[SPARK-17682][SQL] Mark children as final for unary, binary, leaf expressions and plan nodes

## What changes were proposed in this pull request?
This patch marks the children method as final in unary, binary, and leaf expressions and plan nodes (both logical plan and physical plan), as brought up in http://apache-spark-developers-list.1001551.n3.nabble.com/Should-LeafExpression-have-children-final-override-like-Nondeterministic-td19104.html

## How was this patch tested?
This is a simple modifier change and has no impact on test coverage.

Author: Reynold Xin <rxin@databricks.com>

Closes #15256 from rxin/SPARK-17682.

1 files changed, 3 insertions, 3 deletions

diff --git a/sql/core/src/main/scala/org/apache/spark/sql/execution/SparkPlan.scala b/sql/core/src/main/scala/org/apache/spark/sql/execution/SparkPlan.scala
index 6aeefa6edd..48d6ef6dcd 100644
--- a/sql/core/src/main/scala/org/apache/spark/sql/execution/SparkPlan.scala
+++ b/sql/core/src/main/scala/org/apache/spark/sql/execution/SparkPlan.scala
@@ -380,7 +380,7 @@ object SparkPlan {
 }
 
 trait LeafExecNode extends SparkPlan {
-  override def children: Seq[SparkPlan] = Nil
+  override final def children: Seq[SparkPlan] = Nil
   override def producedAttributes: AttributeSet = outputSet
 }
 
@@ -394,7 +394,7 @@ object UnaryExecNode {
 trait UnaryExecNode extends SparkPlan {
   def child: SparkPlan
 
-  override def children: Seq[SparkPlan] = child :: Nil
+  override final def children: Seq[SparkPlan] = child :: Nil
 
   override def outputPartitioning: Partitioning = child.outputPartitioning
 }
@@ -403,5 +403,5 @@ trait BinaryExecNode extends SparkPlan {
   def left: SparkPlan
   def right: SparkPlan
 
-  override def children: Seq[SparkPlan] = Seq(left, right)
+  override final def children: Seq[SparkPlan] = Seq(left, right)
 }