JAVA深化篇_19—— 面试必问之LinkedList的源码分析

LinkedList的源码分析

添加元素

节点类

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;
   }
}

成员变量

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;

添加元素

/**
 * 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++;
}

头尾添加元素

addFirst

/**
 * Inserts the specified element at the beginning of this list.
 *
 * @param e the element to add
 */
public void addFirst(E e) {
  linkFirst(e);
}


/**
 * Links e as first element.
 */
private void linkFirst(E e) {
  final Node<E> f = first;
  final Node<E> newNode = new Node<>(null, e, f);
  first = newNode;
  if (f == null)
    last = newNode;
  else
    f.prev = newNode;
  size++;
  modCount++;
}

addLast

/**
 * Appends the specified element to the end of this list.
 *
 * <p>This method is equivalent to {@link #add}.
 *
 * @param e the element to add
 */
public void addLast(E e) {
  linkLast(e);
}


/**
 * 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++;
}

获取元素

/**
 * 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;
}

private void checkElementIndex(int index) {
  if (!isElementIndex(index))
    throw new IndexOutOfBoundsException(outOfBoundsMsg(index));
}

/**
 * Tells if the argument is the index of an existing element.
 */
private boolean isElementIndex(int index) {
  return index >= 0 && index < size;
}    

/**
 * 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;
   }
}