[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.

3 files changed, 3 insertions, 3 deletions

diff --git a/sql/core/src/main/java/org/apache/spark/sql/execution/datasources/parquet/SpecificParquetRecordReaderBase.java b/sql/core/src/main/java/org/apache/spark/sql/execution/datasources/parquet/SpecificParquetRecordReaderBase.java
index 6bcd155ccd..5c257bc260 100644
--- a/sql/core/src/main/java/org/apache/spark/sql/execution/datasources/parquet/SpecificParquetRecordReaderBase.java
+++ b/sql/core/src/main/java/org/apache/spark/sql/execution/datasources/parquet/SpecificParquetRecordReaderBase.java
@@ -149,7 +149,7 @@ public abstract class SpecificParquetRecordReaderBase<T> extends RecordReader<Vo
    * by MapReduce.
    */
   public static List<String> listDirectory(File path) throws IOException {
-    List<String> result = new ArrayList<String>();
+    List<String> result = new ArrayList<>();
     if (path.isDirectory()) {
       for (File f: path.listFiles()) {
         result.addAll(listDirectory(f));
diff --git a/sql/core/src/test/java/test/org/apache/spark/sql/JavaApplySchemaSuite.java b/sql/core/src/test/java/test/org/apache/spark/sql/JavaApplySchemaSuite.java
index 640efcc737..51f987fda9 100644
--- a/sql/core/src/test/java/test/org/apache/spark/sql/JavaApplySchemaSuite.java
+++ b/sql/core/src/test/java/test/org/apache/spark/sql/JavaApplySchemaSuite.java
@@ -111,7 +111,7 @@ public class JavaApplySchemaSuite implements Serializable {
     df.registerTempTable("people");
     Row[] actual = sqlContext.sql("SELECT * FROM people").collect();
 
-    List<Row> expected = new ArrayList<Row>(2);
+    List<Row> expected = new ArrayList<>(2);
     expected.add(RowFactory.create("Michael", 29));
     expected.add(RowFactory.create("Yin", 28));
 
diff --git a/sql/core/src/test/java/test/org/apache/spark/sql/JavaDatasetSuite.java b/sql/core/src/test/java/test/org/apache/spark/sql/JavaDatasetSuite.java
index 9b624f318c..b054b1095b 100644
--- a/sql/core/src/test/java/test/org/apache/spark/sql/JavaDatasetSuite.java
+++ b/sql/core/src/test/java/test/org/apache/spark/sql/JavaDatasetSuite.java
@@ -67,7 +67,7 @@ public class JavaDatasetSuite implements Serializable {
   }
 
   private <T1, T2> Tuple2<T1, T2> tuple2(T1 t1, T2 t2) {
-    return new Tuple2<T1, T2>(t1, t2);
+    return new Tuple2<>(t1, t2);
   }
 
   @Test