using System;
 
public class DocumentWriter
{
    public void CreateDocument()
    {
       CreatePage();
    }
 
    protected virtual void CreatePage()
    {
        System.Console.WriteLine("DocumentWriter.CreatePage()");
    }
}
 
public class PdfDocumentWriter : DocumentWriter
{
    protected override void CreatePage()
    {
        System.Console.WriteLine("PdfDocumentWriter.CreatePage()");
    }
}
 
public class HtmlDocumentWriter : DocumentWriter
{
    protected override void CreatePage()
    {
        System.Console.WriteLine("HtmlDocumentWriter.CreatePage()");
    }
}
 
public static class Program
{
    public static void Main()
    {
        DocumentWriter documentWriter = new PdfDocumentWriter();
        documentWriter.CreateDocument();
 
        // Re-use the same variable. 
        // CreateDocumentwill still call the correct version of CreatePage.
        documentWriter = new HtmlDocumentWriter();
        documentWriter.CreateDocument();
    }
}

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