public class MyList {

    static class Node {// 节点类

        Object data;

        Node next;

        public Node(Object data) {// 构造方法，为data赋值

            this.data = data;

            this.next = null;

        }

    }

    Node head;

    public MyList() {

        head = null;// 链表的构造方法

    }

    public void clear() {// 清除链表

        head = null;

    }

    public void bianli()// 遍历

    {

        Node p = head;

        while (p != null) {

            System.out.print(p.data + " ");

            p = p.next;

        }

        System.out.println();

    }

    public boolean isEmpty()// 推断是否为空

    {

        return head == null;

    }

    public int size() {// 节点个数

        Node p = head;

        int sum = 0;

        while (p != null) {

            sum++;

            p = p.next;

        }

        return sum;

    }

    // 在指定位置插入元素。下标从0開始

    public void insert(Object d, int pos) {

        if (pos < 0 || pos > size()) {

            throw new RuntimeException("下标错误");

        }

        Node newNode = new Node(d);

        if (pos == 0) {

            newNode.next = head;

            head = newNode;

        } else if (pos >= size() - 1) {

            get(size() - 1).next = newNode;

        } else {

            newNode.next = get(pos);

            get(pos - 1).next = newNode;

        }

    }

    public Node get(int pos) {

        if (pos < 0 || pos > size()) {

            throw new RuntimeException("下标错误");

        }

        if (pos == 0)

            return head;

        Node p = head;

        for (int i = 0; i < pos; i++)

            p = p.next;

        return p;

    }

    public static void main(String[] args) {

        MyList list = new MyList();

        list.insert(10, 0);

        list.insert(20, 1);

        list.insert(30, 0);

        list.insert(40, 1);

        System.out.println(list.size());

        list.bianli();

        System.out.println(list.isEmpty());

        System.out.println(list.get(2).data);

        list.clear();

        System.out.println(list.isEmpty());

    }

}