[SPARK-13692][CORE][SQL] Fix trivial Coverity/Checkstyle defects

## What changes were proposed in this pull request?

This issue fixes the following potential bugs and Java coding style detected by Coverity and Checkstyle.

- Implement both null and type checking in equals functions.
- Fix wrong type casting logic in SimpleJavaBean2.equals.
- Add `implement Cloneable` to `UTF8String` and `SortedIterator`.
- Remove dereferencing before null check in `AbstractBytesToBytesMapSuite`.
- Fix coding style: Add '{}' to single `for` statement in mllib examples.
- Remove unused imports in `ColumnarBatch` and `JavaKinesisStreamSuite`.
- Remove unused fields in `ChunkFetchIntegrationSuite`.
- Add `stop()` to prevent resource leak.

Please note that the last two checkstyle errors exist on newly added commits after [SPARK-13583](https://issues.apache.org/jira/browse/SPARK-13583).

## How was this patch tested?

manual via `./dev/lint-java` and Coverity site.

Author: Dongjoon Hyun <dongjoon@apache.org>

Closes #11530 from dongjoon-hyun/SPARK-13692.

1 files changed, 2 insertions, 2 deletions

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 d8af2b336d..61b94b736d 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
@@ -64,7 +64,7 @@ public abstract class AbstractBytesToBytesMapSuite {
 
   private TestMemoryManager memoryManager;
   private TaskMemoryManager taskMemoryManager;
-  private final long PAGE_SIZE_BYTES = 1L << 26; // 64 megabytes
+  private static final long PAGE_SIZE_BYTES = 1L << 26; // 64 megabytes
 
   final LinkedList<File> spillFilesCreated = new LinkedList<File>();
   File tempDir;
@@ -131,8 +131,8 @@ public abstract class AbstractBytesToBytesMapSuite {
     Utils.deleteRecursively(tempDir);
     tempDir = null;
 
-    Assert.assertEquals(0L, taskMemoryManager.cleanUpAllAllocatedMemory());
     if (taskMemoryManager != null) {
+      Assert.assertEquals(0L, taskMemoryManager.cleanUpAllAllocatedMemory());
       long leakedMemory = taskMemoryManager.getMemoryConsumptionForThisTask();
       taskMemoryManager = null;
       Assert.assertEquals(0L, leakedMemory);