实现接口时提示异常public修饰符对此项无效

using System;

using System.Collections;

using System.Collections.Generic;

using System.Linq;

using System.Text;

using System.Threading.Tasks;


namespace _5._2创建泛型类

{

    class Program

    {

        //非泛型的简化链表类的创建

        public class LinkedListNode

        {

            public object Value { get;private set; }

            public LinkedListNode Next { get;internal set; }

            public LinkedListNode Prev { get; internal set; }

            public LinkedListNode(object value)

            {

                this.Value = value;

            }

        }


        public class LinkedList:IEnumerable

        {

            public LinkedListNode First { get; private set; }

            public LinkedListNode Last { get; private set; }

            public LinkedListNode AddList(object node)

            {

                var newnode = new LinkedListNode(node );

                if (First == null)

                {

                    First = newnode;

                    First.Prev = Last;

                    Last=First;

                }

                else

                {

                    Last.Next = newnode;

                    newnode.Prev = Last;

                    Last = newnode;

                }

                return newnode;

            }


            public IEnumerator GetEnumerator()

            {

                LinkedListNode current =First;

                while (current !=null )

                {

                    yield return current.Value;

                    current = current.Next;

                }

            }

        }

        //创建链表的泛型版本

        public class LinkListNode <T>

        {

            public T Value { get;private set; }

            public LinkListNode(T value)

            {

                this.Value = value;

            }

            public LinkListNode<T> Next { get; internal set; }