public class DuLinkList<T> {// 定义一个内部类Node，Node实例代表链表的节点private class Node {// 保存节点的数据private T data;// 指向上个节点的引用private Node prev;// 指向下个节点的引用private Node next;public Node() {}public Node(T data, Node prev, Node next) {this.data = data;this.prev = prev;this.next = next;}}// 保存该链表的头节点private Node header;// 保存该链表的尾节点private Node tail;// 保存该链表中已包含的节点数private int size;// 创建空链表public DuLinkList() {header = null;tail   = null;}// 以指定数据元素来创建链表，该链表只有一个元素public DuLinkList(T element) {header = new Node(element, null, null);// 只有一个节点,header和tail都是nulltail = header;size++;}// 返回链表的长度public int length() {return size;}// 获取链式线性表中索引为index处的元素public T get(int index) {return getNodeByIndex(index).data;}// 根据索引index获取指定位置的节点private Node getNodeByIndex(int index) {if (index < 0 || index > size - 1) {throw new IndexOutOfBoundsException("线性表索引越界");}if (index <= size / 2) {// 从header节点开始Node current = header;for (int i = 0; i <= size / 2 && current != null; i++, current = current.next) {if (i == index) {return current;}}} else {// 从tail节点开始搜索Node current = tail;for (int i = size - 1; i > size / 2 && current != null; i--, current= current.prev) {if (i == index) {return current;}}}return null;}// 查找链式线性表中指定元素的索引public int locate(T element) {// 从头节点开始搜索Node current = header;for (int i = 0; i < size && current != null; i++, current = current.next) {if (current.data.equals(element)) {return i;}}return -1;}// 采用尾插法为链表添加新节点public void add(T element) {if (header == null) {header = new Node(element, null, null);// 只有一个节点，header、tail都指向该节点tail = header;} else {// 创建新节点，新节点的pre指向原tail节点Node newNode = new Node(element, tail, null);// 让尾节点的next指向新增的节点tail.next = newNode;// 以新节点作为新的尾节点tail = newNode;}size++;}// 采用头插法为链表添加新节点public void addAtHeader(T element) {// 创建新节点，让新节点的next指向原来的header，并以新节点作为新的headerheader = new Node(element, null, header);// 如果插入前是空链表if (tail == null) {tail = header;} else {header.prev = newNode;header = newNode;}size++;}// 向线性链式表的指定位置插入一个元素public void insert(T element, int index) {if (index < 0 || index > size) {throw new IndexOutOfBoundsException("线性表索引越界");}// 如果还是空链表if (header == null) {add(element);} else {// 当index为0时，也就是在链表头处插入if (index == 0) {addAtHeader(element);} else {// 获取插入点的前一个节点Node prev = getNodeByIndex(index - 1);// 获取插入点的节点Node next = prev.next;// 让新节点的next引用指向next节点，prev引用指向prev节点Node newNode = new Node(element, prev, next);// 让prev的next指向新节点prev.next = newNode;// 让prev的下一个节点的prev指向新节点next.prev = newNode;size++;}}}// 删除链式线性表中指定索引处的元素public T delete(int index) {if (index < 0 || index > size - 1) {throw new IndexOutOfBoundsException("线性表索引越界");}Node del = null;// 如果被删除的是header节点if (index == 0) {del = header;header = header.next;// 释放新的header节点的prev引用header.prev = null;del.next = null;} else {// 获取删除点的前一个节点Node prev = getNodeByIndex(index - 1);// 获取将要被删除的节点del = prev.next;// 让被删除节点前一个节点的next指向被删除节点的下一个节点prev.next = del.next;// 让被删除节点的下一个节点的prev指向prev节点if (del.next != null) {del.next.prev = prev;} else {tail = prev;}// 将被删除节点的prev、next引用赋为nulldel.prev = null;del.next = null;}size--;return del.data;}// 删除链式线性表中最后一个元素public T remove() {return delete(size - 1);}// 判断链式线性表是否为空链表public boolean empty() {return size == 0;}// 清空线性表public void clear() {// 将底层数据所有元素赋为nullheader = null;tail   = null;size   = 0;}public String toString() {// 链表为空链表时if (empty()) {return "[]";} else {StringBuilder sb = new StringBuilder("[");for (Node current = header; current != null; current = current.next) {sb.append(current.data.toString() + ", ");}int len = sb.length();return sb.delete(len - 2, len).append("]").toString();}}public String reverseToString() {// 链表为空链表时if (empty()) {return "[]";} else {StringBuilder sb = new StringBuilder("[");for (Node current = tail; current != null; current = current.prev) {sb.append(current.data.toString() + ", ");}int len = sb.length();return sb.delete(len - 2, len).append("]").toString();}}
}

public class DuLinkListTest {public static void main(String[] args) {DuLinkList<String> list = new DuLinkList<String>();list.insert("aaaa", 0);list.add("bbbb");list.insert("cccc",0);list.insert("dddd", 1);System.out.println("双向链式线性表增加元素后列表：" + list.toString());list.delete(2);System.out.println("双向链式线性表删除元素后列表：" + list.toString());System.out.println("双向链式线性表反置元素后列表：" + list.reverseToString());System.out.println("cccc在线性表中的位置：" + list.locate("cccc"));System.out.println("链表中索引1处的元素：" + list.get(1));list.remove();System.out.println("调用remove方法后的链表：" + list);list.delete(0);System.out.println("调用delete(0)后的链表：" + list);}
}