public T removeAt(int index) {
    // Make sure the index provided is valid
    if (index < 0 || index >= size) {
      throw new IllegalArgumentException();
    }

    int i;
    Node<T> trav;

    // Search from the front of the list
    if (index < size / 2) {
      for (i = 0, trav = head; i != index; i++) {
        trav = trav.next;
      }
      // Search from the back of the list
    } else
      for (i = size - 1, trav = tail; i != index; i--) {
        trav = trav.prev;
      }

    return remove(trav);
  }

解释如何通过遍历来删除双链表。我不懂for循环