static class Entry<K,V> implements Map.Entry<K,V> {
　　　final K key;//key
        V value;//value
        Entry<K,V> next;//链表结构，指定的下一个Entry
        int hash;//通过散列获取的唯一的hash值，在put环节将作为一部分条件来验证Entry是否重复

        /**
         * Creates new entry.
         */
        Entry(int h, K k, V v, Entry<K,V> n) {
            value = v;
            next = n;
            key = k;
            hash = h;
        }

        public final K getKey() {
            return key;
        }

        public final V getValue() {
            return value;
        }

        public final V setValue(V newValue) {
            V oldValue = value;
            value = newValue;
            return oldValue;
        }

        public final boolean equals(Object o) {
            if (!(o instanceof Map.Entry))
                return false;
            Map.Entry e = (Map.Entry)o;
            Object k1 = getKey();
            Object k2 = e.getKey();
            if (k1 == k2 || (k1 != null && k1.equals(k2))) {
                Object v1 = getValue();
                Object v2 = e.getValue();
                if (v1 == v2 || (v1 != null && v1.equals(v2)))
                    return true;
            }
            return false;
        }

        public final int hashCode() {
            return Objects.hashCode(getKey()) ^ Objects.hashCode(getValue());
        }

        public final String toString() {
            return getKey() + "=" + getValue();
        }

        /**
         * This method is invoked whenever the value in an entry is
         * overwritten by an invocation of put(k,v) for a key k that‘s already
         * in the HashMap.
         */
        void recordAccess(HashMap<K,V> m) {
        }

        /**
         * This method is invoked whenever the entry is
         * removed from the table.
         */
        void recordRemoval(HashMap<K,V> m) {
        }
    }

public V put(K key, V value) {
        //是否需要初始化，区别在于put是否是第一次操作，如果是第一次操作将会初始化一个数组table出来
        if (table == EMPTY_TABLE) {
            inflateTable(threshold);
        }
        //HashMap是可以put key为null的键值对的，此Entry将会放在table[0]所在的链表下，具体在链表的什么位置只能看他是什么时候put进去的了，毕竟链表结构是先来得先排前面
        if (key == null)
            return putForNullKey(value);
        //通过散列获取hash
        int hash = hash(key);
        //通过hash和table长度确定所属链表 下标（分组）
        int i = indexFor(hash, table.length);
        for (Entry<K,V> e = table[i]; e != null; e = e.next) {
            Object k;
            //关于HashMap put如何确定put的key重复 在此处做了逻辑判断
            if (e.hash == hash && ((k = e.key) == key || key.equals(k))) {
                V oldValue = e.value;
                e.value = value;
                e.recordAccess(this);
                return oldValue;
            }
        }

        modCount++;
        //后续会有扩容操作
        addEntry(hash, key, value, i);
        return null;
    }        

 /**
     * Returns index for hash code h.
     */
    static int indexFor(int h, int length) {
        // assert Integer.bitCount(length) == 1 : "length must be a non-zero power of 2";
        //通过与运算 返回了一个 0至length-1之间的int数据
        return h & (length-1);
    }