双向循环链表

package com.datastructure.List;import java.util.Collection;import java.util.NoSuchElementException;/** * 当前类为双向循环链表 该链表各元素类型可以不相同，不可反序列化 *  * @author LEIQIAO *  * @param <E> */public class LinkedList<E> {private transient Entry<E> header = new Entry<E>(null, null, null);private transient int size = 0;public static void main(String[] args) {LinkedList<Integer> link = new LinkedList<Integer>();// 测试getFirst（）， removeFirst（）， addFirst（）；// System.out.println(link.getFirst());link.addFirst(1);link.addFirst(2);System.out.println(link.getFirst());link.listAll();}/** * Constructs an empty list. */public LinkedList() {header.next = header.previous = header;}/** * 放回当前链表的第一元素 *  * @return 链表的第一个元素 * @throws NoSuchElementException *             如果当前链表为空 */public E getFirst() {if (size == 0)throw new NoSuchElementException();return header.next.element;}/** * 返回当前链表的最后一个元素 *  * @return 最后一个元素 * @throws NoSuchElementException *             如果当前链表为空 */public E getLast() {if (size == 0)throw new NoSuchElementException();return header.previous.element;}/** * 移除同时返回当前链表的第一个元素 *  * @return 链表的第一个元素 * @throws NoSuchElementException *             链表为空 */public E removeFirst() {return remove(header.next);}/** * 移除且返回当前链表的最后一个元素 *  * @return the last element from this list * @throws NoSuchElementException *             if this list is empty */public E removeLast() {return remove(header.previous);}/** * 添加当前链表的首元素 *  * @param 元素的数据 */public void addFirst(E e) {addBefore(e, header.next);}/** * 添加最后一个元素 *  * @param 元素的数据 */public void addLast(E e) {addBefore(e, header);}/** * 返回链表的长度 *  * @return 链表元素的数量 */public int size() {return size;}/** * 移除该链表的第一个该元素 链表元素允许为空，空则允许删除 *  * @param 链表中需要移除的元素 * @return 如果该链表中包含元素则返回true */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;}/** * 从特定位置把该集合所有元素插入到链表中.  *  * @param index 讲集合中第一个元素插入链表的位置 * @param c 包含插入链表元素的集合 * @return 链表改变返回真 * @throws IndexOutOfBoundsException  *             {@inheritDoc} * @throws NullPointerException *             if the specified collection is null */public boolean addAll(int index, Collection<? extends E> c) {if (index < 0 || index > size)throw new IndexOutOfBoundsException("Index: " + index + ", Size: "+ size);Object[] a = c.toArray();int numNew = a.length;if (numNew == 0)return false;Entry<E> successor = (index == size ? header : entry(index));Entry<E> predecessor = successor.previous;for (int i = 0; i < numNew; i++) {Entry<E> e = new Entry<E>((E) a[i], successor, predecessor);predecessor.next = e;predecessor = e;}successor.previous = predecessor;size += numNew;return true;}/** * 返回索引位置的Entry<E> 索引位置从0开始，size表示元素的个数，即第size个为头结点 */private Entry<E> entry(int index) {if (index < 0 || index >= size)throw new IndexOutOfBoundsException("Index: " + index + ", Size: "+ size);Entry<E> e = header;// 双向循环链表：前半部分顺时针查找，后半部分逆时针查找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;}private E remove(Entry<E> e) {// 此处不可用size判断，因为头结点为算法的需要，规范操作，不可删除if (e == header)throw new NoSuchElementException();E result = e.element;e.previous.next = e.next;e.next.previous = e.previous;size--;return result;}private Entry<E> addBefore(E e, Entry<E> entry) {Entry<E> newEntry = new Entry<E>(e, entry, entry.previous);// newEntry.prrvious = entry.previousentry.previous.next = newEntry;// newEntry.next = entryentry.previous = newEntry;size++;return newEntry;}public void listAll() {for (Entry<E> p = header.next; p != header; p = p.next) {System.out.println(p.element);}}private static class Entry<E> {E element;Entry<E> next;Entry<E> previous;Entry(E element, Entry<E> next, Entry<E> previous) {this.element = element;this.next = next;this.previous = previous;}}}