using System;

using System.Collections.Generic;

​

public interface IEbook

{

    string Filename {get;}

    void Show();

}

​

public class RealEbook: IEbook

{

    private string filename;

    public string Filename {

        get

        {

            return filename;

        }

    }

    public RealEbook(string filename)

    {

        this.filename = filename;

        Load();

    }

    private void Load()

    {

        Console.WriteLine("loading file");

    }

    public void Show()

    {

        Console.WriteLine("showing file");

    }

}

​

public class EbookProxy: IEbook

{

    private RealEbook ebook;

    private string filename;

    public string Filename

    {

        get

        {

            return filename;

        }

    }

    public EbookProxy(string filename)

    {

        this.filename = filename;

    }

    public void Show()

    {

        if(ebook == null)

            ebook = new RealEbook(filename);

        ebook.Show();

    }

}

​

public class Library

{

    private Dictionary<string, IEbook> ebooks = new Dictionary<string, IEbook>();

    public void Add(IEbook ebook)

    {

        ebooks.Add(ebook.Filename, ebook);

    }

    public void OpenEbook(string filename)

    {

        var ebook = ebooks[filename];

        ebook.Show();

    }

}

​

public class Program

{

    public static void Main()

    {

        var library = new Library();

        string[] filenames = {"a", "b", "c"};

        foreach(var filename in filenames)

        {

            library.Add(new EbookProxy(filename));

        }

        library.OpenEbook("a");

    }

}