[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.

2 files changed, 7 insertions, 2 deletions

diff --git a/sql/core/src/main/java/org/apache/spark/sql/execution/vectorized/ColumnarBatch.java b/sql/core/src/main/java/org/apache/spark/sql/execution/vectorized/ColumnarBatch.java
index 18763672c6..9a8aedfa56 100644
--- a/sql/core/src/main/java/org/apache/spark/sql/execution/vectorized/ColumnarBatch.java
+++ b/sql/core/src/main/java/org/apache/spark/sql/execution/vectorized/ColumnarBatch.java
@@ -22,7 +22,6 @@ import java.util.Iterator;
 import org.apache.commons.lang.NotImplementedException;
 
 import org.apache.spark.memory.MemoryMode;
-import org.apache.spark.sql.Column;
 import org.apache.spark.sql.catalyst.InternalRow;
 import org.apache.spark.sql.catalyst.expressions.GenericMutableRow;
 import org.apache.spark.sql.catalyst.expressions.UnsafeRow;
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 e0e56f3fbf..9b624f318c 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
@@ -465,6 +465,9 @@ public class JavaDatasetSuite implements Serializable {
 
     @Override
     public boolean equals(Object other) {
+      if (this == other) return true;
+      if (other == null || getClass() != other.getClass()) return false;
+
       return this.value.equals(((KryoSerializable) other).value);
     }
 
@@ -483,6 +486,9 @@ public class JavaDatasetSuite implements Serializable {
 
     @Override
     public boolean equals(Object other) {
+      if (this == other) return true;
+      if (other == null || getClass() != other.getClass()) return false;
+
       return this.value.equals(((JavaSerializable) other).value);
     }
 
@@ -631,7 +637,7 @@ public class JavaDatasetSuite implements Serializable {
       if (this == o) return true;
       if (o == null || getClass() != o.getClass()) return false;
 
-      SimpleJavaBean that = (SimpleJavaBean) o;
+      SimpleJavaBean2 that = (SimpleJavaBean2) o;
 
       if (!a.equals(that.a)) return false;
       if (!b.equals(that.b)) return false;