[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, 3 insertions, 1 deletions

diff --git a/mllib/src/test/java/org/apache/spark/mllib/fpm/JavaFPGrowthSuite.java b/mllib/src/test/java/org/apache/spark/mllib/fpm/JavaFPGrowthSuite.java
index eeeabfe359..916fff14a7 100644
--- a/mllib/src/test/java/org/apache/spark/mllib/fpm/JavaFPGrowthSuite.java
+++ b/mllib/src/test/java/org/apache/spark/mllib/fpm/JavaFPGrowthSuite.java
@@ -95,7 +95,9 @@ public class JavaFPGrowthSuite implements Serializable {
 
     try {
       model.save(sc.sc(), outputPath);
-      FPGrowthModel newModel = FPGrowthModel.load(sc.sc(), outputPath);
+      @SuppressWarnings("unchecked")
+      FPGrowthModel<String> newModel =
+          (FPGrowthModel<String>) FPGrowthModel.load(sc.sc(), outputPath);
       List<FPGrowth.FreqItemset<String>> freqItemsets = newModel.freqItemsets().toJavaRDD()
         .collect();
       assertEquals(18, freqItemsets.size());