This is a SUNBUG for 100193: https://bugs.openjdk.java.net/show_bug.cgi?id=100193

AbstractList.java defines addAll as follows:

    public boolean addAll(int index, Collection<? extends E> c) {
        rangeCheckForAdd(index);
        boolean modified = false;
        for (E e : c) {
            add(index++, e);
            modified = true;
        }
        return modified;
    }

with unnecessary 'modified' var; by definition of foreach, only case in which
'modified == false' is when e.isEmpty; code should be replaced by shorted and
faster version, e.g.

    public boolean addAll(int index, Collection<? extends E> c) {
        rangeCheckForAdd(index);
        for (E e : c)
            add(index++, e);
        return !c.isEmpty();
    }

ArrayList uses following code in some places (example of fastRemove here, but
similar code is used in e.g. remove, addAll, removeRange etc.)

    private void fastRemove(int index) {
        modCount++;
        int numMoved = size - index - 1;
        if (numMoved > 0)
            System.arraycopy(elementData, index+1, elementData, index,
                             numMoved);
        elementData[--size] = null; // Let gc do its work
    }

it can possibly be optimized to (clearer code, one less var initialized, less
math done):

    private void fastRemove(int index) {
        modCount++;
        size--;
        if (size != index)
            System.arraycopy(elementData, index+1, elementData, index, size -
index);
        elementData[size] = null; // Let gc do its work
    }
or, similarily (in removeRange):

        int numMoved = size - toIndex;
        System.arraycopy(elementData, toIndex, elementData, fromIndex,
                         numMoved);
to just (numMoved is not used anywhere else)
        System.arraycopy(elementData, toIndex, elementData, fromIndex,
                         size - toIndex);

btw, please inform me if I posted it in a wrong place; I'm not used to Java's
bugzilla.