diff --git a/core/src/main/scala/org/apache/spark/SparkContext.scala b/core/src/main/scala/org/apache/spark/SparkContext.scala
index a9600336f0fe9107e1758397127ad3bacccb47c2..42b2985b50ad79d8399a6ca1216e0c9fdc7b0705 100644
--- a/core/src/main/scala/org/apache/spark/SparkContext.scala
+++ b/core/src/main/scala/org/apache/spark/SparkContext.scala
@@ -24,7 +24,6 @@ import java.util.concurrent.atomic.AtomicInteger
 
 import scala.collection.Map
 import scala.collection.generic.Growable
-import scala.collection.JavaConverters._
 import scala.collection.mutable.ArrayBuffer
 import scala.collection.mutable.HashMap
 
diff --git a/core/src/main/scala/org/apache/spark/deploy/LocalSparkCluster.scala b/core/src/main/scala/org/apache/spark/deploy/LocalSparkCluster.scala
index 308a2bfa222c35531ef024f194a39e4efeec0de4..a7249009431088160fe8659c317e7bcc66c27049 100644
--- a/core/src/main/scala/org/apache/spark/deploy/LocalSparkCluster.scala
+++ b/core/src/main/scala/org/apache/spark/deploy/LocalSparkCluster.scala
@@ -17,12 +17,12 @@
 
 package org.apache.spark.deploy
 
-import akka.actor.{ActorRef, Props, Actor, ActorSystem, Terminated}
+import akka.actor.ActorSystem
 
 import org.apache.spark.deploy.worker.Worker
 import org.apache.spark.deploy.master.Master
-import org.apache.spark.util.{Utils, AkkaUtils}
-import org.apache.spark.{Logging}
+import org.apache.spark.util.Utils
+import org.apache.spark.Logging
 
 import scala.collection.mutable.ArrayBuffer
 
diff --git a/core/src/main/scala/org/apache/spark/executor/CoarseGrainedExecutorBackend.scala b/core/src/main/scala/org/apache/spark/executor/CoarseGrainedExecutorBackend.scala
index caee6b01ab1fa57ae5edb33ab5716cc88fbacf29..8332631838d0aca375fcd1c6e168c2a0dbc9875d 100644
--- a/core/src/main/scala/org/apache/spark/executor/CoarseGrainedExecutorBackend.scala
+++ b/core/src/main/scala/org/apache/spark/executor/CoarseGrainedExecutorBackend.scala
@@ -22,7 +22,7 @@ import java.nio.ByteBuffer
 import akka.actor.{ActorRef, Actor, Props, Terminated}
 import akka.remote.{RemoteClientLifeCycleEvent, RemoteClientShutdown, RemoteClientDisconnected}
 
-import org.apache.spark.{Logging, SparkEnv}
+import org.apache.spark.Logging
 import org.apache.spark.TaskState.TaskState
 import org.apache.spark.scheduler.cluster.CoarseGrainedClusterMessages._
 import org.apache.spark.util.{Utils, AkkaUtils}
diff --git a/core/src/main/scala/org/apache/spark/executor/ExecutorSource.scala b/core/src/main/scala/org/apache/spark/executor/ExecutorSource.scala
index 34ed9c8f73c01cdb5f8c5cd14e32b1df6b010b35..97176e4f5b727c78fbc1a72cdf949df1c8fe8290 100644
--- a/core/src/main/scala/org/apache/spark/executor/ExecutorSource.scala
+++ b/core/src/main/scala/org/apache/spark/executor/ExecutorSource.scala
@@ -20,8 +20,6 @@ package org.apache.spark.executor
 import com.codahale.metrics.{Gauge, MetricRegistry}
 
 import org.apache.hadoop.fs.FileSystem
-import org.apache.hadoop.hdfs.DistributedFileSystem
-import org.apache.hadoop.fs.LocalFileSystem
 
 import scala.collection.JavaConversions._
 
diff --git a/yarn/src/main/scala/org/apache/spark/deploy/yarn/ApplicationMaster.scala b/yarn/src/main/scala/org/apache/spark/deploy/yarn/ApplicationMaster.scala
index 4302ef4cda2619c446608c8cdf47b45d66ecf563..0e47bd7a10a2167fdbb7a367eb779af275d52994 100644
--- a/yarn/src/main/scala/org/apache/spark/deploy/yarn/ApplicationMaster.scala
+++ b/yarn/src/main/scala/org/apache/spark/deploy/yarn/ApplicationMaster.scala
@@ -17,9 +17,8 @@
 
 package org.apache.spark.deploy.yarn
 
-import java.io.IOException;
+import java.io.IOException
 import java.net.Socket
-import java.security.PrivilegedExceptionAction
 import java.util.concurrent.CopyOnWriteArrayList
 import java.util.concurrent.atomic.{AtomicInteger, AtomicReference}
 import org.apache.hadoop.conf.Configuration
@@ -34,7 +33,6 @@ import org.apache.hadoop.yarn.ipc.YarnRPC
 import org.apache.hadoop.yarn.util.{ConverterUtils, Records}
 import org.apache.spark.{SparkContext, Logging}
 import org.apache.spark.util.Utils
-import org.apache.hadoop.security.UserGroupInformation
 import scala.collection.JavaConversions._
 
 class ApplicationMaster(args: ApplicationMasterArguments, conf: Configuration) extends Logging {
@@ -186,8 +184,8 @@ class ApplicationMaster(args: ApplicationMasterArguments, conf: Configuration) e
         var successed = false
         try {
           // Copy
-          var mainArgs: Array[String] = new Array[String](args.userArgs.size())
-          args.userArgs.copyToArray(mainArgs, 0, args.userArgs.size())
+          var mainArgs: Array[String] = new Array[String](args.userArgs.size)
+          args.userArgs.copyToArray(mainArgs, 0, args.userArgs.size)
           mainMethod.invoke(null, mainArgs)
           // some job script has "System.exit(0)" at the end, for example SparkPi, SparkLR
           // userThread will stop here unless it has uncaught exception thrown out
diff --git a/yarn/src/main/scala/org/apache/spark/deploy/yarn/Client.scala b/yarn/src/main/scala/org/apache/spark/deploy/yarn/Client.scala
index 4e0e060ddc29b982947f9dc0669e0c1f742a6e80..c38bdd14ec9c564bf54e6d2c7b02974c2b97a4d6 100644
--- a/yarn/src/main/scala/org/apache/spark/deploy/yarn/Client.scala
+++ b/yarn/src/main/scala/org/apache/spark/deploy/yarn/Client.scala
@@ -22,7 +22,7 @@ import java.nio.ByteBuffer
 
 import org.apache.hadoop.conf.Configuration
 import org.apache.hadoop.fs.{FileContext, FileStatus, FileSystem, Path, FileUtil}
-import org.apache.hadoop.fs.permission.FsPermission;
+import org.apache.hadoop.fs.permission.FsPermission
 import org.apache.hadoop.mapred.Master
 import org.apache.hadoop.net.NetUtils
 import org.apache.hadoop.io.DataOutputBuffer
diff --git a/yarn/src/main/scala/org/apache/spark/deploy/yarn/ClientDistributedCacheManager.scala b/yarn/src/main/scala/org/apache/spark/deploy/yarn/ClientDistributedCacheManager.scala
index 07686fefd7c067bb7753de6eebfce6937a214981..674c8f8112b867e22a09cd94ace0f2fb6d8a62e5 100644
--- a/yarn/src/main/scala/org/apache/spark/deploy/yarn/ClientDistributedCacheManager.scala
+++ b/yarn/src/main/scala/org/apache/spark/deploy/yarn/ClientDistributedCacheManager.scala
@@ -17,7 +17,7 @@
 
 package org.apache.spark.deploy.yarn
 
-import java.net.URI;
+import java.net.URI
 
 import org.apache.hadoop.conf.Configuration
 import org.apache.hadoop.fs.FileStatus
diff --git a/yarn/src/test/scala/org/apache/spark/deploy/yarn/ClientDistributedCacheManagerSuite.scala b/yarn/src/test/scala/org/apache/spark/deploy/yarn/ClientDistributedCacheManagerSuite.scala
index c0a2af0c6faf35cc88f3f770de4e9fb3fe87749c..2941356bc55f9f85ca176c3ef0d23a1a08c6a8e5 100644
--- a/yarn/src/test/scala/org/apache/spark/deploy/yarn/ClientDistributedCacheManagerSuite.scala
+++ b/yarn/src/test/scala/org/apache/spark/deploy/yarn/ClientDistributedCacheManagerSuite.scala
@@ -17,7 +17,7 @@
 
 package org.apache.spark.deploy.yarn
 
-import java.net.URI;
+import java.net.URI
 
 import org.scalatest.FunSuite
 import org.scalatest.mock.MockitoSugar