Hashmap非线程安全关于hash值冲突处理

final V putVal(int hash, K key, V value, boolean onlyIfAbsent,
                   boolean evict) {
        node<K,V>[] tab; Node<K,V> p; int n, i;
        if ((tab = table) == null || (n = tab.length) == 0)//没有初始化，则要初始化，初始化调用的也是resize（）方法
            n = (tab = resize()).length; 
        if ((p = tab[i = (n - 1) & hash]) == null)
            tab[i] = newNode(hash, key, value, null);//这个位置没有值，直接插入，重写hash方法的作用体现在这里
        else {//出现了冲突
            Node<K,V> e; K k;
            if (p.hash == hash &&
                ((k = p.key) == key || (key != null && key.equals(k))))//找到了如该key equal的value
                e = p;
            else if (p instanceof TreeNode)//事树节点，插入到树里。jdk8冲突节点数目达到一定值后，使用树结构存储
                e = ((TreeNode<K,V>)p).putTreeVal(this, tab, hash, key, value);
            else {
                for (int binCount = 0; ; ++binCount) {//一直找到链表的结尾，将k-v插入
                    if ((e = p.next) == null) {
                        p.next = newNode(hash, key, value, null);
                        if (binCount >= TREEIFY_THRESHOLD - 1) // -1 for 1st
                            treeifyBin(tab, hash);//是否需要改成树存储
                        break;
                    }
                    if (e.hash == hash &&
                        ((k = e.key) == key || (key != null && key.equals(k))))
                        break;
                    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;
    }