[SPARK-18420][BUILD] Fix the errors caused by lint check in Java

## What changes were proposed in this pull request?

Small fix, fix the errors caused by lint check in Java

- Clear unused objects and `UnusedImports`.
- Add comments around the method `finalize` of `NioBufferedFileInputStream`to turn off checkstyle.
- Cut the line which is longer than 100 characters into two lines.

## How was this patch tested?
Travis CI.
```
$ build/mvn -T 4 -q -DskipTests -Pyarn -Phadoop-2.3 -Pkinesis-asl -Phive -Phive-thriftserver install
$ dev/lint-java
```
Before:
```
Checkstyle checks failed at following occurrences:
[ERROR] src/main/java/org/apache/spark/network/util/TransportConf.java:[21,8] (imports) UnusedImports: Unused import - org.apache.commons.crypto.cipher.CryptoCipherFactory.
[ERROR] src/test/java/org/apache/spark/network/sasl/SparkSaslSuite.java:[516,5] (modifier) RedundantModifier: Redundant 'public' modifier.
[ERROR] src/main/java/org/apache/spark/io/NioBufferedFileInputStream.java:[133] (coding) NoFinalizer: Avoid using finalizer method.
[ERROR] src/main/java/org/apache/spark/sql/catalyst/expressions/UnsafeMapData.java:[71] (sizes) LineLength: Line is longer than 100 characters (found 113).
[ERROR] src/main/java/org/apache/spark/sql/catalyst/expressions/UnsafeArrayData.java:[112] (sizes) LineLength: Line is longer than 100 characters (found 110).
[ERROR] src/test/java/org/apache/spark/sql/catalyst/expressions/HiveHasherSuite.java:[31,17] (modifier) ModifierOrder: 'static' modifier out of order with the JLS suggestions.
[ERROR]src/main/java/org/apache/spark/examples/ml/JavaLogisticRegressionWithElasticNetExample.java:[64] (sizes) LineLength: Line is longer than 100 characters (found 103).
[ERROR] src/main/java/org/apache/spark/examples/ml/JavaInteractionExample.java:[22,8] (imports) UnusedImports: Unused import - org.apache.spark.ml.linalg.Vectors.
[ERROR] src/main/java/org/apache/spark/examples/ml/JavaInteractionExample.java:[51] (regexp) RegexpSingleline: No trailing whitespace allowed.
```

After:
```
$ build/mvn -T 4 -q -DskipTests -Pyarn -Phadoop-2.3 -Pkinesis-asl -Phive -Phive-thriftserver install
$ dev/lint-java
Using `mvn` from path: /home/travis/build/ConeyLiu/spark/build/apache-maven-3.3.9/bin/mvn
Checkstyle checks passed.
```

Author: Xianyang Liu <xyliu0530@icloud.com>

Closes #15865 from ConeyLiu/master.

2 files changed, 3 insertions, 4 deletions

diff --git a/examples/src/main/java/org/apache/spark/examples/ml/JavaInteractionExample.java b/examples/src/main/java/org/apache/spark/examples/ml/JavaInteractionExample.java
index 4213c05703..3684a87e22 100644
--- a/examples/src/main/java/org/apache/spark/examples/ml/JavaInteractionExample.java
+++ b/examples/src/main/java/org/apache/spark/examples/ml/JavaInteractionExample.java
@@ -19,7 +19,6 @@ package org.apache.spark.examples.ml;
 
 import org.apache.spark.ml.feature.Interaction;
 import org.apache.spark.ml.feature.VectorAssembler;
-import org.apache.spark.ml.linalg.Vectors;
 import org.apache.spark.sql.*;
 import org.apache.spark.sql.types.DataTypes;
 import org.apache.spark.sql.types.Metadata;
@@ -48,7 +47,7 @@ public class JavaInteractionExample {
       RowFactory.create(5, 9, 2, 7, 10, 7, 3),
       RowFactory.create(6, 1, 1, 4, 2, 8, 4)
     );
-    
+
     StructType schema = new StructType(new StructField[]{
       new StructField("id1", DataTypes.IntegerType, false, Metadata.empty()),
       new StructField("id2", DataTypes.IntegerType, false, Metadata.empty()),
diff --git a/examples/src/main/java/org/apache/spark/examples/ml/JavaLogisticRegressionWithElasticNetExample.java b/examples/src/main/java/org/apache/spark/examples/ml/JavaLogisticRegressionWithElasticNetExample.java
index b8fb5972ea..4cdec21d23 100644
--- a/examples/src/main/java/org/apache/spark/examples/ml/JavaLogisticRegressionWithElasticNetExample.java
+++ b/examples/src/main/java/org/apache/spark/examples/ml/JavaLogisticRegressionWithElasticNetExample.java
@@ -60,8 +60,8 @@ public class JavaLogisticRegressionWithElasticNetExample {
     LogisticRegressionModel mlrModel = mlr.fit(training);
 
     // Print the coefficients and intercepts for logistic regression with multinomial family
-    System.out.println("Multinomial coefficients: "
-            + lrModel.coefficientMatrix() + "\nMultinomial intercepts: " + mlrModel.interceptVector());
+    System.out.println("Multinomial coefficients: " + lrModel.coefficientMatrix()
+      + "\nMultinomial intercepts: " + mlrModel.interceptVector());
     // $example off$
 
     spark.stop();