六种方法的实现：
package list; import java.util.ArrayList; import java.util.List; /** *@author Edward *@date 2020年6月30日---下午2:32:40 */ public class LinkedList<E> { private Node head; private int size; class Node{ E data; Node prev; Node next; Node(E e) { data=e; } } public boolean add(E e) { Node node = new Node(e); if (head==null) { head = node; head.next = head; head.prev = head; size++; return true; } Node last = head.prev; last.next = node; node.prev = last; head.prev = node; node.next = head; size++; return true; } public void add(int index,E e) { if (index<0||index>size) { throw new IndexOutOfBoundsException("下标越界啦"); } Node node = new Node(e); if (head==null) { head=node; // 当head是唯一节点时，必须设置前后为自己(其默认值均为null)，否则toString遍历中会空指针 head.next = head; head.prev = head; size++; return; } Node next = getNode(index); Node prev = next.prev; node.next = next; next.prev = node; prev.next = node; node.prev = prev; if (index == 0) { head = node; } size++; } public String toString() { if (head==null) { return "[]"; } Node dummyHead = new Node(null); dummyHead.next = head; List<E>list = new ArrayList<E>(); do { dummyHead = dummyHead.next; list.add(dummyHead.data); } while (dummyHead.next!=head); return list.toString(); } public int size() { return size; } public E get(int index) { if (index<0||index>=size) { throw new IndexOutOfBoundsException("下标越界啦"); } Node node = getNode(index); return node.data; } public E remove(int index) { if (index<0||index>=size) { throw new IndexOutOfBoundsException("下标越界啦"); } // 这个双向循环链表的很多操作是基于头节点的，因此可能影响head的操作需要特殊处理 // 边界条件，如果整个链表只有一个节点，需设置头节点为null if (size==1) { E data = head.data; head = null; size--; return data; } Node node = getNode(index); node.prev.next = node.next; node.next.prev = node.prev; size--; // 边界条件，如果删除的是头节点，需重新设置一个头节点 if (index==0) { head=node.next; } return node.data; } private Node getNode(int index) { Node node = head; if (index<size/2) { for (int i = 0; i < index; i++) { node = node.next; } }else { for (int i = size; i > index; i--) { node= node.prev; } } return node; } }