public void test() {
        LinkedList<Integer> list = new LinkedList<>();
        for (int i = 0; i < 100000; i++) {//插入100000條數(shù)據(jù)
            list.add(i);
        }
        int index = 0;//記錄最后一個元素
        long time1 = System.currentTimeMillis();
        for (int i = 0; i < list.size(); i++) {//普通for循環(huán)遍歷
            index = list.get(i);
        }
        long time2 = System.currentTimeMillis();
        LogUtil.Companion.d("1:" + (time2 - time1) + " index->" + index);
        for (int i : list) {//增強for循環(huán)遍歷
            index = i;
        }
        long time3 = System.currentTimeMillis();
        LogUtil.Companion.d("2:" + (time3 - time2) + " index->" + index);
        Iterator<Integer> iterator = list.listIterator();
        while (iterator.hasNext()) {//iterator遍歷
            index = iterator.next();
        }
        long time4 = System.currentTimeMillis();
        LogUtil.Companion.d("3:" + (time4 - time3) + " index->" + index);
    }

//LinkedList.java
    public E get(int index) {
        checkElementIndex(index); //只是檢測是否數(shù)組越界
        return node(index).item; //調(diào)用了node(index)方法
    /**
     * Returns the (non-null) Node at the specified element index.
     */
    Node<E> node(int index) {
        // assert isElementIndex(index);
//判斷index離頭部近一點還是離尾部近一點
        if (index < (size >> 1)) {
            Node<E> x = first;
            for (int i = 0; i < index; i++)
                x = x.next;
            return x;
        } else {
            Node<E> x = last;
            for (int i = size - 1; i > index; i--)
                x = x.prev;
            return x;
        }
     }
    }

//LinkedList.java
public ListIterator<E> listIterator(int index) {
        checkPositionIndex(index);
        return new ListItr(index);
    }
    private class ListItr implements ListIterator<E> {
        private Node<E> lastReturned;
        private Node<E> next;
        private int nextIndex;
        private int expectedModCount = modCount;
        ListItr(int index) {
            // assert isPositionIndex(index);
            next = (index == size) ? null : node(index);
            nextIndex = index;
        }
        public boolean hasNext() {
            return nextIndex < size;
        }
        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();
        }
    }