--- jsr166/src/main/java/util/ArrayList.java	2019/08/10 16:48:05	1.68
+++ jsr166/src/main/java/util/ArrayList.java	2020/07/24 20:57:26	1.71
@@ -109,6 +109,7 @@ import jdk.internal.util.ArraysSupport;
 public class ArrayList<E> extends AbstractList<E>
         implements List<E>, RandomAccess, Cloneable, java.io.Serializable
 {
+    // OPENJDK @java.io.Serial
     private static final long serialVersionUID = 8683452581122892189L;
 
     /**
@@ -177,15 +178,16 @@ public class ArrayList<E> extends Abstra
      * @throws NullPointerException if the specified collection is null
      */
     public ArrayList(Collection<? extends E> c) {
-        elementData = c.toArray();
-        if ((size = elementData.length) != 0) {
-            // defend against c.toArray (incorrectly) not returning Object[]
-            // (see e.g. https://bugs.openjdk.java.net/browse/JDK-6260652)
-            if (elementData.getClass() != Object[].class)
-                elementData = Arrays.copyOf(elementData, size, Object[].class);
+        Object[] a = c.toArray();
+        if ((size = a.length) != 0) {
+            if (c.getClass() == ArrayList.class) {
+                elementData = a;
+            } else {
+                elementData = Arrays.copyOf(a, size, Object[].class);
+            }
         } else {
             // replace with empty array.
-            this.elementData = EMPTY_ELEMENTDATA;
+            elementData = EMPTY_ELEMENTDATA;
         }
     }
 
@@ -855,6 +857,7 @@ public class ArrayList<E> extends Abstra
      *             instance is emitted (int), followed by all of its elements
      *             (each an {@code Object}) in the proper order.
      */
+    // OPENJDK @java.io.Serial
     private void writeObject(java.io.ObjectOutputStream s)
         throws java.io.IOException {
         // Write out element count, and any hidden stuff
@@ -882,6 +885,7 @@ public class ArrayList<E> extends Abstra
      *         could not be found
      * @throws java.io.IOException if an I/O error occurs
      */
+    // OPENJDK @java.io.Serial
     private void readObject(java.io.ObjectInputStream s)
         throws java.io.IOException, ClassNotFoundException {
 
@@ -1136,7 +1140,7 @@ public class ArrayList<E> extends Abstra
             this.parent = parent;
             this.offset = parent.offset + fromIndex;
             this.size = toIndex - fromIndex;
-            this.modCount = root.modCount;
+            this.modCount = parent.modCount;
         }
 
         public E set(int index, E element) {
@@ -1289,7 +1293,7 @@ public class ArrayList<E> extends Abstra
             return new ListIterator<E>() {
                 int cursor = index;
                 int lastRet = -1;
-                int expectedModCount = root.modCount;
+                int expectedModCount = SubList.this.modCount;
 
                 public boolean hasNext() {
                     return cursor != SubList.this.size;
@@ -1333,7 +1337,7 @@ public class ArrayList<E> extends Abstra
                         final Object[] es = root.elementData;
                         if (offset + i >= es.length)
                             throw new ConcurrentModificationException();
-                        for (; i < size && modCount == expectedModCount; i++)
+                        for (; i < size && root.modCount == expectedModCount; i++)
                             action.accept(elementAt(es, offset + i));
                         // update once at end to reduce heap write traffic
                         cursor = i;
@@ -1359,7 +1363,7 @@ public class ArrayList<E> extends Abstra
                         SubList.this.remove(lastRet);
                         cursor = lastRet;
                         lastRet = -1;
-                        expectedModCount = root.modCount;
+                        expectedModCount = SubList.this.modCount;
                     } catch (IndexOutOfBoundsException ex) {
                         throw new ConcurrentModificationException();
                     }
@@ -1385,7 +1389,7 @@ public class ArrayList<E> extends Abstra
                         SubList.this.add(i, e);
                         cursor = i + 1;
                         lastRet = -1;
-                        expectedModCount = root.modCount;
+                        expectedModCount = SubList.this.modCount;
                     } catch (IndexOutOfBoundsException ex) {
                         throw new ConcurrentModificationException();
                     }