Java | JDK8下的ConcurrentHashMap#get

 public V get(Object key) {
        Node<K,V>[] tab; Node<K,V> e, p; int n, eh; K ek;
         //寻址
        int h = spread(key.hashCode());
        if ((tab = table) != null && (n = tab.length) > 0 &&
            (e = tabAt(tab, (n - 1) & h)) != null) {
            //当头节点的hash值与key的hash值相同时，判断key的内容知否相同
            if ((eh = e.hash) == h) {
                if ((ek = e.key) == key || (ek != null && key.equals(ek)))
                    return e.val;
            }
            //如果头节点的hash值eh<0 红黑树存储 直接寻找
            else if (eh < 0)
                return (p = e.find(h, key)) != null ? p.val : null;
            //链表查找
            while ((e = e.next) != null) {
                if (e.hash == h &&
                    ((ek = e.key) == key || (ek != null && key.equals(ek))))
                    return e.val;
            }
        }
        return null;
    }