[SPARK-14868][BUILD] Enable NewLineAtEofChecker in checkstyle and fix lint-java errors

## What changes were proposed in this pull request?

Spark uses `NewLineAtEofChecker` rule in Scala by ScalaStyle. And, most Java code also comply with the rule. This PR aims to enforce the same rule `NewlineAtEndOfFile` by CheckStyle explicitly. Also, this fixes lint-java errors since SPARK-14465. The followings are the items.

- Adds a new line at the end of the files (19 files)
- Fixes 25 lint-java errors (12 RedundantModifier, 6 **ArrayTypeStyle**, 2 LineLength, 2 UnusedImports, 2 RegexpSingleline, 1 ModifierOrder)

## How was this patch tested?

After the Jenkins test succeeds, `dev/lint-java` should pass. (Currently, Jenkins dose not run lint-java.)
```bash
$ dev/lint-java
Using `mvn` from path: /usr/local/bin/mvn
Checkstyle checks passed.
```

Author: Dongjoon Hyun <dongjoon@apache.org>

Closes #12632 from dongjoon-hyun/SPARK-14868.

5 files changed, 20 insertions, 21 deletions

diff --git a/core/src/main/java/org/apache/spark/api/java/function/package-info.java b/core/src/main/java/org/apache/spark/api/java/function/package-info.java
index 463a42f233..eefb29aca9 100644
--- a/core/src/main/java/org/apache/spark/api/java/function/package-info.java
+++ b/core/src/main/java/org/apache/spark/api/java/function/package-info.java
@@ -20,4 +20,4 @@
  * these interfaces to pass functions to various Java API methods for Spark. Please visit Spark's
  * Java programming guide for more details.
  */
-package org.apache.spark.api.java.function;
\ No newline at end of file
+package org.apache.spark.api.java.function;
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 c4041a97e8..2be5a16b2d 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
@@ -256,8 +256,8 @@ final class ShuffleExternalSorter extends MemoryConsumer {
     final long spillSize = freeMemory();
     inMemSorter.reset();
     // Reset the in-memory sorter's pointer array only after freeing up the memory pages holding the
-    // records. Otherwise, if the task is over allocated memory, then without freeing the memory pages,
-    // we might not be able to get memory for the pointer array.
+    // records. Otherwise, if the task is over allocated memory, then without freeing the memory
+    // pages, we might not be able to get memory for the pointer array.
     taskContext.taskMetrics().incMemoryBytesSpilled(spillSize);
     return spillSize;
   }
diff --git a/core/src/main/java/org/apache/spark/util/collection/unsafe/sort/PrefixComparators.java b/core/src/main/java/org/apache/spark/util/collection/unsafe/sort/PrefixComparators.java
index 21f2fde79d..c44630fbbc 100644
--- a/core/src/main/java/org/apache/spark/util/collection/unsafe/sort/PrefixComparators.java
+++ b/core/src/main/java/org/apache/spark/util/collection/unsafe/sort/PrefixComparators.java
@@ -22,7 +22,6 @@ import com.google.common.primitives.UnsignedLongs;
 import org.apache.spark.annotation.Private;
 import org.apache.spark.unsafe.types.ByteArray;
 import org.apache.spark.unsafe.types.UTF8String;
-import org.apache.spark.util.Utils;
 
 @Private
 public class PrefixComparators {
@@ -69,7 +68,7 @@ public class PrefixComparators {
    * Provides radix sort parameters. Comparators implementing this also are indicating that the
    * ordering they define is compatible with radix sort.
    */
-  public static abstract class RadixSortSupport extends PrefixComparator {
+  public abstract static class RadixSortSupport extends PrefixComparator {
     /** @return Whether the sort should be descending in binary sort order. */
     public abstract boolean sortDescending();
 
@@ -82,37 +81,37 @@ public class PrefixComparators {
   //
 
   public static final class UnsignedPrefixComparator extends RadixSortSupport {
-    @Override public final boolean sortDescending() { return false; }
-    @Override public final boolean sortSigned() { return false; }
+    @Override public boolean sortDescending() { return false; }
+    @Override public boolean sortSigned() { return false; }
     @Override
-    public final int compare(long aPrefix, long bPrefix) {
+    public int compare(long aPrefix, long bPrefix) {
       return UnsignedLongs.compare(aPrefix, bPrefix);
     }
   }
 
   public static final class UnsignedPrefixComparatorDesc extends RadixSortSupport {
-    @Override public final boolean sortDescending() { return true; }
-    @Override public final boolean sortSigned() { return false; }
+    @Override public boolean sortDescending() { return true; }
+    @Override public boolean sortSigned() { return false; }
     @Override
-    public final int compare(long bPrefix, long aPrefix) {
+    public int compare(long bPrefix, long aPrefix) {
       return UnsignedLongs.compare(aPrefix, bPrefix);
     }
   }
 
   public static final class SignedPrefixComparator extends RadixSortSupport {
-    @Override public final boolean sortDescending() { return false; }
-    @Override public final boolean sortSigned() { return true; }
+    @Override public boolean sortDescending() { return false; }
+    @Override public boolean sortSigned() { return true; }
     @Override
-    public final int compare(long a, long b) {
+    public int compare(long a, long b) {
       return (a < b) ? -1 : (a > b) ? 1 : 0;
     }
   }
 
   public static final class SignedPrefixComparatorDesc extends RadixSortSupport {
-    @Override public final boolean sortDescending() { return true; }
-    @Override public final boolean sortSigned() { return true; }
+    @Override public boolean sortDescending() { return true; }
+    @Override public boolean sortSigned() { return true; }
     @Override
-    public final int compare(long b, long a) {
+    public int compare(long b, long a) {
       return (a < b) ? -1 : (a > b) ? 1 : 0;
     }
   }
diff --git a/core/src/main/java/org/apache/spark/util/collection/unsafe/sort/RadixSort.java b/core/src/main/java/org/apache/spark/util/collection/unsafe/sort/RadixSort.java
index 3357b8e474..4f3f0de7b8 100644
--- a/core/src/main/java/org/apache/spark/util/collection/unsafe/sort/RadixSort.java
+++ b/core/src/main/java/org/apache/spark/util/collection/unsafe/sort/RadixSort.java
@@ -16,7 +16,7 @@
  */
 
 package org.apache.spark.util.collection.unsafe.sort;
- 
+
 import org.apache.spark.unsafe.Platform;
 import org.apache.spark.unsafe.array.LongArray;
 
@@ -227,7 +227,7 @@ public class RadixSort {
     }
     return counts;
   }
-  
+
   /**
    * Specialization of sortAtByte() for key-prefix arrays.
    */
diff --git a/core/src/main/java/org/apache/spark/util/collection/unsafe/sort/UnsafeExternalSorter.java b/core/src/main/java/org/apache/spark/util/collection/unsafe/sort/UnsafeExternalSorter.java
index 3c1cd39dc2..8b6c96a4c4 100644
--- a/core/src/main/java/org/apache/spark/util/collection/unsafe/sort/UnsafeExternalSorter.java
+++ b/core/src/main/java/org/apache/spark/util/collection/unsafe/sort/UnsafeExternalSorter.java
@@ -212,8 +212,8 @@ public final class UnsafeExternalSorter extends MemoryConsumer {
     // written to disk. This also counts the space needed to store the sorter's pointer array.
     inMemSorter.reset();
     // Reset the in-memory sorter's pointer array only after freeing up the memory pages holding the
-    // records. Otherwise, if the task is over allocated memory, then without freeing the memory pages,
-    // we might not be able to get memory for the pointer array.
+    // records. Otherwise, if the task is over allocated memory, then without freeing the memory
+    // pages, we might not be able to get memory for the pointer array.
 
     taskContext.taskMetrics().incMemoryBytesSpilled(spillSize);
     totalSpillBytes += spillSize;