(tp))
-    this.consumers(0).commitSync()
-    assertEquals("Committed offset should be returned", 5L, this.consumers(0).committed(tp).offset)
+    consumeAndVerifyRecords(consumer = this.consumers.head, numRecords = 5, startingOffset = 0)
+    assertEquals("After consuming 5 records, position should be 5", 5L, this.consumers.head.position(tp))
+    this.consumers.head.commitSync()
+    assertEquals("Committed offset should be returned", 5L, this.consumers.head.committed(tp).offset)
 
     sendRecords(1)
 
@@ -395,18 +395,18 @@ class PlaintextConsumerTest extends BaseConsumerTest {
   def testPartitionPauseAndResume() {
     val partitions = List(tp).asJava
     sendRecords(5)
-    this.consumers(0).assign(partitions)
-    consumeAndVerifyRecords(consumer = this.consumers(0), numRecords = 5, startingOffset = 0)
-    this.consumers(0).pause(partitions)
+    this.consumers.head.assign(partitions)
+    consumeAndVerifyRecords(consumer = this.consumers.head, numRecords = 5, startingOffset = 0)
+    this.consumers.head.pause(partitions)
     sendRecords(5)
-    assertTrue(this.consumers(0).poll(0).isEmpty)
-    this.consumers(0).resume(partitions)
-    consumeAndVerifyRecords(consumer = this.consumers(0), numRecords = 5, startingOffset = 5)
+    assertTrue(this.consumers.head.poll(0).isEmpty)
+    this.consumers.head.resume(partitions)
+    consumeAndVerifyRecords(consumer = this.consumers.head, numRecords = 5, startingOffset = 5)
   }
 
   @Test
   def testFetchInvalidOffset() {
-    this.consumerConfig.setProperty(ConsumerConfig.AUTO_OFFSET_RESET_CONFIG, "none");
+    this.consumerConfig.setProperty(ConsumerConfig.AUTO_OFFSET_RESET_CONFIG, "none")
     val consumer0 = new KafkaConsumer(this.consumerConfig, new ByteArrayDeserializer(), new ByteArrayDeserializer())
     consumers += consumer0
 
@@ -441,7 +441,7 @@ class PlaintextConsumerTest extends BaseConsumerTest {
 
     // produce a record that is larger than the configured fetch size
     val record = new ProducerRecord[Array[Byte], Array[Byte]](tp.topic(), tp.partition(), "key".getBytes, new Array[Byte](maxFetchBytes + 1))
-    this.producers(0).send(record)
+    this.producers.head.send(record)
 
     // consuming a too-large record should fail
     consumer0.assign(List(tp).asJava)
@@ -713,14 +713,14 @@ class PlaintextConsumerTest extends BaseConsumerTest {
     val numRecords = 50
     // Test non-compressed messages
     sendRecords(numRecords, tp)
-    this.consumers(0).assign(List(tp).asJava)
-    consumeAndVerifyRecords(consumer = this.consumers(0), numRecords = numRecords, startingOffset = 0, startingKeyAndValueIndex = 0,
+    this.consumers.head.assign(List(tp).asJava)
+    consumeAndVerifyRecords(consumer = this.consumers.head, numRecords = numRecords, startingOffset = 0, startingKeyAndValueIndex = 0,
       startingTimestamp = 0)
 
     // Test compressed messages
     sendCompressedMessages(numRecords, tp2)
-    this.consumers(0).assign(List(tp2).asJava)
-    consumeAndVerifyRecords(consumer = this.consumers(0), numRecords = numRecords, tp = tp2, startingOffset = 0, startingKeyAndValueIndex = 0,
+    this.consumers.head.assign(List(tp2).asJava)
+    consumeAndVerifyRecords(consumer = this.consumers.head, numRecords = numRecords, tp = tp2, startingOffset = 0, startingKeyAndValueIndex = 0,
       startingTimestamp = 0)
   }
 
@@ -737,15 +737,15 @@ class PlaintextConsumerTest extends BaseConsumerTest {
     // Test non-compressed messages
     val tp1 = new TopicPartition(topicName, 0)
     sendRecords(numRecords, tp1)
-    this.consumers(0).assign(List(tp1).asJava)
-    consumeAndVerifyRecords(consumer = this.consumers(0), numRecords = numRecords, tp = tp1, startingOffset = 0, startingKeyAndValueIndex = 0,
+    this.consumers.head.assign(List(tp1).asJava)
+    consumeAndVerifyRecords(consumer = this.consumers.head, numRecords = numRecords, tp = tp1, startingOffset = 0, startingKeyAndValueIndex = 0,
       startingTimestamp = startTime, timestampType = TimestampType.LOG_APPEND_TIME)
 
     // Test compressed messages
     val tp2 = new TopicPartition(topicName, 1)
     sendCompressedMessages(numRecords, tp2)
-    this.consumers(0).assign(List(tp2).asJava)
-    consumeAndVerifyRecords(consumer = this.consumers(0), numRecords = numRecords, tp = tp2, startingOffset = 0, startingKeyAndValueIndex = 0,
+    this.consumers.head.assign(List(tp2).asJava)
+    consumeAndVerifyRecords(consumer = this.consumers.head, numRecords = numRecords, tp = tp2, startingOffset = 0, startingKeyAndValueIndex = 0,
       startingTimestamp = startTime, timestampType = TimestampType.LOG_APPEND_TIME)
   }
 
diff --git a/core/src/test/scala/integration/kafka/api/SaslMultiMechanismConsumerTest.scala b/core/src/test/scala/integration/kafka/api/SaslMultiMechanismConsumerTest.scala
index fc79c60edfb2d..5814e9463560c 100644
--- a/core/src/test/scala/integration/kafka/api/SaslMultiMechanismConsumerTest.scala
+++ b/core/src/test/scala/integration/kafka/api/SaslMultiMechanismConsumerTest.scala
@@ -32,8 +32,8 @@ class SaslMultiMechanismConsumerTest extends BaseConsumerTest with SaslTestHarne
   @Test
   def testMultipleBrokerMechanisms() {
 
-    val plainSaslProducer = producers(0)
-    val plainSaslConsumer = consumers(0)
+    val plainSaslProducer = producers.head
+    val plainSaslConsumer = consumers.head
 
     val gssapiSaslProperties = kafkaSaslProperties("GSSAPI")
     val gssapiSaslProducer = TestUtils.createNewProducer(brokerList,
diff --git a/core/src/test/scala/kafka/tools/TestLogCleaning.scala b/core/src/test/scala/kafka/tools/TestLogCleaning.scala
index 2e288ecd3c033..65561009ad140 100755
--- a/core/src/test/scala/kafka/tools/TestLogCleaning.scala
+++ b/core/src/test/scala/kafka/tools/TestLogCleaning.scala
@@ -311,9 +311,9 @@ object TestLogCleaning {
   
 }
 
-case class TestRecord(val topic: String, val key: Int, val value: Long, val delete: Boolean) {
+case class TestRecord(topic: String, key: Int, value: Long, delete: Boolean) {
   def this(pieces: Array[String]) = this(pieces(0), pieces(1).toInt, pieces(2).toLong, pieces(3) == "d")
   def this(line: String) = this(line.split("\t"))
-  override def toString() = topic + "\t" +  key + "\t" + value + "\t" + (if(delete) "d" else "u")
+  override def toString = topic + "\t" +  key + "\t" + value + "\t" + (if(delete) "d" else "u")
   def topicAndKey = topic + key
 }
diff --git a/core/src/test/scala/other/kafka/TestOffsetManager.scala b/core/src/test/scala/other/kafka/TestOffsetManager.scala
index 5c2f1ae76c2d0..944519198945c 100644
--- a/core/src/test/scala/other/kafka/TestOffsetManager.scala
+++ b/core/src/test/scala/other/kafka/TestOffsetManager.scala
@@ -255,7 +255,7 @@ object TestOffsetManager {
     var statsThread: StatsThread = null
     try {
       zkUtils = ZkUtils(zookeeper, 6000, 2000, false)
-      commitThreads = (0 to (threadCount-1)).map { threadId =>
+      commitThreads = (0 until threadCount).map { threadId =>
         new CommitThread(threadId, partitionCount, commitIntervalMs, zkUtils)
       }
 
diff --git a/core/src/test/scala/unit/kafka/admin/AddPartitionsTest.scala b/core/src/test/scala/unit/kafka/admin/AddPartitionsTest.scala
index ab8d36314477f..763e4ec8af8a1 100755
--- a/core/src/test/scala/unit/kafka/admin/AddPartitionsTest.scala
+++ b/core/src/test/scala/unit/kafka/admin/AddPartitionsTest.scala
@@ -134,7 +134,7 @@ class AddPartitionsTest extends ZooKeeperTestHarness {
     assertEquals(partitionDataForTopic2(2).partitionId, 2)
     val replicas = partitionDataForTopic2(1).replicas
     assertEquals(replicas.size, 2)
-    assert(replicas(0).id == 0 || replicas(0).id == 1)
+    assert(replicas.head.id == 0 || replicas.head.id == 1)
     assert(replicas(1).id == 0 || replicas(1).id == 1)
   }
 
diff --git a/core/src/test/scala/unit/kafka/admin/AdminTest.scala b/core/src/test/scala/unit/kafka/admin/AdminTest.scala
index 21bb6ab4631b3..7df141143fded 100755
--- a/core/src/test/scala/unit/kafka/admin/AdminTest.scala
+++ b/core/src/test/scala/unit/kafka/admin/AdminTest.scala
@@ -127,7 +127,7 @@ class AdminTest extends ZooKeeperTestHarness with Logging with RackAwareTest {
     AdminUtils.createOrUpdateTopicPartitionAssignmentPathInZK(zkUtils, topic, expectedReplicaAssignment)
     // create leaders for all partitions
     TestUtils.makeLeaderForPartition(zkUtils, topic, leaderForPartitionMap, 1)
-    val actualReplicaList = leaderForPartitionMap.keys.toArray.map(p => (p -> zkUtils.getReplicasForPartition(topic, p))).toMap
+    val actualReplicaList = leaderForPartitionMap.keys.toArray.map(p => p -> zkUtils.getReplicasForPartition(topic, p)).toMap
     assertEquals(expectedReplicaAssignment.size, actualReplicaList.size)
     for(i <- 0 until actualReplicaList.size)
       assertEquals(expectedReplicaAssignment.get(i).get, actualReplicaList(i))
@@ -174,9 +174,9 @@ class AdminTest extends ZooKeeperTestHarness with Logging with RackAwareTest {
     assertTrue("Partition reassignment attempt failed for [test, 0]", reassignPartitionsCommand.reassignPartitions())
     // wait until reassignment is completed
     TestUtils.waitUntilTrue(() => {
-        val partitionsBeingReassigned = zkUtils.getPartitionsBeingReassigned().mapValues(_.newReplicas);
+        val partitionsBeingReassigned = zkUtils.getPartitionsBeingReassigned().mapValues(_.newReplicas)
         ReassignPartitionsCommand.checkIfPartitionReassignmentSucceeded(zkUtils, topicAndPartition, newReplicas,
-        Map(topicAndPartition -> newReplicas), partitionsBeingReassigned) == ReassignmentCompleted;
+        Map(topicAndPartition -> newReplicas), partitionsBeingReassigned) == ReassignmentCompleted
       },
       "Partition reassignment should complete")
     val assignedReplicas = zkUtils.getReplicasForPartition(topic, partitionToBeReassigned)
@@ -205,9 +205,9 @@ class AdminTest extends ZooKeeperTestHarness with Logging with RackAwareTest {
     assertTrue("Partition reassignment failed for test, 0", reassignPartitionsCommand.reassignPartitions())
     // wait until reassignment is completed
     TestUtils.waitUntilTrue(() => {
-        val partitionsBeingReassigned = zkUtils.getPartitionsBeingReassigned().mapValues(_.newReplicas);
+        val partitionsBeingReassigned = zkUtils.getPartitionsBeingReassigned().mapValues(_.newReplicas)
         ReassignPartitionsCommand.checkIfPartitionReassignmentSucceeded(zkUtils, topicAndPartition, newReplicas,
-          Map(topicAndPartition -> newReplicas), partitionsBeingReassigned) == ReassignmentCompleted;
+          Map(topicAndPartition -> newReplicas), partitionsBeingReassigned) == ReassignmentCompleted
       },
       "Partition reassignment should complete")
     val assignedReplicas = zkUtils.getReplicasForPartition(topic, partitionToBeReassigned)
@@ -236,9 +236,9 @@ class AdminTest extends ZooKeeperTestHarness with Logging with RackAwareTest {
     assertTrue("Partition reassignment failed for test, 0", reassignPartitionsCommand.reassignPartitions())
     // wait until reassignment is completed
     TestUtils.waitUntilTrue(() => {
-        val partitionsBeingReassigned = zkUtils.getPartitionsBeingReassigned().mapValues(_.newReplicas);
+        val partitionsBeingReassigned = zkUtils.getPartitionsBeingReassigned().mapValues(_.newReplicas)
         ReassignPartitionsCommand.checkIfPartitionReassignmentSucceeded(zkUtils, topicAndPartition, newReplicas,
-          Map(topicAndPartition -> newReplicas), partitionsBeingReassigned) == ReassignmentCompleted;
+          Map(topicAndPartition -> newReplicas), partitionsBeingReassigned) == ReassignmentCompleted
       },
       "Partition reassignment should complete")
     val assignedReplicas = zkUtils.getReplicasForPartition(topic, partitionToBeReassigned)
diff --git a/core/src/test/scala/unit/kafka/admin/ConfigCommandTest.scala b/core/src/test/scala/unit/kafka/admin/ConfigCommandTest.scala
index bcfcfad113314..7c71aededfc3e 100644
--- a/core/src/test/scala/unit/kafka/admin/ConfigCommandTest.scala
+++ b/core/src/test/scala/unit/kafka/admin/ConfigCommandTest.scala
@@ -63,6 +63,6 @@ class ConfigCommandTest extends ZooKeeperTestHarness with Logging {
 
     val deletedProps = ConfigCommand.parseConfigsToBeDeleted(createOpts)
     assertEquals(1, deletedProps.size)
-    assertEquals("a", deletedProps(0))
+    assertEquals("a", deletedProps.head)
   }
 }
diff --git a/core/src/test/scala/unit/kafka/admin/DeleteTopicTest.scala b/core/src/test/scala/unit/kafka/admin/DeleteTopicTest.scala
index 477dcc836dfa6..1e1a98c21c6e1 100644
--- a/core/src/test/scala/unit/kafka/admin/DeleteTopicTest.scala
+++ b/core/src/test/scala/unit/kafka/admin/DeleteTopicTest.scala
@@ -121,9 +121,9 @@ class DeleteTopicTest extends ZooKeeperTestHarness {
     assertTrue("Partition reassignment should fail for [test,0]", reassignPartitionsCommand.reassignPartitions())
     // wait until reassignment is completed
     TestUtils.waitUntilTrue(() => {
-      val partitionsBeingReassigned = zkUtils.getPartitionsBeingReassigned().mapValues(_.newReplicas);
+      val partitionsBeingReassigned = zkUtils.getPartitionsBeingReassigned().mapValues(_.newReplicas)
       ReassignPartitionsCommand.checkIfPartitionReassignmentSucceeded(zkUtils, topicAndPartition, newReplicas,
-        Map(topicAndPartition -> newReplicas), partitionsBeingReassigned) == ReassignmentFailed;
+        Map(topicAndPartition -> newReplicas), partitionsBeingReassigned) == ReassignmentFailed
     }, "Partition reassignment shouldn't complete.")
     val controllerId = zkUtils.getController()
     val controller = servers.filter(s => s.config.brokerId == controllerId).head
@@ -223,17 +223,17 @@ class DeleteTopicTest extends ZooKeeperTestHarness {
     val topic = topicAndPartition.topic
 
     val brokerConfigs = TestUtils.createBrokerConfigs(3, zkConnect, false)
-    brokerConfigs(0).setProperty("delete.topic.enable", "true")
-    brokerConfigs(0).setProperty("log.cleaner.enable","true")
-    brokerConfigs(0).setProperty("log.cleanup.policy","compact")
-    brokerConfigs(0).setProperty("log.segment.bytes","100")
-    brokerConfigs(0).setProperty("log.segment.delete.delay.ms","1000")
-    brokerConfigs(0).setProperty("log.cleaner.dedupe.buffer.size","1048577")
+    brokerConfigs.head.setProperty("delete.topic.enable", "true")
+    brokerConfigs.head.setProperty("log.cleaner.enable","true")
+    brokerConfigs.head.setProperty("log.cleanup.policy","compact")
+    brokerConfigs.head.setProperty("log.segment.bytes","100")
+    brokerConfigs.head.setProperty("log.segment.delete.delay.ms","1000")
+    brokerConfigs.head.setProperty("log.cleaner.dedupe.buffer.size","1048577")
 
     val servers = createTestTopicAndCluster(topic,brokerConfigs)
 
     // for simplicity, we are validating cleaner offsets on a single broker
-    val server = servers(0)
+    val server = servers.head
     val log = server.logManager.getLog(topicAndPartition).get
 
     // write to the topic to activate cleaner
diff --git a/core/src/test/scala/unit/kafka/consumer/ConsumerIteratorTest.scala b/core/src/test/scala/unit/kafka/consumer/ConsumerIteratorTest.scala
index ac7ce51417814..653b40cc5c523 100755
--- a/core/src/test/scala/unit/kafka/consumer/ConsumerIteratorTest.scala
+++ b/core/src/test/scala/unit/kafka/consumer/ConsumerIteratorTest.scala
@@ -68,7 +68,7 @@ class ConsumerIteratorTest extends KafkaServerTestHarness {
     val messages = messageStrings.map(s => new Message(s.getBytes))
     val messageSet = new ByteBufferMessageSet(DefaultCompressionCodec, new LongRef(0), messages:_*)
 
-    topicInfos(0).enqueue(messageSet)
+    topicInfos.head.enqueue(messageSet)
     assertEquals(1, queue.size)
     queue.put(ZookeeperConsumerConnector.shutdownCommand)
 
@@ -92,7 +92,7 @@ class ConsumerIteratorTest extends KafkaServerTestHarness {
     val messages = messageStrings.map(s => new Message(s.getBytes))
     val messageSet = new ByteBufferMessageSet(NoCompressionCodec, new LongRef(0), messages:_*)
 
-    topicInfos(0).enqueue(messageSet)
+    topicInfos.head.enqueue(messageSet)
     assertEquals(1, queue.size)
 
     val iter = new ConsumerIterator[String, String](queue,
diff --git a/core/src/test/scala/unit/kafka/consumer/ZookeeperConsumerConnectorTest.scala b/core/src/test/scala/unit/kafka/consumer/ZookeeperConsumerConnectorTest.scala
index a69fba17a73f4..b05479438e6cf 100644
--- a/core/src/test/scala/unit/kafka/consumer/ZookeeperConsumerConnectorTest.scala
+++ b/core/src/test/scala/unit/kafka/consumer/ZookeeperConsumerConnectorTest.scala
@@ -430,7 +430,7 @@ class ZookeeperConsumerConnectorTest extends KafkaServerTestHarness with Logging
   private class TestConsumerRebalanceListener extends ConsumerRebalanceListener {
     var beforeReleasingPartitionsCalled: Boolean = false
     var beforeStartingFetchersCalled: Boolean = false
-    var consumerId: String = "";
+    var consumerId: String = ""
     var partitionOwnership: java.util.Map[String, java.util.Set[java.lang.Integer]] = null
     var globalPartitionOwnership: java.util.Map[String, java.util.Map[java.lang.Integer, ConsumerThreadId]] = null
 
diff --git a/core/src/test/scala/unit/kafka/controller/ControllerFailoverTest.scala b/core/src/test/scala/unit/kafka/controller/ControllerFailoverTest.scala
index 91ac1f62a6c95..699715ba4351b 100644
--- a/core/src/test/scala/unit/kafka/controller/ControllerFailoverTest.scala
+++ b/core/src/test/scala/unit/kafka/controller/ControllerFailoverTest.scala
@@ -65,7 +65,7 @@ class ControllerFailoverTest extends KafkaServerTestHarness with Logging {
   @Test
   def testMetadataUpdate() {
     log.setLevel(Level.INFO)
-    var controller: KafkaServer = this.servers.head;
+    var controller: KafkaServer = this.servers.head
     // Find the current controller
     val epochMap: mutable.Map[Int, Int] = mutable.Map.empty
     for (server <- this.servers) {
@@ -121,7 +121,7 @@ class ControllerFailoverTest extends KafkaServerTestHarness with Logging {
     var counter = 0
     while (!found && counter < 10) {
       for (server <- this.servers) {
-        val previousEpoch = (epochMap get server.config.brokerId) match {
+        val previousEpoch = epochMap get server.config.brokerId match {
           case Some(epoch) =>
             epoch
           case None =>
@@ -130,7 +130,7 @@ class ControllerFailoverTest extends KafkaServerTestHarness with Logging {
         }
 
         if (server.kafkaController.isActive
-            && (previousEpoch) < server.kafkaController.epoch) {
+            && previousEpoch < server.kafkaController.epoch) {
           controller = server
           found = true
         }
diff --git a/core/src/test/scala/unit/kafka/coordinator/GroupCoordinatorResponseTest.scala b/core/src/test/scala/unit/kafka/coordinator/GroupCoordinatorResponseTest.scala
index beab1b542e173..dc343fa1d0207 100644
--- a/core/src/test/scala/unit/kafka/coordinator/GroupCoordinatorResponseTest.scala
+++ b/core/src/test/scala/unit/kafka/coordinator/GroupCoordinatorResponseTest.scala
@@ -802,7 +802,7 @@ class GroupCoordinatorResponseTest extends JUnitSuite {
     val (error, groups) = groupCoordinator.handleListGroups()
     assertEquals(Errors.NONE, error)
     assertEquals(1, groups.size)
-    assertEquals(GroupOverview("groupId", "consumer"), groups(0))
+    assertEquals(GroupOverview("groupId", "consumer"), groups.head)
   }
 
   @Test
@@ -814,7 +814,7 @@ class GroupCoordinatorResponseTest extends JUnitSuite {
     val (error, groups) = groupCoordinator.handleListGroups()
     assertEquals(Errors.NONE, error)
     assertEquals(1, groups.size)
-    assertEquals(GroupOverview("groupId", "consumer"), groups(0))
+    assertEquals(GroupOverview("groupId", "consumer"), groups.head)
   }
 
   @Test
diff --git a/core/src/test/scala/unit/kafka/integration/PrimitiveApiTest.scala b/core/src/test/scala/unit/kafka/integration/PrimitiveApiTest.scala
index 85e9cad3d248f..140f615225792 100755
--- a/core/src/test/scala/unit/kafka/integration/PrimitiveApiTest.scala
+++ b/core/src/test/scala/unit/kafka/integration/PrimitiveApiTest.scala
@@ -62,7 +62,7 @@ class PrimitiveApiTest extends ProducerConsumerTestHarness {
     val partitionRequests = immutable.Map[TopicAndPartition, PartitionFetchInfo]()
     val request = new FetchRequest(requestInfo = partitionRequests)
     val fetched = consumer.fetch(request)
-    assertTrue(!fetched.hasError && fetched.data.size == 0)
+    assertTrue(!fetched.hasError && fetched.data.isEmpty)
   }
 
   @Test
@@ -152,7 +152,7 @@ class PrimitiveApiTest extends ProducerConsumerTestHarness {
         response.data.values.foreach(pdata => ErrorMapping.maybeThrowException(pdata.error))
         fail("Expected exception when fetching message with invalid offset")
       } catch {
-        case e: OffsetOutOfRangeException => "this is good"
+        case e: OffsetOutOfRangeException => // This is good.
       }
     }
 
@@ -168,7 +168,7 @@ class PrimitiveApiTest extends ProducerConsumerTestHarness {
         response.data.values.foreach(pdata => ErrorMapping.maybeThrowException(pdata.error))
         fail("Expected exception when fetching message with invalid partition")
       } catch {
-        case e: UnknownTopicOrPartitionException => "this is good"
+        case e: UnknownTopicOrPartitionException => // This is good.
       }
     }
 
diff --git a/core/src/test/scala/unit/kafka/integration/ProducerConsumerTestHarness.scala b/core/src/test/scala/unit/kafka/integration/ProducerConsumerTestHarness.scala
index 2fdfc48b2fdb0..bdf116f9f75d4 100644
--- a/core/src/test/scala/unit/kafka/integration/ProducerConsumerTestHarness.scala
+++ b/core/src/test/scala/unit/kafka/integration/ProducerConsumerTestHarness.scala
@@ -36,7 +36,7 @@ trait ProducerConsumerTestHarness extends KafkaServerTestHarness {
       encoder = classOf[StringEncoder].getName,
       keyEncoder = classOf[StringEncoder].getName,
       partitioner = classOf[StaticPartitioner].getName)
-    consumer = new SimpleConsumer(host, servers(0).boundPort(), 1000000, 64 * 1024, "")
+    consumer = new SimpleConsumer(host, servers.head.boundPort(), 1000000, 64 * 1024, "")
   }
 
   @After
diff --git a/core/src/test/scala/unit/kafka/log/CleanerTest.scala b/core/src/test/scala/unit/kafka/log/CleanerTest.scala
index 752a260fb28a8..82121218928a8 100755
--- a/core/src/test/scala/unit/kafka/log/CleanerTest.scala
+++ b/core/src/test/scala/unit/kafka/log/CleanerTest.scala
@@ -67,7 +67,7 @@ class CleanerTest extends JUnitSuite {
     while(log.numberOfSegments < 4)
       log.append(message(log.logEndOffset.toInt, log.logEndOffset.toInt))
     val keysFound = keysInLog(log)
-    assertEquals((0L until log.logEndOffset), keysFound)
+    assertEquals(0L until log.logEndOffset, keysFound)
     
     // pretend we have the following keys
     val keys = immutable.ListSet(1, 3, 5, 7, 9)
@@ -211,7 +211,7 @@ class CleanerTest extends JUnitSuite {
     // grouping by very large values should result in a single group with all the segments in it
     var groups = cleaner.groupSegmentsBySize(log.logSegments, maxSize = Int.MaxValue, maxIndexSize = Int.MaxValue)
     assertEquals(1, groups.size)
-    assertEquals(log.numberOfSegments, groups(0).size)
+    assertEquals(log.numberOfSegments, groups.head.size)
     checkSegmentOrder(groups)
     
     // grouping by very small values should result in all groups having one entry
diff --git a/core/src/test/scala/unit/kafka/log/FileMessageSetTest.scala b/core/src/test/scala/unit/kafka/log/FileMessageSetTest.scala
index 534443ce3203e..417aa7528e28c 100644
--- a/core/src/test/scala/unit/kafka/log/FileMessageSetTest.scala
+++ b/core/src/test/scala/unit/kafka/log/FileMessageSetTest.scala
@@ -145,7 +145,7 @@ class FileMessageSetTest extends BaseMessageSetTestCases {
    */
   @Test
   def testTruncate() {
-    val message = messageSet.toList(0)
+    val message = messageSet.toList.head
     val end = messageSet.searchFor(1, 0).position
     messageSet.truncateTo(end)
     assertEquals(List(message), messageSet.toList)
diff --git a/core/src/test/scala/unit/kafka/log/LogCleanerIntegrationTest.scala b/core/src/test/scala/unit/kafka/log/LogCleanerIntegrationTest.scala
index cc9873c862a60..a862cb181ae72 100755
--- a/core/src/test/scala/unit/kafka/log/LogCleanerIntegrationTest.scala
+++ b/core/src/test/scala/unit/kafka/log/LogCleanerIntegrationTest.scala
@@ -75,7 +75,7 @@ class LogCleanerIntegrationTest(compressionCodec: String) {
     cleaner.awaitCleaned("log", 0, firstDirty2)
 
     val lastCleaned2 = cleaner.cleanerManager.allCleanerCheckpoints.get(TopicAndPartition("log", 0)).get
-    assertTrue(s"log cleaner should have processed up to offset $firstDirty2", lastCleaned2 >= firstDirty2);
+    assertTrue(s"log cleaner should have processed up to offset $firstDirty2", lastCleaned2 >= firstDirty2)
 
     val read2 = readFromLog(log)
     assertEquals("Contents of the map shouldn't change.", appends2.toMap, read2.toMap)
diff --git a/core/src/test/scala/unit/kafka/log/LogManagerTest.scala b/core/src/test/scala/unit/kafka/log/LogManagerTest.scala
index f290d54702f96..7b52a094c6c20 100755
--- a/core/src/test/scala/unit/kafka/log/LogManagerTest.scala
+++ b/core/src/test/scala/unit/kafka/log/LogManagerTest.scala
@@ -107,7 +107,7 @@ class LogManagerTest {
       log.read(0, 1024)
       fail("Should get exception from fetching earlier.")
     } catch {
-      case e: OffsetOutOfRangeException => "This is good."
+      case e: OffsetOutOfRangeException => // This is good.
     }
     // log should still be appendable
     log.append(TestUtils.singleMessageSet("test".getBytes()))
@@ -152,7 +152,7 @@ class LogManagerTest {
       log.read(0, 1024)
       fail("Should get exception from fetching earlier.")
     } catch {
-      case e: OffsetOutOfRangeException => "This is good."
+      case e: OffsetOutOfRangeException => // This is good.
     }
     // log should still be appendable
     log.append(TestUtils.singleMessageSet("test".getBytes()))
diff --git a/core/src/test/scala/unit/kafka/log/LogTest.scala b/core/src/test/scala/unit/kafka/log/LogTest.scala
index f48f6b1e85fa5..33dd68ef3ab42 100755
--- a/core/src/test/scala/unit/kafka/log/LogTest.scala
+++ b/core/src/test/scala/unit/kafka/log/LogTest.scala
@@ -617,10 +617,10 @@ class LogTest extends JUnitSuite {
     for (i<- 1 to msgPerSeg)
       log.append(set)
     assertEquals("There should be exactly 2 segment.", 2, log.numberOfSegments)
-    assertEquals("The index of the first segment should be trimmed to empty", 0, log.logSegments.toList(0).index.maxEntries)
+    assertEquals("The index of the first segment should be trimmed to empty", 0, log.logSegments.toList.head.index.maxEntries)
     log.truncateTo(0)
     assertEquals("There should be exactly 1 segment.", 1, log.numberOfSegments)
-    assertEquals("The index of segment 1 should be resized to maxIndexSize", log.config.maxIndexSize/8, log.logSegments.toList(0).index.maxEntries)
+    assertEquals("The index of segment 1 should be resized to maxIndexSize", log.config.maxIndexSize/8, log.logSegments.toList.head.index.maxEntries)
     for (i<- 1 to msgPerSeg)
       log.append(set)
     assertEquals("There should be exactly 1 segment.", 1, log.numberOfSegments)
diff --git a/core/src/test/scala/unit/kafka/message/ByteBufferMessageSetTest.scala b/core/src/test/scala/unit/kafka/message/ByteBufferMessageSetTest.scala
index 758dad22eab95..8f66d62acf76f 100644
--- a/core/src/test/scala/unit/kafka/message/ByteBufferMessageSetTest.scala
+++ b/core/src/test/scala/unit/kafka/message/ByteBufferMessageSetTest.scala
@@ -383,7 +383,7 @@ class ByteBufferMessageSetTest extends BaseMessageSetTestCases {
   
   /* check that offsets are assigned based on byte offset from the given base offset */
   def checkOffsets(messages: ByteBufferMessageSet, baseOffset: Long) {
-    assertTrue("Message set should not be empty", messages.size > 0)
+    assertTrue("Message set should not be empty", messages.nonEmpty)
     var offset = baseOffset
     for(entry <- messages) {
       assertEquals("Unexpected offset in message set iterator", offset, entry.offset)
diff --git a/core/src/test/scala/unit/kafka/message/MessageTest.scala b/core/src/test/scala/unit/kafka/message/MessageTest.scala
index 3c8a41fca7886..5c021257dda7b 100755
--- a/core/src/test/scala/unit/kafka/message/MessageTest.scala
+++ b/core/src/test/scala/unit/kafka/message/MessageTest.scala
@@ -28,12 +28,12 @@ import org.junit.{Before, Test}
 import kafka.utils.TestUtils
 import org.apache.kafka.common.utils.Utils
 
-case class MessageTestVal(val key: Array[Byte], 
-                          val payload: Array[Byte],
-                          val codec: CompressionCodec,
-                          val timestamp: Long,
-                          val magicValue: Byte,
-                          val message: Message)
+case class MessageTestVal(key: Array[Byte],
+                          payload: Array[Byte],
+                          codec: CompressionCodec,
+                          timestamp: Long,
+                          magicValue: Byte,
+                          message: Message)
 
 class MessageTest extends JUnitSuite {
 
diff --git a/core/src/test/scala/unit/kafka/network/SocketServerTest.scala b/core/src/test/scala/unit/kafka/network/SocketServerTest.scala
index d2154306b94e0..e60f350e2b0cd 100644
--- a/core/src/test/scala/unit/kafka/network/SocketServerTest.scala
+++ b/core/src/test/scala/unit/kafka/network/SocketServerTest.scala
@@ -15,7 +15,7 @@
  * limitations under the License.
  */
 
-package kafka.network;
+package kafka.network
 
 import java.net._
 import javax.net.ssl._
diff --git a/core/src/test/scala/unit/kafka/producer/ProducerTest.scala b/core/src/test/scala/unit/kafka/producer/ProducerTest.scala
index cf25cdbf1c635..dc73db3f1c4ef 100755
--- a/core/src/test/scala/unit/kafka/producer/ProducerTest.scala
+++ b/core/src/test/scala/unit/kafka/producer/ProducerTest.scala
@@ -186,11 +186,11 @@ class ProducerTest extends ZooKeeperTestHarness with Logging{
     }
     assertEquals("Should have fetched 2 messages", 2, messageSet.size)
     // Message 1
-    assertTrue(ByteBuffer.wrap("test1".getBytes).equals(messageSet(0).message.payload))
-    assertTrue(ByteBuffer.wrap("test".getBytes).equals(messageSet(0).message.key))
-    assertTrue(messageSet(0).message.timestamp >= startTime && messageSet(0).message.timestamp < endTime)
-    assertEquals(TimestampType.CREATE_TIME, messageSet(0).message.timestampType)
-    assertEquals(Message.MagicValue_V1, messageSet(0).message.magic)
+    assertTrue(ByteBuffer.wrap("test1".getBytes).equals(messageSet.head.message.payload))
+    assertTrue(ByteBuffer.wrap("test".getBytes).equals(messageSet.head.message.key))
+    assertTrue(messageSet.head.message.timestamp >= startTime && messageSet.head.message.timestamp < endTime)
+    assertEquals(TimestampType.CREATE_TIME, messageSet.head.message.timestampType)
+    assertEquals(Message.MagicValue_V1, messageSet.head.message.magic)
 
     // Message 2
     assertTrue(ByteBuffer.wrap("test2".getBytes).equals(messageSet(1).message.payload))
diff --git a/core/src/test/scala/unit/kafka/producer/SyncProducerTest.scala b/core/src/test/scala/unit/kafka/producer/SyncProducerTest.scala
index 8e234d264bb3a..270a794fad446 100644
--- a/core/src/test/scala/unit/kafka/producer/SyncProducerTest.scala
+++ b/core/src/test/scala/unit/kafka/producer/SyncProducerTest.scala
@@ -99,7 +99,7 @@ class SyncProducerTest extends KafkaServerTestHarness {
     val producer = new SyncProducer(new SyncProducerConfig(props))
     val response = producer.send(emptyRequest)
     assertTrue(response != null)
-    assertTrue(!response.hasError && response.status.size == 0)
+    assertTrue(!response.hasError && response.status.isEmpty)
   }
 
   @Test
@@ -110,7 +110,7 @@ class SyncProducerTest extends KafkaServerTestHarness {
     val producer = new SyncProducer(new SyncProducerConfig(props))
     TestUtils.createTopic(zkUtils, "test", numPartitions = 1, replicationFactor = 1, servers = servers)
 
-    val message1 = new Message(new Array[Byte](configs(0).messageMaxBytes + 1))
+    val message1 = new Message(new Array[Byte](configs.head.messageMaxBytes + 1))
     val messageSet1 = new ByteBufferMessageSet(compressionCodec = NoCompressionCodec, messages = message1)
     val response1 = producer.send(produceRequest("test", 0, messageSet1, acks = 1))
 
@@ -118,7 +118,7 @@ class SyncProducerTest extends KafkaServerTestHarness {
     assertEquals(Errors.MESSAGE_TOO_LARGE.code, response1.status(TopicAndPartition("test", 0)).error)
     assertEquals(-1L, response1.status(TopicAndPartition("test", 0)).offset)
 
-    val safeSize = configs(0).messageMaxBytes - Message.MinMessageOverhead - Message.TimestampLength - MessageSet.LogOverhead - 1
+    val safeSize = configs.head.messageMaxBytes - Message.MinMessageOverhead - Message.TimestampLength - MessageSet.LogOverhead - 1
     val message2 = new Message(new Array[Byte](safeSize))
     val messageSet2 = new ByteBufferMessageSet(compressionCodec = NoCompressionCodec, messages = message2)
     val response2 = producer.send(produceRequest("test", 0, messageSet2, acks = 1))
@@ -142,14 +142,14 @@ class SyncProducerTest extends KafkaServerTestHarness {
 
     // This message will be dropped silently since message size too large.
     producer.send(produceRequest("test", 0,
-      new ByteBufferMessageSet(compressionCodec = NoCompressionCodec, messages = new Message(new Array[Byte](configs(0).messageMaxBytes + 1))), acks = 0))
+      new ByteBufferMessageSet(compressionCodec = NoCompressionCodec, messages = new Message(new Array[Byte](configs.head.messageMaxBytes + 1))), acks = 0))
 
     // Send another message whose size is large enough to exceed the buffer size so
     // the socket buffer will be flushed immediately;
     // this send should fail since the socket has been closed
     try {
       producer.send(produceRequest("test", 0,
-        new ByteBufferMessageSet(compressionCodec = NoCompressionCodec, messages = new Message(new Array[Byte](configs(0).messageMaxBytes + 1))), acks = 0))
+        new ByteBufferMessageSet(compressionCodec = NoCompressionCodec, messages = new Message(new Array[Byte](configs.head.messageMaxBytes + 1))), acks = 0))
     } catch {
       case e : java.io.IOException => // success
       case e2: Throwable => throw e2
diff --git a/core/src/test/scala/unit/kafka/security/auth/ZkAuthorizationTest.scala b/core/src/test/scala/unit/kafka/security/auth/ZkAuthorizationTest.scala
index bbec5b13d9056..9203130bf20bc 100644
--- a/core/src/test/scala/unit/kafka/security/auth/ZkAuthorizationTest.scala
+++ b/core/src/test/scala/unit/kafka/security/auth/ZkAuthorizationTest.scala
@@ -80,7 +80,7 @@ class ZkAuthorizationTest extends ZooKeeperTestHarness with Logging {
     for (path <- zkUtils.persistentZkPaths) {
       zkUtils.makeSurePersistentPathExists(path)
       if(!path.equals(ZkUtils.ConsumersPath)) {
-        val aclList = (zkUtils.zkConnection.getAcl(path)).getKey
+        val aclList = zkUtils.zkConnection.getAcl(path).getKey
         assertTrue(aclList.size == 2)
         for (acl: ACL <- aclList.asScala) {
           assertTrue(isAclSecure(acl))
@@ -207,15 +207,15 @@ class ZkAuthorizationTest extends ZooKeeperTestHarness with Logging {
     ZkSecurityMigrator.run(Array(s"--zookeeper.acl=$secureOpt", s"--zookeeper.connect=$zkUrl"))
     info("Done with migration")
     for (path <- secondZk.securePersistentZkPaths) {
-      val listParent = (secondZk.zkConnection.getAcl(path)).getKey
+      val listParent = secondZk.zkConnection.getAcl(path).getKey
       assertTrue(path, isAclCorrect(listParent, secondZk.isSecure))
 
       val childPath = path + "/fpjwashere"
-      val listChild = (secondZk.zkConnection.getAcl(childPath)).getKey
+      val listChild = secondZk.zkConnection.getAcl(childPath).getKey
       assertTrue(childPath, isAclCorrect(listChild, secondZk.isSecure))
     }
     // Check consumers path.
-    val consumersAcl = (firstZk.zkConnection.getAcl(ZkUtils.ConsumersPath)).getKey
+    val consumersAcl = firstZk.zkConnection.getAcl(ZkUtils.ConsumersPath).getKey
     assertTrue(ZkUtils.ConsumersPath, isAclCorrect(consumersAcl, false))
   }
 
@@ -223,7 +223,7 @@ class ZkAuthorizationTest extends ZooKeeperTestHarness with Logging {
    * Verifies that the path has the appropriate secure ACL.
    */
   private def verify(path: String): Boolean = {
-    val list = (zkUtils.zkConnection.getAcl(path)).getKey
+    val list = zkUtils.zkConnection.getAcl(path).getKey
     list.asScala.forall(isAclSecure)
   }
 
diff --git a/core/src/test/scala/unit/kafka/server/BaseReplicaFetchTest.scala b/core/src/test/scala/unit/kafka/server/BaseReplicaFetchTest.scala
index c5b61ded051c1..591fcf7642dc1 100644
--- a/core/src/test/scala/unit/kafka/server/BaseReplicaFetchTest.scala
+++ b/core/src/test/scala/unit/kafka/server/BaseReplicaFetchTest.scala
@@ -78,7 +78,7 @@ abstract class BaseReplicaFetchTest extends ZooKeeperTestHarness  {
         val topicAndPart = TopicAndPartition(topic, partition)
         val expectedOffset = brokers.head.getLogManager().getLog(topicAndPart).get.logEndOffset
         result = result && expectedOffset > 0 && brokers.forall { item =>
-          (expectedOffset == item.getLogManager().getLog(topicAndPart).get.logEndOffset)
+          expectedOffset == item.getLogManager().getLog(topicAndPart).get.logEndOffset
         }
       }
       result
diff --git a/core/src/test/scala/unit/kafka/server/DynamicConfigChangeTest.scala b/core/src/test/scala/unit/kafka/server/DynamicConfigChangeTest.scala
index d1ad3a3e2ab14..af979e44767f5 100644
--- a/core/src/test/scala/unit/kafka/server/DynamicConfigChangeTest.scala
+++ b/core/src/test/scala/unit/kafka/server/DynamicConfigChangeTest.scala
@@ -37,7 +37,7 @@ class DynamicConfigChangeTest extends KafkaServerTestHarness {
   @Test
   def testConfigChange() {
     assertTrue("Should contain a ConfigHandler for topics",
-               this.servers(0).dynamicConfigHandlers.contains(ConfigType.Topic))
+               this.servers.head.dynamicConfigHandlers.contains(ConfigType.Topic))
     val oldVal: java.lang.Long = 100000L
     val newVal: java.lang.Long = 200000L
     val tp = TopicAndPartition("test", 0)
@@ -45,21 +45,21 @@ class DynamicConfigChangeTest extends KafkaServerTestHarness {
     logProps.put(LogConfig.FlushMessagesProp, oldVal.toString)
     AdminUtils.createTopic(zkUtils, tp.topic, 1, 1, logProps)
     TestUtils.retry(10000) {
-      val logOpt = this.servers(0).logManager.getLog(tp)
+      val logOpt = this.servers.head.logManager.getLog(tp)
       assertTrue(logOpt.isDefined)
       assertEquals(oldVal, logOpt.get.config.flushInterval)
     }
     logProps.put(LogConfig.FlushMessagesProp, newVal.toString)
     AdminUtils.changeTopicConfig(zkUtils, tp.topic, logProps)
     TestUtils.retry(10000) {
-      assertEquals(newVal, this.servers(0).logManager.getLog(tp).get.config.flushInterval)
+      assertEquals(newVal, this.servers.head.logManager.getLog(tp).get.config.flushInterval)
     }
   }
 
   @Test
   def testClientQuotaConfigChange() {
     assertTrue("Should contain a ConfigHandler for topics",
-               this.servers(0).dynamicConfigHandlers.contains(ConfigType.Client))
+               this.servers.head.dynamicConfigHandlers.contains(ConfigType.Client))
     val clientId = "testClient"
     val props = new Properties()
     props.put(ClientConfigOverride.ProducerOverride, "1000")
@@ -67,8 +67,8 @@ class DynamicConfigChangeTest extends KafkaServerTestHarness {
     AdminUtils.changeClientIdConfig(zkUtils, clientId, props)
 
     TestUtils.retry(10000) {
-      val configHandler = this.servers(0).dynamicConfigHandlers(ConfigType.Client).asInstanceOf[ClientIdConfigHandler]
-      val quotaManagers: Map[Short, ClientQuotaManager] = servers(0).apis.quotaManagers
+      val configHandler = this.servers.head.dynamicConfigHandlers(ConfigType.Client).asInstanceOf[ClientIdConfigHandler]
+      val quotaManagers: Map[Short, ClientQuotaManager] = servers.head.apis.quotaManagers
       val overrideProducerQuota = quotaManagers.get(ApiKeys.PRODUCE.id).get.quota(clientId)
       val overrideConsumerQuota = quotaManagers.get(ApiKeys.FETCH.id).get.quota(clientId)
 
diff --git a/core/src/test/scala/unit/kafka/server/HighwatermarkPersistenceTest.scala b/core/src/test/scala/unit/kafka/server/HighwatermarkPersistenceTest.scala
index 26e28171a409f..f5b515b606e0d 100755
--- a/core/src/test/scala/unit/kafka/server/HighwatermarkPersistenceTest.scala
+++ b/core/src/test/scala/unit/kafka/server/HighwatermarkPersistenceTest.scala
@@ -56,7 +56,7 @@ class HighwatermarkPersistenceTest {
     val metrics = new Metrics
     // create replica manager
     val replicaManager = new ReplicaManager(configs.head, metrics, new MockTime, new JMockTime, zkUtils, scheduler,
-      logManagers(0), new AtomicBoolean(false))
+      logManagers.head, new AtomicBoolean(false))
     replicaManager.startup()
     try {
       replicaManager.checkpointHighWatermarks()
@@ -64,7 +64,7 @@ class HighwatermarkPersistenceTest {
       assertEquals(0L, fooPartition0Hw)
       val partition0 = replicaManager.getOrCreatePartition(topic, 0)
       // create leader and follower replicas
-      val log0 = logManagers(0).createLog(TopicAndPartition(topic, 0), LogConfig())
+      val log0 = logManagers.head.createLog(TopicAndPartition(topic, 0), LogConfig())
       val leaderReplicaPartition0 = new Replica(configs.head.brokerId, partition0, SystemTime, 0, Some(log0))
       partition0.addReplicaIfNotExists(leaderReplicaPartition0)
       val followerReplicaPartition0 = new Replica(configs.last.brokerId, partition0, SystemTime)
@@ -99,7 +99,7 @@ class HighwatermarkPersistenceTest {
     val metrics = new Metrics
     // create replica manager
     val replicaManager = new ReplicaManager(configs.head, metrics, new MockTime(), new JMockTime, zkUtils,
-      scheduler, logManagers(0), new AtomicBoolean(false))
+      scheduler, logManagers.head, new AtomicBoolean(false))
     replicaManager.startup()
     try {
       replicaManager.checkpointHighWatermarks()
@@ -107,7 +107,7 @@ class HighwatermarkPersistenceTest {
       assertEquals(0L, topic1Partition0Hw)
       val topic1Partition0 = replicaManager.getOrCreatePartition(topic1, 0)
       // create leader log
-      val topic1Log0 = logManagers(0).createLog(TopicAndPartition(topic1, 0), LogConfig())
+      val topic1Log0 = logManagers.head.createLog(TopicAndPartition(topic1, 0), LogConfig())
       // create a local replica for topic1
       val leaderReplicaTopic1Partition0 = new Replica(configs.head.brokerId, topic1Partition0, SystemTime, 0, Some(topic1Log0))
       topic1Partition0.addReplicaIfNotExists(leaderReplicaTopic1Partition0)
@@ -123,7 +123,7 @@ class HighwatermarkPersistenceTest {
       // add another partition and set highwatermark
       val topic2Partition0 = replicaManager.getOrCreatePartition(topic2, 0)
       // create leader log
-      val topic2Log0 = logManagers(0).createLog(TopicAndPartition(topic2, 0), LogConfig())
+      val topic2Log0 = logManagers.head.createLog(TopicAndPartition(topic2, 0), LogConfig())
       // create a local replica for topic2
       val leaderReplicaTopic2Partition0 =  new Replica(configs.head.brokerId, topic2Partition0, SystemTime, 0, Some(topic2Log0))
       topic2Partition0.addReplicaIfNotExists(leaderReplicaTopic2Partition0)
@@ -153,7 +153,7 @@ class HighwatermarkPersistenceTest {
   }
 
   def hwmFor(replicaManager: ReplicaManager, topic: String, partition: Int): Long = {
-    replicaManager.highWatermarkCheckpoints(new File(replicaManager.config.logDirs(0)).getAbsolutePath).read.getOrElse(TopicAndPartition(topic, partition), 0L)
+    replicaManager.highWatermarkCheckpoints(new File(replicaManager.config.logDirs.head).getAbsolutePath).read.getOrElse(TopicAndPartition(topic, partition), 0L)
   }
   
 }
diff --git a/core/src/test/scala/unit/kafka/server/ISRExpirationTest.scala b/core/src/test/scala/unit/kafka/server/ISRExpirationTest.scala
index 89a8fd9dc8b48..c34e4f020aabf 100644
--- a/core/src/test/scala/unit/kafka/server/ISRExpirationTest.scala
+++ b/core/src/test/scala/unit/kafka/server/ISRExpirationTest.scala
@@ -126,7 +126,7 @@ class IsrExpirationTest {
     val leaderReplica = partition0.getReplica(configs.head.brokerId).get
 
     // Make the remote replica not read to the end of log. It should be not be out of sync for at least 100 ms
-    for(replica <- (partition0.assignedReplicas() - leaderReplica))
+    for(replica <- partition0.assignedReplicas() - leaderReplica)
       replica.updateLogReadResult(new LogReadResult(FetchDataInfo(new LogOffsetMetadata(10L), MessageSet.Empty), -1L, -1, false))
 
     // Simulate 2 fetch requests spanning more than 100 ms which do not read to the end of the log.
diff --git a/core/src/test/scala/unit/kafka/server/LeaderElectionTest.scala b/core/src/test/scala/unit/kafka/server/LeaderElectionTest.scala
index 72589800e111c..3c30b6bed7902 100755
--- a/core/src/test/scala/unit/kafka/server/LeaderElectionTest.scala
+++ b/core/src/test/scala/unit/kafka/server/LeaderElectionTest.scala
@@ -149,8 +149,7 @@ class LeaderElectionTest extends ZooKeeperTestHarness {
 
       controllerChannelManager.sendRequest(brokerId2, ApiKeys.LEADER_AND_ISR, None, leaderAndIsrRequest,
         staleControllerEpochCallback)
-      TestUtils.waitUntilTrue(() => staleControllerEpochDetected == true,
-        "Controller epoch should be stale")
+      TestUtils.waitUntilTrue(() => staleControllerEpochDetected, "Controller epoch should be stale")
       assertTrue("Stale controller epoch not detected by the broker", staleControllerEpochDetected)
     } finally {
       controllerChannelManager.shutdown()
diff --git a/core/src/test/scala/unit/kafka/server/LogOffsetTest.scala b/core/src/test/scala/unit/kafka/server/LogOffsetTest.scala
index 463cd8a55e2a4..0885709542150 100755
--- a/core/src/test/scala/unit/kafka/server/LogOffsetTest.scala
+++ b/core/src/test/scala/unit/kafka/server/LogOffsetTest.scala
@@ -132,7 +132,7 @@ class LogOffsetTest extends ZooKeeperTestHarness {
       val consumerOffsets =
         simpleConsumer.getOffsetsBefore(offsetRequest).partitionErrorAndOffsets(topicAndPartition).offsets
 
-      if(consumerOffsets(0) == 1) {
+      if(consumerOffsets.head == 1) {
         offsetChanged = true
       }
     }
diff --git a/core/src/test/scala/unit/kafka/server/LogRecoveryTest.scala b/core/src/test/scala/unit/kafka/server/LogRecoveryTest.scala
index d37de761f1385..40ad0f33c181a 100755
--- a/core/src/test/scala/unit/kafka/server/LogRecoveryTest.scala
+++ b/core/src/test/scala/unit/kafka/server/LogRecoveryTest.scala
@@ -55,8 +55,8 @@ class LogRecoveryTest extends ZooKeeperTestHarness {
   val message = "hello"
 
   var producer: KafkaProducer[Integer, String] = null
-  def hwFile1 = new OffsetCheckpoint(new File(configProps1.logDirs(0), ReplicaManager.HighWatermarkFilename))
-  def hwFile2 = new OffsetCheckpoint(new File(configProps2.logDirs(0), ReplicaManager.HighWatermarkFilename))
+  def hwFile1 = new OffsetCheckpoint(new File(configProps1.logDirs.head, ReplicaManager.HighWatermarkFilename))
+  def hwFile2 = new OffsetCheckpoint(new File(configProps2.logDirs.head, ReplicaManager.HighWatermarkFilename))
   var servers = Seq.empty[KafkaServer]
 
   // Some tests restart the brokers then produce more data. But since test brokers use random ports, we need
@@ -95,7 +95,7 @@ class LogRecoveryTest extends ZooKeeperTestHarness {
     producer.close()
     for (server <- servers) {
       server.shutdown()
-      Utils.delete(new File(server.config.logDirs(0)))
+      Utils.delete(new File(server.config.logDirs.head))
     }
     super.tearDown()
   }
diff --git a/core/src/test/scala/unit/kafka/server/ServerGenerateBrokerIdTest.scala b/core/src/test/scala/unit/kafka/server/ServerGenerateBrokerIdTest.scala
index 312edd430f39f..e0b6db4100d5e 100755
--- a/core/src/test/scala/unit/kafka/server/ServerGenerateBrokerIdTest.scala
+++ b/core/src/test/scala/unit/kafka/server/ServerGenerateBrokerIdTest.scala
@@ -177,8 +177,8 @@ class ServerGenerateBrokerIdTest extends ZooKeeperTestHarness {
 
   def verifyBrokerMetadata(logDirs: Seq[String], brokerId: Int): Boolean = {
     for(logDir <- logDirs) {
-      val brokerMetadataOpt = (new BrokerMetadataCheckpoint(
-        new File(logDir + File.separator + brokerMetaPropsFile))).read()
+      val brokerMetadataOpt = new BrokerMetadataCheckpoint(
+        new File(logDir + File.separator + brokerMetaPropsFile)).read()
       brokerMetadataOpt match {
         case Some(brokerMetadata: BrokerMetadata) =>
           if (brokerMetadata.brokerId != brokerId)  return false
diff --git a/core/src/test/scala/unit/kafka/server/SimpleFetchTest.scala b/core/src/test/scala/unit/kafka/server/SimpleFetchTest.scala
index 689b70b4428f4..774169832e976 100644
--- a/core/src/test/scala/unit/kafka/server/SimpleFetchTest.scala
+++ b/core/src/test/scala/unit/kafka/server/SimpleFetchTest.scala
@@ -105,7 +105,7 @@ class SimpleFetchTest {
     val partition = replicaManager.getOrCreatePartition(topic, partitionId)
 
     // create the leader replica with the local log
-    val leaderReplica = new Replica(configs(0).brokerId, partition, time, 0, Some(log))
+    val leaderReplica = new Replica(configs.head.brokerId, partition, time, 0, Some(log))
     leaderReplica.highWatermark = new LogOffsetMetadata(partitionHW)
     partition.leaderReplicaIdOpt = Some(leaderReplica.brokerId)
 
@@ -144,15 +144,15 @@ class SimpleFetchTest {
    */
   @Test
   def testReadFromLog() {
-    val initialTopicCount = BrokerTopicStats.getBrokerTopicStats(topic).totalFetchRequestRate.count();
-    val initialAllTopicsCount = BrokerTopicStats.getBrokerAllTopicsStats().totalFetchRequestRate.count();
+    val initialTopicCount = BrokerTopicStats.getBrokerTopicStats(topic).totalFetchRequestRate.count()
+    val initialAllTopicsCount = BrokerTopicStats.getBrokerAllTopicsStats().totalFetchRequestRate.count()
 
     assertEquals("Reading committed data should return messages only up to high watermark", messagesToHW,
       replicaManager.readFromLocalLog(true, true, fetchInfo).get(topicAndPartition).get.info.messageSet.head.message)
     assertEquals("Reading any data can return messages up to the end of the log", messagesToLEO,
       replicaManager.readFromLocalLog(true, false, fetchInfo).get(topicAndPartition).get.info.messageSet.head.message)
 
-    assertEquals("Counts should increment after fetch", initialTopicCount+2, BrokerTopicStats.getBrokerTopicStats(topic).totalFetchRequestRate.count());
-    assertEquals("Counts should increment after fetch", initialAllTopicsCount+2, BrokerTopicStats.getBrokerAllTopicsStats().totalFetchRequestRate.count());
+    assertEquals("Counts should increment after fetch", initialTopicCount+2, BrokerTopicStats.getBrokerTopicStats(topic).totalFetchRequestRate.count())
+    assertEquals("Counts should increment after fetch", initialAllTopicsCount+2, BrokerTopicStats.getBrokerAllTopicsStats().totalFetchRequestRate.count())
   }
 }
diff --git a/core/src/test/scala/unit/kafka/tools/ConsoleProducerTest.scala b/core/src/test/scala/unit/kafka/tools/ConsoleProducerTest.scala
index 37d334bf01c5d..741eec9917276 100644
--- a/core/src/test/scala/unit/kafka/tools/ConsoleProducerTest.scala
+++ b/core/src/test/scala/unit/kafka/tools/ConsoleProducerTest.scala
@@ -69,10 +69,10 @@ class ConsoleProducerTest {
   @Test
   def testParseKeyProp(): Unit = {
     val config = new ConsoleProducer.ProducerConfig(validArgs)
-    val reader = Class.forName(config.readerClass).newInstance().asInstanceOf[LineMessageReader];
+    val reader = Class.forName(config.readerClass).newInstance().asInstanceOf[LineMessageReader]
     reader.init(System.in,ConsoleProducer.getReaderProps(config))
     assert(reader.keySeparator == "#")
-    assert(reader.parseKey == true)
+    assert(reader.parseKey)
   }
 
 }
diff --git a/core/src/test/scala/unit/kafka/utils/IteratorTemplateTest.scala b/core/src/test/scala/unit/kafka/utils/IteratorTemplateTest.scala
index 56f5905cd1dac..6a40510664526 100644
--- a/core/src/test/scala/unit/kafka/utils/IteratorTemplateTest.scala
+++ b/core/src/test/scala/unit/kafka/utils/IteratorTemplateTest.scala
@@ -22,7 +22,7 @@ import org.junit.{Test, After, Before}
 
 class IteratorTemplateTest extends Assertions {
   
-  val lst = (0 until 10)
+  val lst = 0 until 10
   val iterator = new IteratorTemplate[Int]() {
     var i = 0
     override def makeNext() = {
diff --git a/core/src/test/scala/unit/kafka/utils/JaasTestUtils.scala b/core/src/test/scala/unit/kafka/utils/JaasTestUtils.scala
index 7c4b951e574e9..f39fa6b8cfd1b 100644
--- a/core/src/test/scala/unit/kafka/utils/JaasTestUtils.scala
+++ b/core/src/test/scala/unit/kafka/utils/JaasTestUtils.scala
@@ -51,7 +51,7 @@ object JaasTestUtils {
         entries = Map(
           "username" -> username,
           "password" -> password
-        ) ++ validUsers.map { case (user, pass) => (s"user_$user"-> pass)}
+        ) ++ validUsers.map { case (user, pass) => s"user_$user" -> pass }
       )
     }
   }
diff --git a/core/src/test/scala/unit/kafka/utils/MockScheduler.scala b/core/src/test/scala/unit/kafka/utils/MockScheduler.scala
index 434c22a8c8174..e9dbbb19af856 100644
--- a/core/src/test/scala/unit/kafka/utils/MockScheduler.scala
+++ b/core/src/test/scala/unit/kafka/utils/MockScheduler.scala
@@ -56,7 +56,7 @@ class MockScheduler(val time: Time) extends Scheduler {
   def tick() {
     this synchronized {
       val now = time.milliseconds
-      while(!tasks.isEmpty && tasks.head.nextExecution <= now) {
+      while(tasks.nonEmpty && tasks.head.nextExecution <= now) {
         /* pop and execute the task with the lowest next execution time */
         val curr = tasks.dequeue
         curr.fun()
@@ -78,7 +78,7 @@ class MockScheduler(val time: Time) extends Scheduler {
   
 }
 
-case class MockTask(val name: String, val fun: () => Unit, var nextExecution: Long, val period: Long) extends Ordered[MockTask] {
+case class MockTask(name: String, fun: () => Unit, var nextExecution: Long, period: Long) extends Ordered[MockTask] {
   def periodic = period >= 0
   def compare(t: MockTask): Int = {
     if(t.nextExecution == nextExecution)
diff --git a/core/src/test/scala/unit/kafka/utils/MockTime.scala b/core/src/test/scala/unit/kafka/utils/MockTime.scala
index 0858e04628912..21fb4d9989359 100644
--- a/core/src/test/scala/unit/kafka/utils/MockTime.scala
+++ b/core/src/test/scala/unit/kafka/utils/MockTime.scala
@@ -46,7 +46,7 @@ class MockTime(@volatile private var currentMs: Long) extends Time {
     scheduler.tick()
   }
   
-  override def toString() = "MockTime(%d)".format(milliseconds)
+  override def toString = "MockTime(%d)".format(milliseconds)
 
 }
 
diff --git a/core/src/test/scala/unit/kafka/utils/TestUtils.scala b/core/src/test/scala/unit/kafka/utils/TestUtils.scala
index 7df87fc31c76e..b42a6ba705772 100755
--- a/core/src/test/scala/unit/kafka/utils/TestUtils.scala
+++ b/core/src/test/scala/unit/kafka/utils/TestUtils.scala
@@ -94,7 +94,7 @@ object TestUtils extends Logging {
     val parentFile = new File(parent)
     parentFile.mkdirs()
 
-    org.apache.kafka.test.TestUtils.tempDirectory(parentFile.toPath, "kafka-");
+    org.apache.kafka.test.TestUtils.tempDirectory(parentFile.toPath, "kafka-")
   }
 
   /**
@@ -335,12 +335,12 @@ object TestUtils extends Logging {
 
     // check if the expected iterator is longer
     if (expected.hasNext) {
-      var length1 = length;
+      var length1 = length
       while (expected.hasNext) {
         expected.next
         length1 += 1
       }
-      assertFalse("Iterators have uneven length-- first has more: "+length1 + " > " + length, true);
+      assertFalse("Iterators have uneven length-- first has more: "+length1 + " > " + length, true)
     }
 
     // check if the actual iterator was longer
@@ -350,7 +350,7 @@ object TestUtils extends Logging {
         actual.next
         length2 += 1
       }
-      assertFalse("Iterators have uneven length-- second has more: "+length2 + " > " + length, true);
+      assertFalse("Iterators have uneven length-- second has more: "+length2 + " > " + length, true)
     }
   }
 
@@ -671,7 +671,7 @@ object TestUtils extends Logging {
         try{
           val currentLeaderAndIsrOpt = zkUtils.getLeaderAndIsrForPartition(topic, partition)
           var newLeaderAndIsr: LeaderAndIsr = null
-          if(currentLeaderAndIsrOpt == None)
+          if(currentLeaderAndIsrOpt.isEmpty)
             newLeaderAndIsr = new LeaderAndIsr(leader, List(leader))
           else{
             newLeaderAndIsr = currentLeaderAndIsrOpt.get
@@ -716,7 +716,7 @@ object TestUtils extends Logging {
           } else if (oldLeaderOpt.isDefined && oldLeaderOpt.get != l) {
             trace("Leader for partition [%s,%d] is changed from %d to %d".format(topic, partition, oldLeaderOpt.get, l))
             isLeaderElectedOrChanged = true
-          } else if (!oldLeaderOpt.isDefined) {
+          } else if (oldLeaderOpt.isEmpty) {
             trace("Leader %d is elected for partition [%s,%d]".format(l, topic, partition))
             isLeaderElectedOrChanged = true
           } else {
@@ -856,7 +856,7 @@ object TestUtils extends Logging {
     // in sync replicas should not have any replica that is not in the new assigned replicas
     val phantomInSyncReplicas = inSyncReplicas.toSet -- assignedReplicas.toSet
     assertTrue("All in sync replicas %s must be in the assigned replica list %s".format(inSyncReplicas, assignedReplicas),
-      phantomInSyncReplicas.size == 0)
+      phantomInSyncReplicas.isEmpty)
   }
 
   def ensureNoUnderReplicatedPartitions(zkUtils: ZkUtils, topic: String, partitionToBeReassigned: Int, assignedReplicas: Seq[Int],
@@ -1031,7 +1031,7 @@ object TestUtils extends Logging {
       "Topic path /brokers/topics/%s not deleted after /admin/delete_topic/%s path is deleted".format(topic, topic))
     // ensure that the topic-partition has been deleted from all brokers' replica managers
     TestUtils.waitUntilTrue(() =>
-      servers.forall(server => topicAndPartitions.forall(tp => server.replicaManager.getPartition(tp.topic, tp.partition) == None)),
+      servers.forall(server => topicAndPartitions.forall(tp => server.replicaManager.getPartition(tp.topic, tp.partition).isEmpty)),
       "Replica manager's should have deleted all of this topic's partitions")
     // ensure that logs from all replicas are deleted if delete topic is marked successful in zookeeper
     assertTrue("Replica logs not deleted after delete topic is complete",
@@ -1146,7 +1146,7 @@ class IntEncoder(props: VerifiableProperties = null) extends Encoder[Int] {
 @deprecated("This class is deprecated and it will be removed in a future release.", "0.10.0.0")
 class StaticPartitioner(props: VerifiableProperties = null) extends Partitioner {
   def partition(data: Any, numPartitions: Int): Int = {
-    (data.asInstanceOf[String].length % numPartitions)
+    data.asInstanceOf[String].length % numPartitions
   }
 }