LinkedList源码疑问记录

      早上看linkedList源码时候，对于它的初始化一直不太明白。如下:

    

 transient int size = 0;

    /**
     * Pointer to first node.
     * Invariant: (first == null && last == null) ||
     *            (first.prev == null && first.item != null)
     */
    transient Node<E> first;

    /**
     * Pointer to last node.
     * Invariant: (first == null && last == null) ||
     *            (last.next == null && last.item != null)
     */
    transient Node<E> last;

  /**
     * Inserts all of the elements in the specified collection into this
     * list, starting at the specified position.  Shifts the element
     * currently at that position (if any) and any subsequent elements to
     * the right (increases their indices).  The new elements will appear
     * in the list in the order that they are returned by the
     * specified collection's iterator.
     *
     * @param index index at which to insert the first element
     *              from the specified collection
     * @param c collection containing elements to be added to this list
     * @return {@code true} if this list changed as a result of the call
     * @throws IndexOutOfBoundsException {@inheritDoc}
     * @throws NullPointerException if the specified collection is null
     */
    public boolean addAll(int index, Collection<? extends E> c) {
        checkPositionIndex(index);

        Object[] a = c.toArray();
        int numNew = a.length;
        if (numNew == 0)
            return false;

        Node<E> pred, succ;
        if (index == size) {
            succ = null;
            pred = last;
        } else {
            succ = node(index);
            pred = succ.prev;
        }

        for (Object o : a) {
            @SuppressWarnings("unchecked") E e = (E) o;
            Node<E> newNode = new Node<>(pred, e, null);
            if (pred == null)
                first = newNode;
            else
                pred.next = newNode;
            pred = newNode;
        }

        if (succ == null) {
            last = pred;
        } else {
            pred.next = succ;
            succ.prev = pred;
        }

        size += numNew;
        modCount++;
        return true;
    }

  一直不明白怎么赋值的。跟着代码调试后，刚开始是null，使用的时候每次add,然后再去赋值。大概过程如下：

另一个构造方法是带Collection值得对象作为入参的构造函数的，下面是执行逻辑：

1）使用this（）调用默认的无参构造函数。

2）调用addAll（）方法，传入当前的节点个数size，此时size为0，并将collection对象传递进去

3）检查index有没有数组越界的嫌疑

4）将collection转换成数组对象a

5）循环遍历a数组，然后将a数组里面的元素创建成拥有前后连接的节点，然后一个个按照顺序连起来。

6）修改当前的节点个数size的值

7）操作次数modCount自增1.

剩余的慢慢看~