New Features in C# 2.0—Generic Collection: How do I do that?

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How do I do that?

The easiest way to create a generic collection class is to create a specific collection (for example, one that holds integers) and then replace the type (for example, int) with the generic type (for example, T).

Thus:

private int data;

becomes:

private T data; // T is a generic Type Parameter 

The generic type parameter (in this case, T) is defined by you when you create your collection class by placing the type parameter inside angle brackets (< >):

public class Node<T>

Now you have defined a new type, "Node of T," which at runtime will become "Node of int" or node of any other type the compiler recognizes.

Example 1-2 creates a linked list of nodes of T, and then uses two instances of that generic list, each holding a different type of object.

Example 1-2. Creating your own generic collection

using System;
 
namespace GenericLinkedList
{
  public class Pilgrim
  {
    private string name;
    public Pilgrim(string name)
    {
      this.name = name;
    }
    public override string ToString( )
    {
      return this.name;
    }
  }
 
  public class Node<T>
  {
    // member fields
    private T data;
    private Node<T> next = null;
 
    // constructor
    public Node(T data)
    {
      this.data = data;
    }
 
    // properties
    public T Data { get { return this.data; } }
    public Node<T> Next
    {
      get { return this.next; }
    }
 
    // methods
    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;
    }
  } // end class
 
  public class LinkedList<T>
  {
    // member fields
    private Node<T> headNode = null;
 
    // properties
    // indexer
    public T this[int index]
    {
      get
      {
        int ctr = 0;
        Node<T> node = headNode;
        while (node != null && ctr <= index)
        {
          if (ctr = = index)
          {
            return node.Data;
          }
          else
          {
            node = node.Next;
          }
          ++ctr;
        } // end while
        throw new ArgumentOutOfRangeException( );
      } // end get
    } // end indexer
 
    // constructor
    public LinkedList( )
    {
    }
 
    // methods
    public void Add(T data)
    {
      if (headNode = = null)
      {
        headNode = new Node<T>(data);
      }
      else
      {
        headNode.Append(new Node<T>(data));
      }
    }
 
    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> myLinkedList = new LinkedList<int>( );
      for (int i = 0; i < 10; i++)
      {
        myLinkedList.Add(i);
      }
      Console.WriteLine("Integers: " + myLinkedList);
      LinkedList<Pilgrim> pilgrims = new LinkedList<Pilgrim>( );
      pilgrims.Add(new Pilgrim("The Knight"));
      pilgrims.Add(new Pilgrim("The Miller"));
      pilgrims.Add(new Pilgrim("The Reeve"));
      pilgrims.Add(new Pilgrim("The Cook"));
      Console.WriteLine("Pilgrims: " + pilgrims);
      Console.WriteLine("The fourth integer is " + myLinkedList[3]);
      Pilgrim d = pilgrims[1];
      Console.WriteLine("The second pilgrim is " + d);
    }
  }
}

Output:

Integers: 0, 1, 2, 3, 4, 5, 6, 7, 8, 9
Pilgrims: The Knight, The Miller, The Reeve, The Cook
The fourth integer is 3
The second pilgrim is The Miller