[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, 4 insertions, 3 deletions

diff --git a/core/src/main/scala/org/apache/spark/SparkContext.scala b/core/src/main/scala/org/apache/spark/SparkContext.scala
index 0e8b735b92..b503c6184a 100644
--- a/core/src/main/scala/org/apache/spark/SparkContext.scala
+++ b/core/src/main/scala/org/apache/spark/SparkContext.scala
@@ -23,8 +23,8 @@ import java.net.URI
 import java.util.{Arrays, Properties, UUID}
 import java.util.concurrent.ConcurrentMap
 import java.util.concurrent.atomic.{AtomicBoolean, AtomicInteger, AtomicReference}
-import java.util.UUID.randomUUID
 
+import scala.annotation.tailrec
 import scala.collection.JavaConverters._
 import scala.collection.Map
 import scala.collection.generic.Growable
@@ -391,8 +391,8 @@ class SparkContext(config: SparkConf) extends Logging with ExecutorAllocationCli
 
     _conf.set("spark.executor.id", SparkContext.DRIVER_IDENTIFIER)
 
-    _jars = _conf.getOption("spark.jars").map(_.split(",")).map(_.filter(_.size != 0)).toSeq.flatten
-    _files = _conf.getOption("spark.files").map(_.split(",")).map(_.filter(_.size != 0))
+    _jars = _conf.getOption("spark.jars").map(_.split(",")).map(_.filter(_.nonEmpty)).toSeq.flatten
+    _files = _conf.getOption("spark.files").map(_.split(",")).map(_.filter(_.nonEmpty))
       .toSeq.flatten
 
     _eventLogDir =
@@ -2310,6 +2310,7 @@ object SparkContext extends Logging {
    * Create a task scheduler based on a given master URL.
    * Return a 2-tuple of the scheduler backend and the task scheduler.
    */
+  @tailrec
   private def createTaskScheduler(
       sc: SparkContext,
       master: String,