File close

[srihariacha]

using System;
using System.IO;

class Program
{
    static void Main(string[] args)
    {
        FileDemo d = new FileDemo();
        d.Manipulate();
        Console.ReadLine();
    }
}

class FileDemo
{
    FileStream f;
    StreamReader r;
    StreamWriter w;

    public FileDemo()
    {
        f = new FileStream(@"E:\sri.txt", FileMode.OpenOrCreate, FileAccess.ReadWrite, FileShare.None);
        w = new StreamWriter(f);
        r = new StreamReader(f);
    }

    public void Manipulate()
    {
        w.Write("Hi");
        Console.WriteLine("Successfully written");
    }

    ~FileDemo()
    {
        f.Dispose();
        w.Dispose();//this program triggers exception  "cannot access closed file"
        r.Dispose();
    }
}