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 = http://www.mamicode.com/data;"hljs-keyword">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());
    }

}