[SPARK-13423][WIP][CORE][SQL][STREAMING] Static analysis fixes for 2.x

## What changes were proposed in this pull request?

Make some cross-cutting code improvements according to static analysis. These are individually up for discussion since they exist in separate commits that can be reverted. The changes are broadly:

- Inner class should be static
- Mismatched hashCode/equals
- Overflow in compareTo
- Unchecked warnings
- Misuse of assert, vs junit.assert
- get(a) + getOrElse(b) -> getOrElse(a,b)
- Array/String .size -> .length (occasionally, -> .isEmpty / .nonEmpty) to avoid implicit conversions
- Dead code
- tailrec
- exists(_ == ) -> contains find + nonEmpty -> exists filter + size -> count
- reduce(_+_) -> sum map + flatten -> map

The most controversial may be .size -> .length simply because of its size. It is intended to avoid implicits that might be expensive in some places.

## How was the this patch tested?

Existing Jenkins unit tests.

Author: Sean Owen <sowen@cloudera.com>

Closes #11292 from srowen/SPARK-13423.

1 files changed, 1 insertions, 1 deletions

diff --git a/common/unsafe/src/test/scala/org/apache/spark/unsafe/types/UTF8StringPropertyCheckSuite.scala b/common/unsafe/src/test/scala/org/apache/spark/unsafe/types/UTF8StringPropertyCheckSuite.scala
index b3bbd68827..8a6b9e3e45 100644
--- a/common/unsafe/src/test/scala/org/apache/spark/unsafe/types/UTF8StringPropertyCheckSuite.scala
+++ b/common/unsafe/src/test/scala/org/apache/spark/unsafe/types/UTF8StringPropertyCheckSuite.scala
@@ -193,7 +193,7 @@ class UTF8StringPropertyCheckSuite extends FunSuite with GeneratorDrivenProperty
 
   test("concat") {
     def concat(orgin: Seq[String]): String =
-      if (orgin.exists(_ == null)) null else orgin.mkString
+      if (orgin.contains(null)) null else orgin.mkString
 
     forAll { (inputs: Seq[String]) =>
       assert(UTF8String.concat(inputs.map(toUTF8): _*) === toUTF8(inputs.mkString))