private class ListItr implements ListIterator<E> {
  private Node<E> lastReturned;
  private Node<E> next;
  private int nextIndex;
  private int expectedModCount = modCount;

public E next() {
  checkForComodification();
  if (!hasNext())
  throw new NoSuchElementException();

  lastReturned = next;
  next = next.next;
  nextIndex++;
  return lastReturned.item;
 }

 final void checkForComodification() {
  if (modCount != expectedModCount)
   throw new ConcurrentModificationException();
  

 // 添加元素到隊(duì)列最后
 public boolean add(E e) {
  // 修改modCount
  ensureCapacity(size + 1); // Increments modCount!!
  elementData[size++] = e;
  return true;
 }


 // 添加元素到指定的位置
 public void add(int index, E element) {
  if (index > size || index < 0)
   throw new IndexOutOfBoundsException(
   "Index: "+index+", Size: "+size);

  // 修改modCount
  ensureCapacity(size+1); // Increments modCount!!
  System.arraycopy(elementData, index, elementData, index + 1,
    size - index);
  elementData[index] = element;
  size++;
 }

 // 添加集合
 public boolean addAll(Collection<? extends E> c) {
  Object[] a = c.toArray();
  int numNew = a.length;
  // 修改modCount
  ensureCapacity(size + numNew); // Increments modCount
  System.arraycopy(a, 0, elementData, size, numNew);
  size += numNew;
  return numNew != 0;
 }


 // 刪除指定位置的元素
 public E remove(int index) {
  RangeCheck(index);

  // 修改modCount
  modCount++;
  E oldValue = (E) elementData[index];

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

  return oldValue;
 }


 // 快速刪除指定位置的元素
 private void fastRemove(int index) {

  // 修改modCount
  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
 }

 // 清空集合
 public void clear() {
  // 修改modCount
  modCount++;

  // Let gc do its work
  for (int i = 0; i < size; i++)
   elementData[i] = null;

  size = 0;
 }

public class CopyOnWriteArrayList<E>
 implements List<E>, RandomAccess, Cloneable, java.io.Serializable {

 ...

 // 返回集合對(duì)應(yīng)的迭代器
 public Iterator<E> iterator() {
  return new COWIterator<E>(getArray(), 0);
 }

 ...

 private static class COWIterator<E> implements ListIterator<E> {
  private final Object[] snapshot;

  private int cursor;

  private COWIterator(Object[] elements, int initialCursor) {
   cursor = initialCursor;
   // 新建COWIterator時(shí)，將集合中的元素保存到一個(gè)新的拷貝數(shù)組中。
   // 這樣，當(dāng)原始集合的數(shù)據(jù)改變，拷貝數(shù)據(jù)中的值也不會(huì)變化。
   snapshot = elements;
  }

  public boolean hasNext() {
   return cursor < snapshot.length;
  }