无头双向非循环链表大致与无头单向非循环差不多，只不过每个节点多了个prev引用，可以从后一个节点找到前一个节点。并且除了头节点head，双链表还多了个尾节点tail

要模拟实现无头双向非循环链表，同样需要创建三个文件：IList.java接口，MyLinkedList.java文件，test.java测试文件，下面仅展示IList.java接口和MyLinkedList.java文件

Ilist.java接口：

 // 2、无头双向链表实现
 public class LinkedList {
     //头插法
     public void addFirst(int data);
     //尾插法
     public void addLast(int data);
     //任意位置插入,第一个数据节点为0号下标
     public boolean addIndex(int index,int data);
     //查找是否包含关键字key是否在单链表当中
     public boolean contains(int key);
     //删除第一次出现关键字为key的节点
     public void remove(int key);
     //删除所有值为key的节点
     public void removeAllKey(int key);
     //得到单链表的长度
     public int size();
     public void display();
     public void clear();
 }

MyLinkedList.java：

public class MyLinkedList implements IList{
    static class ListNode {
        public int val;
        public ListNode next;
        public ListNode prev;

        public ListNode(int val) {
            this.val = val;
        }
    }
    public ListNode head;
    public ListNode tail;

    @Override
    public void addFirst(int data) {
        ListNode node = new ListNode(data);
        if(head == null) {
            head = tail = node;
            return;
        }
        node.next = head;
        head.prev = node;
        head = node;
    }

    @Override
    public void addLast(int data) {
        ListNode node = new ListNode(data);
        if(head == null) {
            head = tail = node;
            return;
        }
        node.prev = tail;
        tail.next = node;
        tail = node;
    }

    @Override
    public void addIndex(int index, int data) {
        int len = size();
        if(index < 0 || index > len) {
            return;
        }
        if(index == 0) {
            addFirst(data);
            return;
        }
        if(index == len) {
            addLast(data);
            return;
        }
        ListNode node = new ListNode(data);
        ListNode cur = findIndex(index);
        node.prev = cur;
        node.next = cur.next;
        cur.next.prev = node;
        cur.next = node;
    }

    private ListNode findIndex(int index) {
        ListNode cur = head;
        for(int i = 0; i < index-1; i++) {
            cur = cur.next;
        }
        return cur;
    }

    @Override
    public boolean contains(int key) {
        ListNode cur = head;
        while(cur != null) {
            if(cur.val == key) {
                return true;
            }
            cur = cur.next;
        }
        return false;
    }

    @Override
    public void remove(int key) {
        if(head == null) {
            return;
        }
        ListNode del = findKeyOfIndex(key);
        if(del == null) {
            return;
        }
        if(del.prev == null) {
            head = head.next;
            if(head != null) {
                head.prev = null;
            }
            return;
        }
        if(del.next == null) {
            tail = tail.prev;
            tail.next = null;
            return;
        }
        del.prev.next = del.next;
        del.next.prev = del.prev;
    }
    private ListNode findKeyOfIndex(int key) {
        ListNode cur = head;
        ListNode last = tail;
        while(cur != last) {
            if(cur.val == key) {
                return cur;
            }
            if(last.val == key) {
                return last;
            }
            cur = cur.next;
            last = last.prev;
        }
        if(cur.val == key) {
            return cur;
        }
        return null;
    }

    @Override
    public void removeAllKey(int key) {
        if(head == null) {
            return;
        }
        ListNode start = head;
        ListNode cur = head.next;
        while(cur != null) {
            if(cur.val == key) {
                start.next = cur.next;
                cur = cur.next;
                if(cur != null) {
                    cur.prev = start;
                }
            }else {
                start = cur;
                cur = cur.next;
            }
        }
        if(head.val == key) {
            head = head.next;
        }
    }

    @Override
    public int size() {
        int len = 0;
        ListNode cur = head;
        while(cur != null) {
            len++;
            cur = cur.next;
        }
        return len;
    }

    @Override
    public void clear() {
        ListNode cur = head;
        while(cur != null) {
            ListNode curN = cur.next;
            cur.prev = null;
            cur.next = null;
            cur = curN;
        }
        head = null;
        tail = null;
    }

    @Override
    public void display() {
        ListNode cur = head;
        while(cur != null) {
            System.out.print(cur.val+" ");
            cur = cur.next;
        }
        System.out.println();
    }
}