[SPARK-17331][FOLLOWUP][ML][CORE] Avoid allocating 0-length arrays

## What changes were proposed in this pull request?

`Array[T]()` -> `Array.empty[T]` to avoid allocating 0-length arrays.
Use regex `find . -name '*.scala' | xargs -i bash -c 'egrep "Array\[[A-Za-z]+\]\(\)" -n {} && echo {}'` to find modification candidates.

cc srowen

## How was this patch tested?
existing tests

Author: Zheng RuiFeng <ruifengz@foxmail.com>

Closes #15564 from zhengruifeng/avoid_0_length_array.

6 files changed, 7 insertions, 7 deletions

diff --git a/core/src/test/scala/org/apache/spark/CheckpointSuite.scala b/core/src/test/scala/org/apache/spark/CheckpointSuite.scala
index 9f94e36324..b117c7709b 100644
--- a/core/src/test/scala/org/apache/spark/CheckpointSuite.scala
+++ b/core/src/test/scala/org/apache/spark/CheckpointSuite.scala
@@ -500,7 +500,7 @@ class CheckpointSuite extends SparkFunSuite with RDDCheckpointTester with LocalS
   }
 
   runTest("CheckpointRDD with zero partitions") { reliableCheckpoint: Boolean =>
-    val rdd = new BlockRDD[Int](sc, Array[BlockId]())
+    val rdd = new BlockRDD[Int](sc, Array.empty[BlockId])
     assert(rdd.partitions.size === 0)
     assert(rdd.isCheckpointed === false)
     assert(rdd.isCheckpointedAndMaterialized === false)
diff --git a/core/src/test/scala/org/apache/spark/deploy/JsonProtocolSuite.scala b/core/src/test/scala/org/apache/spark/deploy/JsonProtocolSuite.scala
index 2d48e75cfb..7093dad05c 100644
--- a/core/src/test/scala/org/apache/spark/deploy/JsonProtocolSuite.scala
+++ b/core/src/test/scala/org/apache/spark/deploy/JsonProtocolSuite.scala
@@ -65,7 +65,7 @@ class JsonProtocolSuite extends SparkFunSuite with JsonTestUtils {
   test("writeMasterState") {
     val workers = Array(createWorkerInfo(), createWorkerInfo())
     val activeApps = Array(createAppInfo())
-    val completedApps = Array[ApplicationInfo]()
+    val completedApps = Array.empty[ApplicationInfo]
     val activeDrivers = Array(createDriverInfo())
     val completedDrivers = Array(createDriverInfo())
     val stateResponse = new MasterStateResponse(
diff --git a/core/src/test/scala/org/apache/spark/deploy/SparkSubmitSuite.scala b/core/src/test/scala/org/apache/spark/deploy/SparkSubmitSuite.scala
index 732cbfaaee..7c649e305a 100644
--- a/core/src/test/scala/org/apache/spark/deploy/SparkSubmitSuite.scala
+++ b/core/src/test/scala/org/apache/spark/deploy/SparkSubmitSuite.scala
@@ -91,7 +91,7 @@ class SparkSubmitSuite
 
   // scalastyle:off println
   test("prints usage on empty input") {
-    testPrematureExit(Array[String](), "Usage: spark-submit")
+    testPrematureExit(Array.empty[String], "Usage: spark-submit")
   }
 
   test("prints usage with only --help") {
diff --git a/core/src/test/scala/org/apache/spark/deploy/history/HistoryServerArgumentsSuite.scala b/core/src/test/scala/org/apache/spark/deploy/history/HistoryServerArgumentsSuite.scala
index 34f27ecaa0..de321db845 100644
--- a/core/src/test/scala/org/apache/spark/deploy/history/HistoryServerArgumentsSuite.scala
+++ b/core/src/test/scala/org/apache/spark/deploy/history/HistoryServerArgumentsSuite.scala
@@ -33,7 +33,7 @@ class HistoryServerArgumentsSuite extends SparkFunSuite {
     .set("spark.testing", "true")
 
   test("No Arguments Parsing") {
-    val argStrings = Array[String]()
+    val argStrings = Array.empty[String]
     val hsa = new HistoryServerArguments(conf, argStrings)
     assert(conf.get("spark.history.fs.logDirectory") === logDir.getAbsolutePath)
     assert(conf.get("spark.history.fs.updateInterval") === "1")
diff --git a/core/src/test/scala/org/apache/spark/io/ChunkedByteBufferSuite.scala b/core/src/test/scala/org/apache/spark/io/ChunkedByteBufferSuite.scala
index 38b48a4c9e..3b798e36b0 100644
--- a/core/src/test/scala/org/apache/spark/io/ChunkedByteBufferSuite.scala
+++ b/core/src/test/scala/org/apache/spark/io/ChunkedByteBufferSuite.scala
@@ -57,7 +57,7 @@ class ChunkedByteBufferSuite extends SparkFunSuite {
   }
 
   test("toArray()") {
-    val empty = ByteBuffer.wrap(Array[Byte]())
+    val empty = ByteBuffer.wrap(Array.empty[Byte])
     val bytes = ByteBuffer.wrap(Array.tabulate(8)(_.toByte))
     val chunkedByteBuffer = new ChunkedByteBuffer(Array(bytes, bytes, empty))
     assert(chunkedByteBuffer.toArray === bytes.array() ++ bytes.array())
@@ -74,7 +74,7 @@ class ChunkedByteBufferSuite extends SparkFunSuite {
   }
 
   test("toInputStream()") {
-    val empty = ByteBuffer.wrap(Array[Byte]())
+    val empty = ByteBuffer.wrap(Array.empty[Byte])
     val bytes1 = ByteBuffer.wrap(Array.tabulate(256)(_.toByte))
     val bytes2 = ByteBuffer.wrap(Array.tabulate(128)(_.toByte))
     val chunkedByteBuffer = new ChunkedByteBuffer(Array(empty, bytes1, bytes2))
diff --git a/core/src/test/scala/org/apache/spark/serializer/KryoSerializerSuite.scala b/core/src/test/scala/org/apache/spark/serializer/KryoSerializerSuite.scala
index 57a8231200..bc6e98365d 100644
--- a/core/src/test/scala/org/apache/spark/serializer/KryoSerializerSuite.scala
+++ b/core/src/test/scala/org/apache/spark/serializer/KryoSerializerSuite.scala
@@ -100,7 +100,7 @@ class KryoSerializerSuite extends SparkFunSuite with SharedSparkContext {
     check(Array("aaa", "bbb", null))
     check(Array(true, false, true))
     check(Array('a', 'b', 'c'))
-    check(Array[Int]())
+    check(Array.empty[Int])
     check(Array(Array("1", "2"), Array("1", "2", "3", "4")))
   }