[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.

22 files changed, 46 insertions, 4 deletions

diff --git a/examples/src/main/java/org/apache/spark/examples/ml/JavaCountVectorizerExample.java b/examples/src/main/java/org/apache/spark/examples/ml/JavaCountVectorizerExample.java
index ac33adb652..872e5a07d1 100644
--- a/examples/src/main/java/org/apache/spark/examples/ml/JavaCountVectorizerExample.java
+++ b/examples/src/main/java/org/apache/spark/examples/ml/JavaCountVectorizerExample.java
@@ -65,5 +65,7 @@ public class JavaCountVectorizerExample {
 
     cvModel.transform(df).show();
     // $example off$
+
+    jsc.stop();
   }
 }
diff --git a/examples/src/main/java/org/apache/spark/examples/ml/JavaDecisionTreeClassificationExample.java b/examples/src/main/java/org/apache/spark/examples/ml/JavaDecisionTreeClassificationExample.java
index 482225e585..b5347b7650 100644
--- a/examples/src/main/java/org/apache/spark/examples/ml/JavaDecisionTreeClassificationExample.java
+++ b/examples/src/main/java/org/apache/spark/examples/ml/JavaDecisionTreeClassificationExample.java
@@ -95,5 +95,7 @@ public class JavaDecisionTreeClassificationExample {
       (DecisionTreeClassificationModel) (model.stages()[2]);
     System.out.println("Learned classification tree model:\n" + treeModel.toDebugString());
     // $example off$
+
+    jsc.stop();
   }
 }
diff --git a/examples/src/main/java/org/apache/spark/examples/ml/JavaDecisionTreeRegressionExample.java b/examples/src/main/java/org/apache/spark/examples/ml/JavaDecisionTreeRegressionExample.java
index c7f1868dd1..9cb67be04a 100644
--- a/examples/src/main/java/org/apache/spark/examples/ml/JavaDecisionTreeRegressionExample.java
+++ b/examples/src/main/java/org/apache/spark/examples/ml/JavaDecisionTreeRegressionExample.java
@@ -83,5 +83,7 @@ public class JavaDecisionTreeRegressionExample {
       (DecisionTreeRegressionModel) (model.stages()[1]);
     System.out.println("Learned regression tree model:\n" + treeModel.toDebugString());
     // $example off$
+
+    jsc.stop();
   }
 }
diff --git a/examples/src/main/java/org/apache/spark/examples/ml/JavaSQLTransformerExample.java b/examples/src/main/java/org/apache/spark/examples/ml/JavaSQLTransformerExample.java
index d55c70796a..a9d64d5e3f 100644
--- a/examples/src/main/java/org/apache/spark/examples/ml/JavaSQLTransformerExample.java
+++ b/examples/src/main/java/org/apache/spark/examples/ml/JavaSQLTransformerExample.java
@@ -55,5 +55,7 @@ public class JavaSQLTransformerExample {
 
     sqlTrans.transform(df).show();
     // $example off$
+
+    jsc.stop();
   }
 }
diff --git a/examples/src/main/java/org/apache/spark/examples/ml/JavaWord2VecExample.java b/examples/src/main/java/org/apache/spark/examples/ml/JavaWord2VecExample.java
index d472375ca9..a4a05af7c6 100644
--- a/examples/src/main/java/org/apache/spark/examples/ml/JavaWord2VecExample.java
+++ b/examples/src/main/java/org/apache/spark/examples/ml/JavaWord2VecExample.java
@@ -63,5 +63,7 @@ public class JavaWord2VecExample {
       System.out.println(r);
     }
     // $example off$
+
+    jsc.stop();
   }
 }
diff --git a/examples/src/main/java/org/apache/spark/examples/mllib/JavaAssociationRulesExample.java b/examples/src/main/java/org/apache/spark/examples/mllib/JavaAssociationRulesExample.java
index 4d0f989819..189560e3fe 100644
--- a/examples/src/main/java/org/apache/spark/examples/mllib/JavaAssociationRulesExample.java
+++ b/examples/src/main/java/org/apache/spark/examples/mllib/JavaAssociationRulesExample.java
@@ -52,5 +52,7 @@ public class JavaAssociationRulesExample {
         rule.javaAntecedent() + " => " + rule.javaConsequent() + ", " + rule.confidence());
     }
     // $example off$
+
+    sc.stop();
   }
 }
diff --git a/examples/src/main/java/org/apache/spark/examples/mllib/JavaGaussianMixtureExample.java b/examples/src/main/java/org/apache/spark/examples/mllib/JavaGaussianMixtureExample.java
index 4d1c64aa3c..3124411c82 100644
--- a/examples/src/main/java/org/apache/spark/examples/mllib/JavaGaussianMixtureExample.java
+++ b/examples/src/main/java/org/apache/spark/examples/mllib/JavaGaussianMixtureExample.java
@@ -44,8 +44,9 @@ public class JavaGaussianMixtureExample {
         public Vector call(String s) {
           String[] sarray = s.trim().split(" ");
           double[] values = new double[sarray.length];
-          for (int i = 0; i < sarray.length; i++)
+          for (int i = 0; i < sarray.length; i++) {
             values[i] = Double.parseDouble(sarray[i]);
+          }
           return Vectors.dense(values);
         }
       }
diff --git a/examples/src/main/java/org/apache/spark/examples/mllib/JavaGradientBoostingClassificationExample.java b/examples/src/main/java/org/apache/spark/examples/mllib/JavaGradientBoostingClassificationExample.java
index 80faabd232..0c2e4c928b 100644
--- a/examples/src/main/java/org/apache/spark/examples/mllib/JavaGradientBoostingClassificationExample.java
+++ b/examples/src/main/java/org/apache/spark/examples/mllib/JavaGradientBoostingClassificationExample.java
@@ -87,6 +87,8 @@ public class JavaGradientBoostingClassificationExample {
     GradientBoostedTreesModel sameModel = GradientBoostedTreesModel.load(jsc.sc(),
       "target/tmp/myGradientBoostingClassificationModel");
     // $example off$
+
+    jsc.stop();
   }
 
 }
diff --git a/examples/src/main/java/org/apache/spark/examples/mllib/JavaGradientBoostingRegressionExample.java b/examples/src/main/java/org/apache/spark/examples/mllib/JavaGradientBoostingRegressionExample.java
index 216895b368..c1bc2098dc 100644
--- a/examples/src/main/java/org/apache/spark/examples/mllib/JavaGradientBoostingRegressionExample.java
+++ b/examples/src/main/java/org/apache/spark/examples/mllib/JavaGradientBoostingRegressionExample.java
@@ -92,5 +92,7 @@ public class JavaGradientBoostingRegressionExample {
     GradientBoostedTreesModel sameModel = GradientBoostedTreesModel.load(jsc.sc(),
       "target/tmp/myGradientBoostingRegressionModel");
     // $example off$
+
+    jsc.stop();
   }
 }
diff --git a/examples/src/main/java/org/apache/spark/examples/mllib/JavaIsotonicRegressionExample.java b/examples/src/main/java/org/apache/spark/examples/mllib/JavaIsotonicRegressionExample.java
index 37e709b4cb..e632e35110 100644
--- a/examples/src/main/java/org/apache/spark/examples/mllib/JavaIsotonicRegressionExample.java
+++ b/examples/src/main/java/org/apache/spark/examples/mllib/JavaIsotonicRegressionExample.java
@@ -82,5 +82,7 @@ public class JavaIsotonicRegressionExample {
     model.save(jsc.sc(), "target/tmp/myIsotonicRegressionModel");
     IsotonicRegressionModel sameModel = IsotonicRegressionModel.load(jsc.sc(), "target/tmp/myIsotonicRegressionModel");
     // $example off$
+
+    jsc.stop();
   }
 }
diff --git a/examples/src/main/java/org/apache/spark/examples/mllib/JavaKMeansExample.java b/examples/src/main/java/org/apache/spark/examples/mllib/JavaKMeansExample.java
index a24606a2e9..006d96d111 100644
--- a/examples/src/main/java/org/apache/spark/examples/mllib/JavaKMeansExample.java
+++ b/examples/src/main/java/org/apache/spark/examples/mllib/JavaKMeansExample.java
@@ -44,8 +44,9 @@ public class JavaKMeansExample {
         public Vector call(String s) {
           String[] sarray = s.split(" ");
           double[] values = new double[sarray.length];
-          for (int i = 0; i < sarray.length; i++)
+          for (int i = 0; i < sarray.length; i++) {
             values[i] = Double.parseDouble(sarray[i]);
+          }
           return Vectors.dense(values);
         }
       }
diff --git a/examples/src/main/java/org/apache/spark/examples/mllib/JavaLatentDirichletAllocationExample.java b/examples/src/main/java/org/apache/spark/examples/mllib/JavaLatentDirichletAllocationExample.java
index 4d8b65c544..578564eeb2 100644
--- a/examples/src/main/java/org/apache/spark/examples/mllib/JavaLatentDirichletAllocationExample.java
+++ b/examples/src/main/java/org/apache/spark/examples/mllib/JavaLatentDirichletAllocationExample.java
@@ -49,8 +49,9 @@ public class JavaLatentDirichletAllocationExample {
         public Vector call(String s) {
           String[] sarray = s.trim().split(" ");
           double[] values = new double[sarray.length];
-          for (int i = 0; i < sarray.length; i++)
+          for (int i = 0; i < sarray.length; i++) {
             values[i] = Double.parseDouble(sarray[i]);
+          }
           return Vectors.dense(values);
         }
       }
diff --git a/examples/src/main/java/org/apache/spark/examples/mllib/JavaMultiLabelClassificationMetricsExample.java b/examples/src/main/java/org/apache/spark/examples/mllib/JavaMultiLabelClassificationMetricsExample.java
index 4717155438..5904260e2d 100644
--- a/examples/src/main/java/org/apache/spark/examples/mllib/JavaMultiLabelClassificationMetricsExample.java
+++ b/examples/src/main/java/org/apache/spark/examples/mllib/JavaMultiLabelClassificationMetricsExample.java
@@ -74,5 +74,7 @@ public class JavaMultiLabelClassificationMetricsExample {
     // Subset accuracy
     System.out.format("Subset accuracy = %f\n", metrics.subsetAccuracy());
     // $example off$
+
+    sc.stop();
   }
 }
diff --git a/examples/src/main/java/org/apache/spark/examples/mllib/JavaNaiveBayesExample.java b/examples/src/main/java/org/apache/spark/examples/mllib/JavaNaiveBayesExample.java
index e6a5904bd7..478e615123 100644
--- a/examples/src/main/java/org/apache/spark/examples/mllib/JavaNaiveBayesExample.java
+++ b/examples/src/main/java/org/apache/spark/examples/mllib/JavaNaiveBayesExample.java
@@ -60,5 +60,7 @@ public class JavaNaiveBayesExample {
     model.save(jsc.sc(), "target/tmp/myNaiveBayesModel");
     NaiveBayesModel sameModel = NaiveBayesModel.load(jsc.sc(), "target/tmp/myNaiveBayesModel");
     // $example off$
+
+    jsc.stop();
   }
 }
diff --git a/examples/src/main/java/org/apache/spark/examples/mllib/JavaPrefixSpanExample.java b/examples/src/main/java/org/apache/spark/examples/mllib/JavaPrefixSpanExample.java
index 68ec7c1e6e..1634075941 100644
--- a/examples/src/main/java/org/apache/spark/examples/mllib/JavaPrefixSpanExample.java
+++ b/examples/src/main/java/org/apache/spark/examples/mllib/JavaPrefixSpanExample.java
@@ -51,5 +51,7 @@ public class JavaPrefixSpanExample {
       System.out.println(freqSeq.javaSequence() + ", " + freqSeq.freq());
     }
     // $example off$
+
+    sc.stop();
   }
 }
diff --git a/examples/src/main/java/org/apache/spark/examples/mllib/JavaRandomForestClassificationExample.java b/examples/src/main/java/org/apache/spark/examples/mllib/JavaRandomForestClassificationExample.java
index 9219eef1ad..f4c9d8a35d 100644
--- a/examples/src/main/java/org/apache/spark/examples/mllib/JavaRandomForestClassificationExample.java
+++ b/examples/src/main/java/org/apache/spark/examples/mllib/JavaRandomForestClassificationExample.java
@@ -85,5 +85,7 @@ public class JavaRandomForestClassificationExample {
     RandomForestModel sameModel = RandomForestModel.load(jsc.sc(),
       "target/tmp/myRandomForestClassificationModel");
     // $example off$
+
+    jsc.stop();
   }
 }
diff --git a/examples/src/main/java/org/apache/spark/examples/mllib/JavaRandomForestRegressionExample.java b/examples/src/main/java/org/apache/spark/examples/mllib/JavaRandomForestRegressionExample.java
index 4db926a421..c71125ce41 100644
--- a/examples/src/main/java/org/apache/spark/examples/mllib/JavaRandomForestRegressionExample.java
+++ b/examples/src/main/java/org/apache/spark/examples/mllib/JavaRandomForestRegressionExample.java
@@ -91,5 +91,7 @@ public class JavaRandomForestRegressionExample {
     RandomForestModel sameModel = RandomForestModel.load(jsc.sc(),
       "target/tmp/myRandomForestRegressionModel");
     // $example off$
+
+    jsc.stop();
   }
 }
diff --git a/examples/src/main/java/org/apache/spark/examples/mllib/JavaRankingMetricsExample.java b/examples/src/main/java/org/apache/spark/examples/mllib/JavaRankingMetricsExample.java
index 4ad2104763..54dfc404ca 100644
--- a/examples/src/main/java/org/apache/spark/examples/mllib/JavaRankingMetricsExample.java
+++ b/examples/src/main/java/org/apache/spark/examples/mllib/JavaRankingMetricsExample.java
@@ -181,5 +181,7 @@ public class JavaRankingMetricsExample {
     // R-squared
     System.out.format("R-squared = %f\n", regressionMetrics.r2());
     // $example off$
+
+    sc.stop();
   }
 }
diff --git a/examples/src/main/java/org/apache/spark/examples/mllib/JavaRecommendationExample.java b/examples/src/main/java/org/apache/spark/examples/mllib/JavaRecommendationExample.java
index c179e7578c..5e643420ad 100644
--- a/examples/src/main/java/org/apache/spark/examples/mllib/JavaRecommendationExample.java
+++ b/examples/src/main/java/org/apache/spark/examples/mllib/JavaRecommendationExample.java
@@ -93,5 +93,7 @@ public class JavaRecommendationExample {
     MatrixFactorizationModel sameModel = MatrixFactorizationModel.load(jsc.sc(),
       "target/tmp/myCollaborativeFilter");
     // $example off$
+
+    jsc.stop();
   }
 }
diff --git a/examples/src/main/java/org/apache/spark/examples/mllib/JavaRegressionMetricsExample.java b/examples/src/main/java/org/apache/spark/examples/mllib/JavaRegressionMetricsExample.java
index 4e89dd0c37..b3e5c04759 100644
--- a/examples/src/main/java/org/apache/spark/examples/mllib/JavaRegressionMetricsExample.java
+++ b/examples/src/main/java/org/apache/spark/examples/mllib/JavaRegressionMetricsExample.java
@@ -88,5 +88,7 @@ public class JavaRegressionMetricsExample {
     LinearRegressionModel sameModel = LinearRegressionModel.load(sc.sc(),
       "target/tmp/LogisticRegressionModel");
     // $example off$
+
+    sc.stop();
   }
 }
diff --git a/examples/src/main/java/org/apache/spark/examples/mllib/JavaSVDExample.java b/examples/src/main/java/org/apache/spark/examples/mllib/JavaSVDExample.java
index f3685db9f2..b417da8f85 100644
--- a/examples/src/main/java/org/apache/spark/examples/mllib/JavaSVDExample.java
+++ b/examples/src/main/java/org/apache/spark/examples/mllib/JavaSVDExample.java
@@ -40,6 +40,7 @@ public class JavaSVDExample {
   public static void main(String[] args) {
     SparkConf conf = new SparkConf().setAppName("SVD Example");
     SparkContext sc = new SparkContext(conf);
+    JavaSparkContext jsc = JavaSparkContext.fromSparkContext(sc);
 
     // $example on$
     double[][] array = {{1.12, 2.05, 3.12}, {5.56, 6.28, 8.94}, {10.2, 8.0, 20.5}};
@@ -48,7 +49,7 @@ public class JavaSVDExample {
       Vector currentRow = Vectors.dense(array[i]);
       rowsList.add(currentRow);
     }
-    JavaRDD<Vector> rows = JavaSparkContext.fromSparkContext(sc).parallelize(rowsList);
+    JavaRDD<Vector> rows = jsc.parallelize(rowsList);
 
     // Create a RowMatrix from JavaRDD<Vector>.
     RowMatrix mat = new RowMatrix(rows.rdd());
@@ -66,5 +67,7 @@ public class JavaSVDExample {
     }
     System.out.println("Singular values are: " + s);
     System.out.println("V factor is:\n" + V);
+
+    jsc.stop();
   }
 }
diff --git a/examples/src/main/java/org/apache/spark/examples/mllib/JavaSimpleFPGrowth.java b/examples/src/main/java/org/apache/spark/examples/mllib/JavaSimpleFPGrowth.java
index 72edaca5e9..7f4fe60042 100644
--- a/examples/src/main/java/org/apache/spark/examples/mllib/JavaSimpleFPGrowth.java
+++ b/examples/src/main/java/org/apache/spark/examples/mllib/JavaSimpleFPGrowth.java
@@ -67,5 +67,7 @@ public class JavaSimpleFPGrowth {
         rule.javaAntecedent() + " => " + rule.javaConsequent() + ", " + rule.confidence());
     }
     // $example off$
+
+    sc.stop();
   }
 }