[Java] Java源码解析LinkedList

private static class node<e> {
  e item;
  node<e> next;
  node<e> prev;
  node(node<e> prev, e element, node<e> next) {
  this.item = element;
  this.next = next;
  this.prev = prev;
  }
}

transient int size = 0;
/**
 * pointer to first node.
 * invariant: (first == null && last == null) ||
 *    (first.prev == null && first.item != null)
 **/
transient node<e> first;
/**
 * pointer to last node.
 * invariant: (first == null && last == null) ||
 *    (last.next == null && last.item != null)
 **/
transient node<e> last;

/**
 * returns the element at the specified position in this list.
 * @param index index of the element to return
 * @return the element at the specified position in this list
 * @throws indexoutofboundsexception {@inheritdoc}
 **/
public e get(int index) {
  checkelementindex(index);
  return node(index).item;
}
/**
 * returns the (non-null) node at the specified element index.
 **/
node<e> node(int index) {
  // assert iselementindex(index);
  if (index < (size >> 1)) {
  node<e> x = first;
  for (int i = 0; i < index; i++)
    x = x.next;
  return x;
  } else {
  node<e> x = last;
  for (int i = size - 1; i > index; i--)
    x = x.prev;
  return x;
  }
}

/**
 * appends the specified element to the end of this list.
 * <p>this method is equivalent to {@link #addlast}.
 * @param e element to be appended to this list
 * @return {@code true} (as specified by {@link collection#add})
 **/
public boolean add(e e) {
  linklast(e);
  return true;
}
/**
 * links e as last element.
 **/
void linklast(e e) {
  final node<e> l = last;
  final node<e> newnode = new node<>(l, e, null);
  last = newnode;
  if (l == null)
  first = newnode;
  else
  l.next = newnode;
  size++;
  modcount++;
}