[SPARK-12489][CORE][SQL][MLIB] Fix minor issues found by FindBugs

Include the following changes:

1. Close `java.sql.Statement`
2. Fix incorrect `asInstanceOf`.
3. Remove unnecessary `synchronized` and `ReentrantLock`.

Author: Shixiong Zhu <shixiong@databricks.com>

Closes #10440 from zsxwing/findbugs.

1 files changed, 2 insertions, 2 deletions

diff --git a/mllib/src/main/scala/org/apache/spark/ml/tree/Node.scala b/mllib/src/main/scala/org/apache/spark/ml/tree/Node.scala
index d89682611e..9cfd466294 100644
--- a/mllib/src/main/scala/org/apache/spark/ml/tree/Node.scala
+++ b/mllib/src/main/scala/org/apache/spark/ml/tree/Node.scala
@@ -386,9 +386,9 @@ private[tree] object LearningNode {
     var levelsToGo = indexToLevel(nodeIndex)
     while (levelsToGo > 0) {
       if ((nodeIndex & (1 << levelsToGo - 1)) == 0) {
-        tmpNode = tmpNode.leftChild.asInstanceOf[LearningNode]
+        tmpNode = tmpNode.leftChild.get
       } else {
-        tmpNode = tmpNode.rightChild.asInstanceOf[LearningNode]
+        tmpNode = tmpNode.rightChild.get
       }
       levelsToGo -= 1
     }