java1.8 hashmap put方法 流程

   final V putVal(int hash, K key, V value, boolean onlyIfAbsent, boolean evict) {
        Node<K,V>[] tab; 
        Node<K,V> p; 
        int n, i;
        //判断当前hashmap里面是不是空，是resize下hashmap
        if ((tab = table) == null || (n = tab.length) == 0)
            n = (tab = resize()).length;
        //数据tab[i]复制给p 如果p是空的 直接new一个Node
        //这里不理解，tab是数组 数组下表取值恒小于tab.length 已经理解
        if ((p = tab[i = (n - 1) & hash]) == null)
            tab[i] = newNode(hash, key, value, null);
        else {
            Node<K,V> e; 
            K k;
            if (p.hash == hash &&
                ((k = p.key) == key || (key != null && key.equals(k))))
                e = p;
            //hash碰撞了，p如果是红黑树 使用红黑树的put方法
            else if (p instanceof TreeNode)
                e = ((TreeNode<K,V>)p).putTreeVal(this, tab, hash, key, value);
            //暂时还没有转化为红黑树
            else {
                for (int binCount = 0; ; ++binCount) {
                    //如果当前节点的next节点是空
                    if ((e = p.next) == null) {
                        //复制给p的next节点
                        p.next = newNode(hash, key, value, null);
                        if (binCount >= TREEIFY_THRESHOLD - 1) // -1 for 1st
                            treeifyBin(tab, hash);
                        break;
                    }
                    if (e.hash == hash &&
                        ((k = e.key) == key || (key != null && key.equals(k))))
                        break;
                    //此处是p的next节点不是空，就把p.next重新复制给p，e再去复制p。next。next 这样一直轮训到一个TREEIFY_THRESHOLD-1节点 就尝试红黑树了
                    p = e;
                }
            }
            if (e != null) { // existing mapping for key
                V oldValue = e.value;
                if (!onlyIfAbsent || oldValue == null)
                    e.value = value;
                afterNodeAccess(e);
                return oldValue;
            }
        }
        ++modCount;
        if (++size > threshold)
            resize();
        afterNodeInsertion(evict);
        return null;
    }