public void appendToTail(){
  lock.lock();
  try {
    next=sentinel;
    final Node<K,V> tail=sentinel.prev;
    sentinel.prev=this;
    tail.next=this;
    prev=tail;
  }
  finally {
    lock.unlock();
  }
}

public void appendToTail ( ) { lock . lock ( ) ; try { next = sentinel ; final Node < K , V > tail = sentinel . prev ; sentinel . prev = this ; tail . next = this ; prev = tail ; } finally { lock . unlock ( ) ; } }
appends the node to the tail of the list .
