循环链表：

循环链表是另一种形式的链式存储结构。它的特点是表中最后一个结点的指针域指向头结点，整个链表形成一个环。

单循环链表的实现—链表增删改查功能

代码实现：

public class MyCircleLinkedList {
    private Node head;//头结点, 不存数据
    private Node tail;//尾结点, 指向链表的最后一个节点
    private int size;

    public MyCircleLinkedList() {
        head = new Node(Integer.MIN_VALUE, null);
        head.next = head;
        tail = head;
        size = 0;
    }

    /**
     * 添加到链表尾部
     *
     * @param item
     */
    public void add(int item) {
        /********** Begin *********/
        Node newNode = new Node(item,null);
        Node temp = head;
        for (int i = 0;i < size;i++){
            temp = temp.next;
        }
        temp.next = newNode;
        newNode.next = head.next;
        tail = newNode;
        size++;
        /********** End *********/
    }

    /**
     * 遍历链表并输出元素
     */
    public void output() {
        /********** Begin *********/
        if (isEmpty()){
            return;
        }
        Node temp = head.next;
        for (int i = 0;i < size;i++){
            System.out.println(temp.item);
            temp = temp.next;
        }
        /********** End *********/
    }
    
    /**
     * 删除从头结点开始的第index个结点
     * index从0开始
     *
     * @param index
     * @return
     */
    public int remove(int index) {
        checkPosIndex(index);

        /********** Begin *********/
        Node temp = head.next;
        for (int i = 0;i < size;i++){
            if (i == index - 1){
                break;
            }
            temp = temp.next;
        }
        Node reNode = temp.next;
        temp.next = temp.next.next;
        size--;
        return reNode.item;
        /********** End *********/
    }
    
    public boolean isEmpty() {
        return head.next == head;
    }

    public int size() {
        return size;
    }

    //结点内部类
    private static class Node {
        int item;
        Node next;

        Node(int item, Node next) {
            this.item = item;
            this.next = next;
        }
    }
}

双向循环链表的实现—链表增删改查功能

代码实现：

public class MyDoubleLinkedList {

    private Node head;//头结点
    private Node tail;//指向链表的尾结点
    private int size;

    public MyDoubleLinkedList() {
        head = new Node(null, Integer.MIN_VALUE, null);
        head.next = head.prev = head;
        tail = head;
        size = 0;
    }

    /**
     * 添加元素到表尾
     *
     * @param item
     */
    public void add(int item) {

        /********** Begin *********/
        Node newNode = new Node(null, item, null);
        tail.next = newNode;
        newNode.prev = tail;
        newNode.next = head;
        head.prev = newNode;
        tail = newNode;
        ++size;
        /********** End *********/

    }
    
	/**
     * 删除指定位置index出的结点，并返回其值
     *
     * @param index
     * @return
     */
    public int remove(int index) {
        checkPosIndex(index);//

        /********** Begin *********/
        Node temp = head.next;
        for (int i = 0;i < size;i++){
            if (i == index){
                break;
            }
            temp = temp.next;
        }
        temp.prev.next = temp.next;
        temp.next.prev = temp.prev;
        return temp.item;
        /********** End *********/
    }

    /**
     * 打印双向链表
     *
     * @param flag true从左向右顺序打印, false从右向左顺序打印
     */
    public void printList(boolean flag) {
        Node f = head;
        if (flag) {//向右
            while (f.next != head) {
                f = f.next;
                System.out.print(f.item + " ");
            }
        } else {//向左
            while (f.prev != head) {
                f = f.prev;
                System.out.print(f.item + " ");
            }
        }
    }

    public int size() {
        return size;
    }

    //结点内部类
    private static class Node {
        int item;
        Node next;//直接后继引用
        Node prev;//直接前驱引用

        Node(Node prev, int item, Node next) {
            this.prev = prev;
            this.item = item;
            this.next = next;
        }
    }
}