Java并发包之CopyOnWriteArrayList类的深入讲解

 /**
 * 将指定的元素追加到此列表的末尾
 *
 * @param e element to be appended to this list
 * @return {@code true} (as specified by {@link Collection#add})
 */
 public boolean add(E e) {
 // 声明可重入锁
 final ReentrantLock lock = this.lock;
 // 加锁
 lock.lock();
 try {
 // 获取当前数组
  Object[] elements = getArray();
  int len = elements.length;
 // 复制当前数组到一个新数组中
  Object[] newElements = Arrays.copyOf(elements, len + 1);
 // 添加元素
  newElements[len] = e;
 // 改变引用
  setArray(newElements);
  return true;
 } finally {
  lock.unlock();
 }
 }

 /**
 * 删除元素
 */
 public E remove(int index) {
 // 检查下标是否越界
 rangeCheck(index);
 // 记录修改次数
 modCount++;
 // 待删除的元素
 E oldValue = elementData(index);
 // 待删除元素下标之后的数组长度
 int numMoved = size - index - 1;
 if (numMoved > 0)
 // 删除元素
  System.arraycopy(elementData, index+1, elementData, index,
    numMoved);
 elementData[--size] = null; // clear to let GC do its work

 return oldValue;
 }

 /**
 * forEach 方法
 */
 @Override
 public void forEach(Consumer<? super E> action) {
 Objects.requireNonNull(action);
 // 记录modCount
 final int expectedModCount = modCount;
 @SuppressWarnings("unchecked")
 final E[] elementData = (E[]) this.elementData;
 final int size = this.size;
 // 遍历时判断modCount
 for (int i=0; modCount == expectedModCount && i < size; i++) {
  action.accept(elementData[i]);
 }
 // 不相同，抛出异常
 if (modCount != expectedModCount) {
  throw new ConcurrentModificationException();
 }
 }

 /**
 * 删除元素
 */
 public E remove(int index) {
 final ReentrantLock lock = this.lock;
 // 加锁
 lock.lock();
 try {
 // 获取当前数组
  Object[] elements = getArray();
 // 记录数组的长度
  int len = elements.length;
 // 记录待删除元素
  E oldValue = get(elements, index);
 // 记录待删除元素后一个元素到尾节点的长度
  int numMoved = len - index - 1;
 // 为0代表待删除元素就在数组的末尾
  if (numMoved == 0)
  setArray(Arrays.copyOf(elements, len - 1));
  else {
  Object[] newElements = new Object[len - 1];
 // 复制到新数组中
  System.arraycopy(elements, 0, newElements, 0, index);
  System.arraycopy(elements, index + 1, newElements, index,
     numMoved);
 // 改变引用
  setArray(newElements);
  }
  return oldValue;
 } finally {
  lock.unlock();
 }
 }

 /**
 * 遍历方法
 */
 public void forEach(Consumer<? super E> action) {
 if (action == null) throw new NullPointerException();
 // 获取当前数组
 Object[] elements = getArray();
 int len = elements.length;
 for (int i = 0; i < len; ++i) {
  @SuppressWarnings("unchecked") E e = (E) elements[i];
  action.accept(e);
 }
 }