[SPARK-13702][CORE][SQL][MLLIB] Use diamond operator for generic instance creation in Java code.

## What changes were proposed in this pull request?

In order to make `docs/examples` (and other related code) more simple/readable/user-friendly, this PR replaces existing codes like the followings by using `diamond` operator.

```
-    final ArrayList<Product2<Object, Object>> dataToWrite =
-      new ArrayList<Product2<Object, Object>>();
+    final ArrayList<Product2<Object, Object>> dataToWrite = new ArrayList<>();
```

Java 7 or higher supports **diamond** operator which replaces the type arguments required to invoke the constructor of a generic class with an empty set of type parameters (<>). Currently, Spark Java code use mixed usage of this.

## How was this patch tested?

Manual.
Pass the existing tests.

Author: Dongjoon Hyun <dongjoon@apache.org>

Closes #11541 from dongjoon-hyun/SPARK-13702.

7 files changed, 17 insertions, 20 deletions

diff --git a/core/src/main/java/org/apache/spark/shuffle/sort/ShuffleExternalSorter.java b/core/src/main/java/org/apache/spark/shuffle/sort/ShuffleExternalSorter.java
index f97e76d7ed..7a114df2d6 100644
--- a/core/src/main/java/org/apache/spark/shuffle/sort/ShuffleExternalSorter.java
+++ b/core/src/main/java/org/apache/spark/shuffle/sort/ShuffleExternalSorter.java
@@ -84,9 +84,9 @@ final class ShuffleExternalSorter extends MemoryConsumer {
    * this might not be necessary if we maintained a pool of re-usable pages in the TaskMemoryManager
    * itself).
    */
-  private final LinkedList<MemoryBlock> allocatedPages = new LinkedList<MemoryBlock>();
+  private final LinkedList<MemoryBlock> allocatedPages = new LinkedList<>();
 
-  private final LinkedList<SpillInfo> spills = new LinkedList<SpillInfo>();
+  private final LinkedList<SpillInfo> spills = new LinkedList<>();
 
   /** Peak memory used by this sorter so far, in bytes. **/
   private long peakMemoryUsedBytes;
diff --git a/core/src/main/java/org/apache/spark/status/api/v1/TaskSorting.java b/core/src/main/java/org/apache/spark/status/api/v1/TaskSorting.java
index f19ed01d5a..0cf84d5f9b 100644
--- a/core/src/main/java/org/apache/spark/status/api/v1/TaskSorting.java
+++ b/core/src/main/java/org/apache/spark/status/api/v1/TaskSorting.java
@@ -29,7 +29,7 @@ public enum TaskSorting {
 
   private final Set<String> alternateNames;
   private TaskSorting(String... names) {
-    alternateNames = new HashSet<String>();
+    alternateNames = new HashSet<>();
     for (String n: names) {
       alternateNames.add(n);
     }
diff --git a/core/src/test/java/org/apache/spark/launcher/SparkLauncherSuite.java b/core/src/test/java/org/apache/spark/launcher/SparkLauncherSuite.java
index 1692df7d30..3e47bfc274 100644
--- a/core/src/test/java/org/apache/spark/launcher/SparkLauncherSuite.java
+++ b/core/src/test/java/org/apache/spark/launcher/SparkLauncherSuite.java
@@ -88,7 +88,7 @@ public class SparkLauncherSuite {
   @Test
   public void testChildProcLauncher() throws Exception {
     SparkSubmitOptionParser opts = new SparkSubmitOptionParser();
-    Map<String, String> env = new HashMap<String, String>();
+    Map<String, String> env = new HashMap<>();
     env.put("SPARK_PRINT_LAUNCH_COMMAND", "1");
 
     SparkLauncher launcher = new SparkLauncher(env)
diff --git a/core/src/test/java/org/apache/spark/shuffle/sort/UnsafeShuffleWriterSuite.java b/core/src/test/java/org/apache/spark/shuffle/sort/UnsafeShuffleWriterSuite.java
index add9d937d3..ddea6f5a69 100644
--- a/core/src/test/java/org/apache/spark/shuffle/sort/UnsafeShuffleWriterSuite.java
+++ b/core/src/test/java/org/apache/spark/shuffle/sort/UnsafeShuffleWriterSuite.java
@@ -67,7 +67,7 @@ public class UnsafeShuffleWriterSuite {
   File mergedOutputFile;
   File tempDir;
   long[] partitionSizesInMergedFile;
-  final LinkedList<File> spillFilesCreated = new LinkedList<File>();
+  final LinkedList<File> spillFilesCreated = new LinkedList<>();
   SparkConf conf;
   final Serializer serializer = new KryoSerializer(new SparkConf());
   TaskMetrics taskMetrics;
@@ -217,7 +217,7 @@ public class UnsafeShuffleWriterSuite {
   }
 
   private List<Tuple2<Object, Object>> readRecordsFromFile() throws IOException {
-    final ArrayList<Tuple2<Object, Object>> recordsList = new ArrayList<Tuple2<Object, Object>>();
+    final ArrayList<Tuple2<Object, Object>> recordsList = new ArrayList<>();
     long startOffset = 0;
     for (int i = 0; i < NUM_PARTITITONS; i++) {
       final long partitionSize = partitionSizesInMergedFile[i];
@@ -286,8 +286,7 @@ public class UnsafeShuffleWriterSuite {
   @Test
   public void writeWithoutSpilling() throws Exception {
     // In this example, each partition should have exactly one record:
-    final ArrayList<Product2<Object, Object>> dataToWrite =
-      new ArrayList<Product2<Object, Object>>();
+    final ArrayList<Product2<Object, Object>> dataToWrite = new ArrayList<>();
     for (int i = 0; i < NUM_PARTITITONS; i++) {
       dataToWrite.add(new Tuple2<Object, Object>(i, i));
     }
@@ -325,8 +324,7 @@ public class UnsafeShuffleWriterSuite {
       conf.set("spark.shuffle.compress", "false");
     }
     final UnsafeShuffleWriter<Object, Object> writer = createWriter(transferToEnabled);
-    final ArrayList<Product2<Object, Object>> dataToWrite =
-      new ArrayList<Product2<Object, Object>>();
+    final ArrayList<Product2<Object, Object>> dataToWrite = new ArrayList<>();
     for (int i : new int[] { 1, 2, 3, 4, 4, 2 }) {
       dataToWrite.add(new Tuple2<Object, Object>(i, i));
     }
@@ -403,7 +401,7 @@ public class UnsafeShuffleWriterSuite {
   public void writeEnoughDataToTriggerSpill() throws Exception {
     memoryManager.limit(PackedRecordPointer.MAXIMUM_PAGE_SIZE_BYTES);
     final UnsafeShuffleWriter<Object, Object> writer = createWriter(false);
-    final ArrayList<Product2<Object, Object>> dataToWrite = new ArrayList<Product2<Object, Object>>();
+    final ArrayList<Product2<Object, Object>> dataToWrite = new ArrayList<>();
     final byte[] bigByteArray = new byte[PackedRecordPointer.MAXIMUM_PAGE_SIZE_BYTES / 10];
     for (int i = 0; i < 10 + 1; i++) {
       dataToWrite.add(new Tuple2<Object, Object>(i, bigByteArray));
@@ -445,8 +443,7 @@ public class UnsafeShuffleWriterSuite {
   @Test
   public void writeRecordsThatAreBiggerThanDiskWriteBufferSize() throws Exception {
     final UnsafeShuffleWriter<Object, Object> writer = createWriter(false);
-    final ArrayList<Product2<Object, Object>> dataToWrite =
-      new ArrayList<Product2<Object, Object>>();
+    final ArrayList<Product2<Object, Object>> dataToWrite = new ArrayList<>();
     final byte[] bytes = new byte[(int) (ShuffleExternalSorter.DISK_WRITE_BUFFER_SIZE * 2.5)];
     new Random(42).nextBytes(bytes);
     dataToWrite.add(new Tuple2<Object, Object>(1, ByteBuffer.wrap(bytes)));
@@ -461,7 +458,7 @@ public class UnsafeShuffleWriterSuite {
   @Test
   public void writeRecordsThatAreBiggerThanMaxRecordSize() throws Exception {
     final UnsafeShuffleWriter<Object, Object> writer = createWriter(false);
-    final ArrayList<Product2<Object, Object>> dataToWrite = new ArrayList<Product2<Object, Object>>();
+    final ArrayList<Product2<Object, Object>> dataToWrite = new ArrayList<>();
     dataToWrite.add(new Tuple2<Object, Object>(1, ByteBuffer.wrap(new byte[1])));
     // We should be able to write a record that's right _at_ the max record size
     final byte[] atMaxRecordSize = new byte[(int) taskMemoryManager.pageSizeBytes() - 4];
@@ -498,7 +495,7 @@ public class UnsafeShuffleWriterSuite {
     taskMemoryManager = spy(taskMemoryManager);
     when(taskMemoryManager.pageSizeBytes()).thenReturn(pageSizeBytes);
     final UnsafeShuffleWriter<Object, Object> writer =
-      new UnsafeShuffleWriter<Object, Object>(
+      new UnsafeShuffleWriter<>(
         blockManager,
         shuffleBlockResolver,
         taskMemoryManager,
diff --git a/core/src/test/java/org/apache/spark/unsafe/map/AbstractBytesToBytesMapSuite.java b/core/src/test/java/org/apache/spark/unsafe/map/AbstractBytesToBytesMapSuite.java
index 61b94b736d..9aab2265c9 100644
--- a/core/src/test/java/org/apache/spark/unsafe/map/AbstractBytesToBytesMapSuite.java
+++ b/core/src/test/java/org/apache/spark/unsafe/map/AbstractBytesToBytesMapSuite.java
@@ -66,7 +66,7 @@ public abstract class AbstractBytesToBytesMapSuite {
   private TaskMemoryManager taskMemoryManager;
   private static final long PAGE_SIZE_BYTES = 1L << 26; // 64 megabytes
 
-  final LinkedList<File> spillFilesCreated = new LinkedList<File>();
+  final LinkedList<File> spillFilesCreated = new LinkedList<>();
   File tempDir;
 
   @Mock(answer = RETURNS_SMART_NULLS) BlockManager blockManager;
@@ -397,7 +397,7 @@ public abstract class AbstractBytesToBytesMapSuite {
     final int size = 65536;
     // Java arrays' hashCodes() aren't based on the arrays' contents, so we need to wrap arrays
     // into ByteBuffers in order to use them as keys here.
-    final Map<ByteBuffer, byte[]> expected = new HashMap<ByteBuffer, byte[]>();
+    final Map<ByteBuffer, byte[]> expected = new HashMap<>();
     final BytesToBytesMap map = new BytesToBytesMap(taskMemoryManager, size, PAGE_SIZE_BYTES);
     try {
       // Fill the map to 90% full so that we can trigger probing
@@ -453,7 +453,7 @@ public abstract class AbstractBytesToBytesMapSuite {
     final BytesToBytesMap map = new BytesToBytesMap(taskMemoryManager, 64, pageSizeBytes);
     // Java arrays' hashCodes() aren't based on the arrays' contents, so we need to wrap arrays
     // into ByteBuffers in order to use them as keys here.
-    final Map<ByteBuffer, byte[]> expected = new HashMap<ByteBuffer, byte[]>();
+    final Map<ByteBuffer, byte[]> expected = new HashMap<>();
     try {
       for (int i = 0; i < 1000; i++) {
         final byte[] key = getRandomByteArray(rand.nextInt(128));
diff --git a/core/src/test/java/org/apache/spark/util/collection/TestTimSort.java b/core/src/test/java/org/apache/spark/util/collection/TestTimSort.java
index 45772b6d3c..e884b1bc12 100644
--- a/core/src/test/java/org/apache/spark/util/collection/TestTimSort.java
+++ b/core/src/test/java/org/apache/spark/util/collection/TestTimSort.java
@@ -76,7 +76,7 @@ public class TestTimSort {
    * @param length The sum of all run lengths that will be added to <code>runs</code>.
    */
   private static List<Long> runsJDKWorstCase(int minRun, int length) {
-    List<Long> runs = new ArrayList<Long>();
+    List<Long> runs = new ArrayList<>();
 
     long runningTotal = 0, Y = minRun + 4, X = minRun;
 
diff --git a/core/src/test/java/org/apache/spark/util/collection/unsafe/sort/UnsafeExternalSorterSuite.java b/core/src/test/java/org/apache/spark/util/collection/unsafe/sort/UnsafeExternalSorterSuite.java
index 492fe49ba4..b757ddc3b3 100644
--- a/core/src/test/java/org/apache/spark/util/collection/unsafe/sort/UnsafeExternalSorterSuite.java
+++ b/core/src/test/java/org/apache/spark/util/collection/unsafe/sort/UnsafeExternalSorterSuite.java
@@ -56,7 +56,7 @@ import static org.mockito.Mockito.*;
 
 public class UnsafeExternalSorterSuite {
 
-  final LinkedList<File> spillFilesCreated = new LinkedList<File>();
+  final LinkedList<File> spillFilesCreated = new LinkedList<>();
   final TestMemoryManager memoryManager =
     new TestMemoryManager(new SparkConf().set("spark.memory.offHeap.enabled", "false"));
   final TaskMemoryManager taskMemoryManager = new TaskMemoryManager(memoryManager, 0);