LinkedList on page 110 C#4 2010 Wrox

amigo1 · November 28th, 2012, 02:21 AM

Code:

// this program is the program on page 110 C#4 2010 Wrox
// it deals with the creation of a linkedlist-----.
using System;
using System.Collections;
using System.Linq;
using System.Text;

namespace scratch_pad_2
{
    class Program
    {

        static void Main(string[] args)
        {
            var list1 = new LinkedList();
            list1.AddLast(2);
            list1.AddLast(4);
            list1.AddLast(6);
            foreach (int i in list1)
            {
                Console.WriteLine(i);
                Console.Read();
            }
        }
    }

    public class LinkedListNode 
    {
        public LinkedListNode(object value)
        {
            this.Value = value;
        }
        public object Value { get; private set; }
        public LinkedListNode Next { get; internal set; }
        public LinkedListNode Prev { get; internal set; }
    }
     public class LinkedList 
   // public class LinkedList : IEnumerable
    //     note that both the above statements are valid
    {
        public LinkedListNode First { get; private set; }
        public LinkedListNode Last { get; private set; }
        public LinkedListNode AddLast(object node)
        {
            var newNode = new LinkedListNode(node);
            if (First == null) { First = newNode; Last = First; }
            else
            { Last.Next = newNode; Last = newNode; }
            return newNode;        
        }
        public IEnumerator GetEnumerator()
        {
            LinkedListNode current = First;
// current here is an identifier/variable

            while (current != null) { yield return current.Value;
            current = current.Next;
            }
        }
        
    }
}

Q1 ] How does the internal keyword work here?
Q2] How to make use of the Prev property?
Q3] In this statement :
public object Value { get; private set; }
why the type is âobjectâ instead of â LinkedListNode â
Q4] Should we remember such programs ?
Q5] Is there any class called âLinkedListâ ? I know there is a class called âLinkedList<T>â , so that the transition to such a class (âLinkedList<T>â ) in the next section of the chapter would create a system class overlap , --- actually If you may please explain this area

ChristianNagel · November 28th, 2012, 03:48 AM

Quote:

Originally Posted by amigo1

Q1 ] How does the internal keyword work here?
Q2] How to make use of the Prev property?
Q3] In this statement :
public object Value { get; private set; }
why the type is âobjectâ instead of â LinkedListNode â
Q4] Should we remember such programs ?
Q5] Is there any class called âLinkedListâ ? I know there is a class called âLinkedList<T>â , so that the transition to such a class (âLinkedList<T>â ) in the next section of the chapter would create a system class overlap , --- actually If you may please explain this area

That many questions ;-)
Q1: internal works here the same as on other places. Using internal with the set accessor of the property, only code within the assembly is allowed to access this property accessor.
Q2: Do you mean this?

Code:

var node = myLinkedList.Prev;

Q3: Because the Value property is used to access the object that is kept with the LinkedListNode.
Q4: why not? Of course it's better to use generic types instead of object types, but I guess this sample leads you in that way and makes a comparision later on.
Q5: There is a LinkedList<T>, as you know already. There is no overlap as one type is non-generic, and the other one is generic, and they are also in different namespaces. Of course as there is a LinkedList<T> class in the Framework there's no need to create a custom one. However, it's good to know how this works to build something similar, and to know what's behind the LinkedList<T> class.

amigo1 · November 30th, 2012, 02:29 AM

thank you teacher --- its been a long time that we had spoken
how are you?
regards
amigo1