1. //在节点删除后，维护链表，传入删除的节点
    2. void afterNodeRemoval(Node<K,V> e) { // unlink
    3.         //p指向待删除元素，b执行前驱，a执行后驱
    4.         LinkedHashMap.Entry<K,V> p =
    5.             (LinkedHashMap.Entry<K,V>)e, b = p.before, a = p.after;
    6.         //这里执行双向链表删除p节点操作，很不简单。
    7.         p.before = p.after = null;
    8.         if (b == null)
    9.             head = a;
    10.         else
    11.             b.after = a;
    12.         if (a == null)
    13.             tail = b;
    14.         else
    15.             a.before = b;
    16.     }
    1.   //在节点被访问后根据accessOrder判断是否需要调整链表顺序
    2. void afterNodeAccess(Node<K,V> e) { // move node to last
    3.         LinkedHashMap.Entry<K,V> last;
    4.         if (accessOrder && (last = tail) != e) {
    5.             LinkedHashMap.Entry<K,V> p =
    6.                 (LinkedHashMap.Entry<K,V>)e, b = p.before, a = p.after;
    7.             p.after = null;
    8.             //这里执行双向链表删除操作
    9.             if (b == null)
    10.                 head = a;
    11.             else
    12.                 b.after = a;
    13.             if (a != null)
    14.                 a.before = b;
    15.             else
    16.                 last = b;
    17.             //这里执行将p放到尾部
    18.             if (last == null)
    19.                 head = p;
    20.             else {
    21.                 p.before = last;
    22.                 last.after = p;
    23.             }
    24.             tail = p;
    25.             ++modCount;
    26.         }
    27.     }
    1.     void afterNodeInsertion(boolean evict) { // possibly remove eldest
    2.         LinkedHashMap.Entry<K,V> first;
    3.         //removeEldestEntry(first)默认返回false，所以afterNodeInsertion这个方法其实并不会执行
    4.         if (evict && (first = head) != null && removeEldestEntry(first)) {
    5.             K key = first.key;
    6.             removeNode(hash(key), key, null, false, true);
    7.         }
    8.     }
    10.     protected boolean removeEldestEntry(Map.Entry<K,V> eldest) {
    11.         return false;
    12.     }

    此方法可用来实现LRU,重写removeEldestEntry方法，