[SPARK-17359][SQL][MLLIB] Use ArrayBuffer.+=(A) instead of ArrayBuffer.append(A) in performance critical paths

## What changes were proposed in this pull request?

We should generally use `ArrayBuffer.+=(A)` rather than `ArrayBuffer.append(A)`, because `append(A)` would involve extra boxing / unboxing.

## How was this patch tested?

N/A

Author: Liwei Lin <lwlin7@gmail.com>

Closes #14914 from lw-lin/append_to_plus_eq_v2.

1 files changed, 6 insertions, 6 deletions

diff --git a/sql/catalyst/src/test/scala/org/apache/spark/sql/catalyst/trees/TreeNodeSuite.scala b/sql/catalyst/src/test/scala/org/apache/spark/sql/catalyst/trees/TreeNodeSuite.scala
index 6a188e7e55..6246380dbe 100644
--- a/sql/catalyst/src/test/scala/org/apache/spark/sql/catalyst/trees/TreeNodeSuite.scala
+++ b/sql/catalyst/src/test/scala/org/apache/spark/sql/catalyst/trees/TreeNodeSuite.scala
@@ -82,8 +82,8 @@ class TreeNodeSuite extends SparkFunSuite {
     val expected = Seq("+", "1", "*", "2", "-", "3", "4")
     val expression = Add(Literal(1), Multiply(Literal(2), Subtract(Literal(3), Literal(4))))
     expression transformDown {
-      case b: BinaryOperator => actual.append(b.symbol); b
-      case l: Literal => actual.append(l.toString); l
+      case b: BinaryOperator => actual += b.symbol; b
+      case l: Literal => actual += l.toString; l
     }
 
     assert(expected === actual)
@@ -94,8 +94,8 @@ class TreeNodeSuite extends SparkFunSuite {
     val expected = Seq("1", "2", "3", "4", "-", "*", "+")
     val expression = Add(Literal(1), Multiply(Literal(2), Subtract(Literal(3), Literal(4))))
     expression transformUp {
-      case b: BinaryOperator => actual.append(b.symbol); b
-      case l: Literal => actual.append(l.toString); l
+      case b: BinaryOperator => actual += b.symbol; b
+      case l: Literal => actual += l.toString; l
     }
 
     assert(expected === actual)
@@ -134,8 +134,8 @@ class TreeNodeSuite extends SparkFunSuite {
     val expected = Seq("1", "2", "3", "4", "-", "*", "+")
     val expression = Add(Literal(1), Multiply(Literal(2), Subtract(Literal(3), Literal(4))))
     expression foreachUp {
-      case b: BinaryOperator => actual.append(b.symbol);
-      case l: Literal => actual.append(l.toString);
+      case b: BinaryOperator => actual += b.symbol;
+      case l: Literal => actual += l.toString;
     }
 
     assert(expected === actual)