Added note about tree example issue.

Author: jkbradley

examples/src/main/scala/org/apache/spark/examples/ml/DecisionTreeExample.scala

@@ -44,6 +44,13 @@ import org.apache.spark.sql.{SQLContext, DataFrame}
  * {{{
  * ./bin/run-example ml.DecisionTreeExample [options]
  * }}}
+ * Note that Decision Trees can take a large amount of memory.  If the run-example command above
+ * fails, try running via spark-submit and specifying the amount of memory as at least 1g.
+ * For local mode, run
+ * {{{
+ * ./bin/spark-submit --class org.apache.spark.examples.ml.DecisionTreeExample --driver-memory 1g
+ *   [examples JAR path] [options]
+ * }}}
  * If you use it as a template to create your own app, please use `spark-submit` to submit your app.
  */
 object DecisionTreeExample {

mllib/src/main/scala/org/apache/spark/ml/impl/tree/treeParams.scala

@@ -117,7 +117,7 @@ private[ml] trait DecisionTreeParams extends PredictorParams {
   def setMaxDepth(value: Int): this.type = {
     require(value >= 0, s"maxDepth parameter must be >= 0.  Given bad value: $value")
     set(maxDepth, value)
-    this.asInstanceOf[this.type]
+    this
   }
 
   /** @group getParam */