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++;  }