双向链表中有 val 域，next 域 ，prev 域。next 指向下一个节点，prev指向前一个节点

双向链表的模拟实现

import linkedlistdemo.MySingleList;

import java.util.List;

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

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

    //打印链表
    public void show() {
        ListNode cur = head;
        while(cur != null) {
            System.out.print(cur.val +" ");
            cur = cur.next;
        }
        System.out.println();
    }
    //查找是否包含key
    public boolean contains(int key) {
        ListNode cur = head;
        while(cur != null) {
            if(cur.val == key) {
                return true;
            }
            cur = cur.next;
        }
        return false;
    }
    //计算链表长度size
    public int size() {
        ListNode cur = head;
        int count = 0;
        while(cur != null) {
            count++;
            cur = cur.next;
        }
        return count;
    }
    //头插法
    public void addFirst(int data) {
        ListNode node = new ListNode(data);
        if(head == null) {
            head = node;
            last = node;
        }else {
            node.next = head;
            head.prev = node;
            head = node;
        }
    }
    //尾插法
    public void addLast(int data) {
        ListNode node = new ListNode(data);
        if(head == null) {
            head = node;
            last = node;
        }else {
            last.next = node;
            node.prev = last;
            last = node;
        }
    }
    //任意位置插入，第一个结点为0号下标
    public void addIndex(int index,int data)  {
        if(index < 0 || index > size()) {
            return;
        }
        if(index == 0) {
            addFirst(data);
        }
        if (index == size()) {
            addLast(data);
        }
        ListNode node = new ListNode(data);
        ListNode cur = searchNode(index);
        node.next = cur;
        cur.prev.next = node;
        node.prev = cur.prev;
        cur.prev = node;
    }
    private ListNode searchNode(int index) {
        ListNode cur = head;
        int count = 0;
        while(count != index) {
            cur = cur.next;
            count++;
        }
        return cur;
    }
    //删除val值为key的结点
    public void remove(int key) {
        if(head == null) return;
        ListNode cur = head;
        while(cur != null) {
            if(cur.val == key) {
                if(cur == head) {
                    if(cur.next == null) {
                        cur = null;
                    }else {
                        head = head.next;
                        head.prev = null;
                    }
                    return;
                }
                if(cur == last) {
                    cur.prev.next = null;
                    last = cur.prev;
                    return;
                }
                cur.prev.next = cur.next;
                cur.next.prev = cur.prev;
                return;
            }
            cur = cur.next;
        }
    }
    //删除所有值为key的结点
    public void removeAll(int key) {
        ListNode cur = head;
        while(cur != null) {
            if(cur.val == key) {
                if(cur == head) {
                    if(cur.next == null) {
                        cur = null;
                        return;
                    }else {
                        cur.next.prev = null;
                        head = head.next;
                    }
                }else if(cur == last) {
                    cur.prev.next = null;
                    last = cur.prev;
                }else {
                    cur.prev.next = cur.next;
                    cur.next.prev = cur.prev;
                }
            }
            cur = cur.next;
        }
    }
    //清除链表
    public void clear() {
        ListNode cur = head;
        ListNode curN = null;
        while(cur != null) {
            curN = cur.next;
            cur.next = null;
            cur.prev = null;
            cur = curN;
        }
        head = null;
        last = null;
    }
}

带头单向非循环链表的模拟实现

public class MySingleList {
    //创建节点类
    static class Node {
        public int val;
        public Node next;
        public Node(int val) {
            this.val = val;
            this.next = null;
        }
        public Node () {

        }
    }
    //创建链表类,包含关于操作链表的方法
    public static class LinkedList {
        private Node head;//头结点
        public LinkedList() {
            head = null;//带头空链表
        }

        //头插
        public void addFirst(int val) {
            Node newNode = new Node(val);
            newNode.next = head;
            head = newNode;
        }

        //尾插
        public void addLast(int val) {
            Node newNode = new Node(val);
            if(head == null) {
                head = newNode;
                return;
            }
            Node cur = head;
            while (cur.next != null) {
                cur = cur.next;
            }
            cur.next = newNode;
        }


        //获取链表的长度
        public int size() {
            int count = 0;
            Node cur = head;
            while (cur != null) {
                count++;
                cur = cur.next;
            }
            return count;
        }

        //打印链表
        public void print() {
            Node cur = head;
            while (cur != null) {
                System.out.print(cur.val + " ");
                cur = cur.next;
            }
        }


        //在第pos个位置插入节点
        public void addIndex(int pos, int val) {
            if (pos <= 0 || pos > size()+1) {
                throw new PosOutOfException("下标位置不合法");
            }
            if (pos == 1) {
                addFirst(val);
            }else if(pos == size()+1){
                addLast(val);
            }else {
                //在第pos个位置插入，cur需要走pos-2次，此时cur指向目标位置的前驱
                Node cur = head;
                for (int i = 0; i < pos - 2; i++) {
                    cur = cur.next;
                }
                Node newNode = new Node(val);
                newNode.next = cur.next;
                cur.next = newNode;
            }
        }

        //删除第pos个位置的结点
        public void remove(int pos) {
            if (pos <= 0 || pos > size() + 1) {
                throw new PosOutOfException("下标位置不合法");
            }
            if(pos == 1) {
                head = head.next;
                return;
            }
            //cur走pos-2后，cur指向目标位置的前驱
            Node cur = head;
            for (int i = 0; i < pos-2; i++) {
                cur = cur.next;
            }
            cur.next = cur.next.next;
        }

        //删除值为key的节点
        public void removeVal(int key) {
            if(head == null) {
                return;
            }
            if(head.val == key) {
                head = head.next;
                return;
            }
            Node ret = findLastNode(key);
            if(ret == null) {
                return;
            }
            ret.next = ret.next.next;
        }

        //找到值为key的前一个节点
        public Node findLastNode(int key) {
            if(head == null) return null;
            Node cur = head.next;
            Node pre = head;
            while(cur != null) {
                if(cur.val == key) {
                    return pre;
                }
                pre = cur;
                cur = cur.next;
            }
            return null;
        }


        //查找是否包含节点值为key的节点
        public boolean contains(int key) {
            if(head == null) {
                return false;
            }
            Node cur = head;
            while (cur != null) {
                if (cur.val == key) {
                    return true;
                }
                cur = cur.next;
            }
            return false;
        }
    }
}

ArrayList 和 LinkedList 的区别