[MINOR][MLLIB][SQL] Clean up unused variables and unused import

## What changes were proposed in this pull request?

Clean up unused variables and unused import statements, unnecessary `return` and `toArray`, and some more style improvement,  when I walk through the code examples.

## How was this patch tested?

Testet manually on local laptop.

Author: Xin Ren <iamshrek@126.com>

Closes #14836 from keypointt/codeWalkThroughML.

1 files changed, 4 insertions, 2 deletions

diff --git a/core/src/test/scala/org/apache/spark/AccumulatorSuite.scala b/core/src/test/scala/org/apache/spark/AccumulatorSuite.scala
index 6cbd5ae5d4..6d03ee091e 100644
--- a/core/src/test/scala/org/apache/spark/AccumulatorSuite.scala
+++ b/core/src/test/scala/org/apache/spark/AccumulatorSuite.scala
@@ -100,7 +100,9 @@ class AccumulatorSuite extends SparkFunSuite with Matchers with LocalSparkContex
     val acc: Accumulator[Int] = sc.accumulator(0)
 
     val d = sc.parallelize(1 to 20)
-    an [Exception] should be thrownBy {d.foreach{x => acc.value = x}}
+    intercept[SparkException] {
+      d.foreach(x => acc.value = x)
+    }
   }
 
   test ("add value to collection accumulators") {
@@ -171,7 +173,7 @@ class AccumulatorSuite extends SparkFunSuite with Matchers with LocalSparkContex
       d.foreach {
         x => acc.localValue ++= x
       }
-      acc.value should be ( (0 to maxI).toSet)
+      acc.value should be ((0 to maxI).toSet)
       resetSparkContext()
     }
   }