[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/yarn/src/test/scala/org/apache/spark/deploy/yarn/ClientSuite.scala b/yarn/src/test/scala/org/apache/spark/deploy/yarn/ClientSuite.scala
index 998bd1377d..19065373c6 100644
--- a/yarn/src/test/scala/org/apache/spark/deploy/yarn/ClientSuite.scala
+++ b/yarn/src/test/scala/org/apache/spark/deploy/yarn/ClientSuite.scala
@@ -213,7 +213,7 @@ class ClientSuite extends SparkFunSuite with Matchers with BeforeAndAfterAll
     appContext.getClass.getMethods.filter(_.getName.equals("getApplicationTags")).foreach{ method =>
       val tags = method.invoke(appContext).asInstanceOf[java.util.Set[String]]
       tags should contain allOf ("tag1", "dup", "tag2", "multi word")
-      tags.asScala.filter(_.nonEmpty).size should be (4)
+      tags.asScala.count(_.nonEmpty) should be (4)
     }
     appContext.getMaxAppAttempts should be (42)
   }