From 153b78f479502112cbae2d92ce0634e659bbc5fd Mon Sep 17 00:00:00 2001
From: Joel Dice <joel.dice@gmail.com>
Date: Thu, 14 Jun 2012 10:55:03 -0600
Subject: [PATCH] fix ArrayList performance issue

The ArrayList(Collection) constructor was allocating two arrays
instead of one due to an off-by-one error in ArrayList.grow.  This
commit fixes that and makes grow and shrink more robust.
---
 classpath/java/util/ArrayList.java | 25 +++++++++++++------------
 test/List.java                     | 15 +++++++++++++++
 2 files changed, 28 insertions(+), 12 deletions(-)

diff --git a/classpath/java/util/ArrayList.java b/classpath/java/util/ArrayList.java
index d7a61d61ed..3935aa44ec 100644
--- a/classpath/java/util/ArrayList.java
+++ b/classpath/java/util/ArrayList.java
@@ -29,14 +29,15 @@ public class ArrayList<T> extends AbstractList<T> implements java.io.Serializabl
     addAll(source);
   }
 
-  private void grow() {
-    if (array == null || size >= array.length) {
-      resize(array == null ? MinimumCapacity : array.length * 2);
+  private void grow(int newSize) {
+    if (array == null || newSize > array.length) {
+      resize(Math.max(newSize, array == null
+                      ? MinimumCapacity : array.length * 2));
     }
   }
 
-  private void shrink() {
-    if (array.length / 2 >= MinimumCapacity && size <= array.length / 3) {
+  private void shrink(int newSize) {
+    if (array.length / 2 >= MinimumCapacity && newSize <= array.length / 3) {
       resize(array.length / 2);
     }
   }
@@ -74,16 +75,15 @@ public class ArrayList<T> extends AbstractList<T> implements java.io.Serializabl
   }
 
   public void add(int index, T element) {
-    size = Math.max(size+1, index+1);
-    grow();
+    int newSize = Math.max(size+1, index+1);
+    grow(newSize);
+    size = newSize;
     System.arraycopy(array, index, array, index+1, size-index-1);
     array[index] = element;
   }
 
   public boolean add(T element) {
-    ++ size;
-    grow();
-    array[size - 1] = element;
+    add(size, element);
     return true;
   }
 
@@ -137,8 +137,9 @@ public class ArrayList<T> extends AbstractList<T> implements java.io.Serializabl
       System.arraycopy(array, index + 1, array, index, size - index);
     }
 
-    -- size;
-    shrink();
+    int newSize = size - 1;
+    shrink(newSize);
+    size = newSize;
 
     return v;
   }
diff --git a/test/List.java b/test/List.java
index 797aefbb7f..c7d73d93fc 100644
--- a/test/List.java
+++ b/test/List.java
@@ -131,6 +131,20 @@ public class List {
     expect(l.size() == 2);
   }
 
+  private static void testGrow() {
+    ArrayList<Integer> foo = new ArrayList<Integer>(2);
+    foo.add(0);
+    foo.add(1);
+    foo.add(2); // first grow
+    foo.add(3);
+    foo.add(4); // second grow
+    foo.add(5);
+
+    for (int i = 0; i < foo.size(); i++) {
+      expect(i == foo.get(i));
+    }
+  }
+
   public static void main(String args[]) {
     ArrayList<Integer> l = new ArrayList<Integer>();
     l.add(1); l.add(2); l.add(3); l.add(4); l.add(5);
@@ -155,5 +169,6 @@ public class List {
 
     testIterators2(new ArrayList());
     testIterators2(new LinkedList());
+    testGrow();
   }
 }