Java_HashMap的工作原理（Jdk1.8）

转载自：https://blog.csdn.net/qq_28051453/article/details/52622068

 

 

 

 

 

 

 public V put(K key, V value) {
        return putVal(hash(key), key, value, false, true);
    }
final V putVal(int hash, K key, V value, boolean onlyIfAbsent,
                   boolean evict) {
        Node<K,V>[] tab; Node<K,V> p; int n, i;
        //如果table数组为空或者长度为0，则进行扩容
       if ((tab = table) == null || (n = tab.length) == 0)
            n = (tab = resize()).length;
        //根据hash算法算出存储的下标，如果为空，即不发生碰撞，则直接存储
       if ((p = tab[i = (n - 1) & hash]) == null)
            tab[i] = newNode(hash, key, value, null);
        else {
            Node<K,V> e; K k;
            //如果发生碰撞，且键值对已经存在，则进行值得覆盖
           if (p.hash == hash &&
                ((k = p.key) == key || (key != null && key.equals(k))))
                e = p;
            //存储为树
           else if (p instanceof TreeNode)
                e = ((TreeNode<K,V>)p).putTreeVal(this, tab, hash, key, value);
            else {
                 //链表
                 for (int binCount = 0; ; ++binCount) {
                    if ((e = p.next) == null) {
                        p.next = newNode(hash, key, value, null);
                        //如果链上的结点大于</span><span style="font-size:14px;">REEEIFY_THRESHOLD(默认为8)，则转化为红黑树
                       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;
                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;
    }
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原文链接：https://blog.csdn.net/qq_28051453/article/details/52622068