一个泛型的例题代码，看了有几点疑问，求解答

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace GenericSamp
{
    public class Student
    {
        private string StudentName;
        private int StudentAge;
        public Student(string name, int age)
        {
            this.StudentName = name;
            this.StudentAge = age;
        }
        public override string ToString()
        {
            return this.StudentName + ":年龄" + this.StudentAge + "岁";
        }
    }
    public class Node<T>
    {
        T data;
        Node<T> next;
        public Node(T data)
    {
        this.data=data;
        this.next=null;
    }
    public T Data{
    get {return this.data;}
    set{data=value;}
}
    public Node<T> Next{
    get{return this.next;}
    set{this.next=value;}

}
    public void Append(Node<T> newNode){
    if(this.next==null){this.next=newNode;}
    else{next.Append(newNode);}
}
    public override string ToString(){
    string output=data.ToString();
    if(next!=null){output+=","+next.ToString();}
    return output;
}
    }
    public class LinkedList<T>
    {
        Node<T> headNode = null;
        public void Add(T data)
        {
            if (headNode == null)
            {
                headNode = new Node<T>(data);
            }
            else
            {
                headNode.Append(new Node<T>(data));
            }
        }
        public T this[int index]
        {
            get
            {
                int temp = 0;
                Node<T> node = headNode;
                while (node != null && temp <= index)
                {
                    if (temp == index)
                    {
                        return node.Data;
                    }
                    else
                    {
                        node = node.Next;
                    }
                    temp++;
                }
                return default(T);

            }

        }
        public override string ToString()
        {
            if (this.headNode != null)
            {
                return this.headNode.ToString;
            }
            else
            {
                return string.Empty;
            }
        }

    }
    class Program
    {
        static void Main(string[] args)
        {
            LinkedList<int> intList=new LinkedList<int>();
            for (int i = 0; i < 5; i++)
            {
                intList.Add(i);
            }
            Console.WriteLine("整型List的内容为:" + intList);
            LinkedList<Student> StudentList = new LinkedList<Student>();
            StudentList.Add(new Student("张三",20));
            StudentList.Add(new Student("李四",22));
            StudentList.Add(new Student("王五",21));
            Console.WriteLine("Student类型List的内容为:" + StudentList);
        }
    }
}