public SearchResult searchKey(int key)
    {
        //节点不存在任何key
        if (size == 0)
        {
            return null;
        }
        int index = 0;
        for (index = 0; index < size; index++)
        {
            int value = keyList[index];
            if (value >= key)
            {
                break;
            }
        }
        int current = keyList[index];
        if (current == key)
        {
            return new SearchResult(this, index);
        }
        
        //叶节点没有子树，没有找到
        if (isLeaf)
        {
            return null;
        }
        
        return subTreeNodeList[index].searchKey(key);
    }