removeLast
public E removeLast() {return remove(header.previous);}删除链表中最后一个元素，并返回其值
addFirst
public void addFirst(E e) {addBefore(e, header.next);}在链表头部插入一个元素
addLast
public void addLast(E e) {addBefore(e, header);}在链表添加尾部插入一个元素
contains
public boolean contains(Object o) {return indexOf(o) != -1;}检查是否包含指定元素
size
public int size() {return size;}返回链表中元素的个数
add
public boolean add(E e) {addBefore(e, header);return true;}在链表尾部加入一个元素
public void add(int index, E element) {addBefore(element, (index == size ? header : entry(index)));}在某个位置加入元素
remove
public boolean remove(Object o) {if (o == null) {for (Entry<E> e = header.next; e != header; e = e.next) {if (e.element == null) {remove(e);return true;}}} else {for (Entry<E> e = header.next; e != header; e = e.next) {if (o.equals(e.element)) {remove(e);return true;}}}return false;}删除某个元素，首先判断元素是否为null，然后进行相关的查找。
public E remove(int index) {return remove(entry(index));}删除某一位置的元素
addAll
public boolean addAll(Collection<? extends E> c) {return addAll(size, c);}将集合添加到链表的尾部
public boolean addAll(int index, Collection<? extends E> c) {if (index < 0 || index > size) //边界范围校验throw new IndexOutOfBoundsException("Index: " + index + ", Size: "+ size);Object[] a = c.toArray(); //将集合转化成数组int numNew = a.length; //数组的长度if (numNew == 0)return false; //空集合则不用添加modCount++; //结构变动变量自增Entry<E> successor = (index == size ? header : entry(index)); //确定集合元素添加到哪个元素之前，记为EEntry<E> predecessor = successor.previous; //保存E的前一个元素for (int i = 0; i < numNew; i++) { //循环要加入到链表的集合，Entry<E> e = new Entry<E>((E) a[i], successor, predecessor); //构建元素并将其next和previous分别指向E、E.previous。predecessor.next = e; //将E.previous的next指向新节点，这样新节点就会插入到链表中。仔细考虑此处并没有立即将successor的previous指向新节点，而是在整个循环结束之后才处理。predecessor = e; //将新构建的元素赋值给predecessor，即E.previous为新插入的节点，如此反复最终将这些集合元素添加到链表中}successor.previous = predecessor; //修复E的previous指向size += numNew; //链表大小调整return true;}将集合中的元素添加到链表指定位置，方法具体解释见代码后的注释。
clear
public void clear() {Entry<E> e = header.next;while (e != header) {Entry<E> next = e.next;e.next = e.previous = null;e.element = null;e = next;}header.next = header.previous = header;size = 0;modCount++;}清空链表
get
public E get(int index) {return entry(index).element;}返回某个位置的值
set
public E set(int index, E element) {Entry<E> e = entry(index);E oldVal = e.element;e.element = element;return oldVal;}设置某个位置的值
indexOf
public int indexOf(Object o) {int index = 0;if (o == null) {for (Entry e = header.next; e != header; e = e.next) {if (e.element == null)return index;index++;}} else {for (Entry e = header.next; e != header; e = e.next) {if (o.equals(e.element))return index;index++;}}return -1;}返回某个元素在链表中首次出现的位置，未找到则返回-1
lastIndexOf
public int lastIndexOf(Object o) {int index = size;if (o == null) {for (Entry e = header.previous; e != header; e = e.previous) {index--;if (e.element == null)return index;}} else {for (Entry e = header.previous; e != header; e = e.previous) {index--;if (o.equals(e.element))return index;}}return -1;}返回某个元素在链表中最后出现的位置，未找到则返回-1
peek
public E peek() {if (size == 0)return null;return getFirst();}返回链表中的第一元素
element
public E element() {return getFirst();}返回链表中的第一个元素，该方法同上面的peek方法的区别在于当链表为空时，peek返回为null，而element方法抛出NoSuchElementException异常
poll
public E poll() {if (size == 0)return null;return removeFirst();}返回链表中的第一个元素，并将其在链表中移除，当链表为空时返回null
remove
public E remove() {return removeFirst();}返回链表中的第一个元素，并将其从链表中移除，当链表为空时抛出NoSuchElementException异常
offer
public boolean offer(E e) {return add(e);}在链表的尾部加入元素
offerFirst
public boolean offerFirst(E e) {addFirst(e);return true;}在链表的头部加入元素
offerLast
public boolean offerLast(E e) {addLast(e);return true;}在链表的尾部加入元素
peekFirst
public E peekFirst() {if (size == 0)return null;return getFirst();}返回链表第一个元素，当链表为空时返回null
peekLast
public E peekLast() {if (size == 0)return null;return getLast();}返回链表的最后一个元素，当链表为空时返回null
entry
private Entry<E> entry(int index) {if (index < 0 || index >= size)throw new IndexOutOfBoundsException("Index: " + index + ", Size: "+ size);Entry<E> e = header;if (index < (size >> 1)) {for (int i = 0; i <= index; i++)e = e.next;} else {for (int i = size; i > index; i--)e = e.previous;}return e;}该方法为私有方法，返回某个位置的元素
