无头双向链表模拟实现

public class MyLinkedList {
    //通过内部类来实现
    static class ListNode {
        private int val;
        private ListNode prev;
        private ListNode next;

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

        public int getVal() {
            return val;
        }

        public void setVal(int val) {
            this.val = val;
        }
    }
    public ListNode head;//双链表的头结点
    public ListNode last;//双链表的尾巴
    //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,第一个数据节点为0号下标
    public void addIndex(int index,int data){
        checkIndex(index);
        if(index==0){
            addFirst(data);
        }
        if (index==size()){
            addLast(data);
        }
        ListNode node=new ListNode(data);
        ListNode cur=searchIndex(index);
        node.next=cur;
        cur.prev.next=node;
        node.prev=cur.prev;
        cur.prev=node;


    }
    //检查数据的合法性
    public boolean checkIndex(int index){
        if(index<0||index>size()){
            throw new IndexOutOFException("index位置不合法！"+index);
        }
        return true;
    }
    //寻找index的位置
    private ListNode searchIndex(int index){
        ListNode cur=head;
        while (index!=0){
            cur=cur.next;
            index--;
        }
        return cur;
    }
    //查找是否包含关键字key是否在单链表当中
    public boolean contains(int key){
        ListNode cur=head;
        while (cur!=null){
            if(cur.val==key){
                return true;
            }
            cur=cur.next;
        }
        return false;
    }
    //删除第一次出现关键字为key的节点
    public void remove(int key){
        ListNode cur=head;
        while (cur!=null){
            if (cur.val==key){
                //删除头结点
                if (cur==head){
                    head=head.next;
                    if(head!=null){
                        //考虑只有一个节点的情况下
                        head.prev=null;
                    }else {
                        last=null;
                    }
                }else {
                    //删除中间节点和尾巴节点
                    if(cur.next!=null){
                        //删除中间节点
                        cur.prev.next=cur.next;
                        cur.next.prev=cur.prev;
                    }else {
                        //删除尾巴节点
                        cur.prev.next=cur.next;
                        last=last.prev;
                    }
                }
                return;
            }else {
                cur=cur.next;
            }
        }
    }
    //删除所有值为key的节点
    public void removeAllKey(int key){
        ListNode cur=head;
        while (cur!=null){
            if (cur.val==key){
                //删除头结点
                if (cur==head){
                    head=head.next;
                    if(head!=null){
                        //考虑只有一个节点的情况下
                        head.prev=null;
                    }else {
                        last=null;
                    }
                }else {
                    //删除中间节点和尾巴节点
                    if(cur.next!=null){
                        //删除中间节点
                        cur.prev.next=cur.next;
                        cur.next.prev=cur.prev;
                    }else {
                        //删除尾巴节点
                        cur.prev.next=cur.next;
                        last=last.prev;
                    }
                }
                cur=cur.next;
            }else {
                cur=cur.next;
            }
        }
    }
    //得到单链表的长度
    public int size(){
        ListNode cur=head;
        int len=0;
        while (cur!=null){
            len++;
            cur=cur.next;
        }
        return len;
    }
    public void display(){
        ListNode cur=head;

        while (cur!=null){
            System.out.print(cur.val+" ");
            cur=cur.next;
        }
    }
    public void clear(){
        ListNode cur=head;
        while (cur!=null){
            ListNode curNext=cur.next;
            cur.prev=null;
            cur.next=null;
            cur=curNext;
        }
        head=null;
        last=null;
    }
}

2.异常类

public class IndexOutOFException extends RuntimeException{
    public IndexOutOFException() {
    }

    public IndexOutOFException(String message) {
        super(message);
    }
}

3.测试类

public class Test {
    public static void main(String[] args) {
        MyLinkedList myLinkedList=new MyLinkedList();
        myLinkedList.addLast(1);
        myLinkedList.addLast(2);
        myLinkedList.addLast(3);
        myLinkedList.addLast(4);
        //System.out.println(myLinkedList.contains(2));
        //System.out.println(myLinkedList.size());
        //myLinkedList.addIndex(2,99);
        //myLinkedList.remove(2);
        //myLinkedList.removeAllKey(1);
        myLinkedList.clear();
        myLinkedList.display();
    }
}