C#

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Windows.Forms;

namespace WindowsFormsApplication1
{
    public partial class Form1 : Form
    {
        System.Collections.ArrayList tabpages = new System.Collections.ArrayList();
        System.Collections.ArrayList webpages = new System.Collections.ArrayList();

        int current_tab_count = 0;          // Keep track of how many tabs there are..


        public Form1()
        {
            InitializeComponent();
            tabControl1.TabPages.Clear();                // Get rid of any existing pages in the tab control
            Create_a_new_tab();                          // This method creates a new tab, new webbrowser and opens the default page.
            WebBrowser webpage = GetCurrentWebBrowser();
            webpage.GoHome();
        }

        private void toolStripButton5_Click(object sender, EventArgs e)
        {
            // Go Home - go to the default home page.
            WebBrowser thiswebpage = GetCurrentWebBrowser();
            thiswebpage.GoHome();
            timer1.Enabled = true;  // Start the animation timer
        }

        private void button_back_Click(object sender, EventArgs e)
        {
            // Go Back - if the web control can go back, do it.
            WebBrowser thiswebpage = GetCurrentWebBrowser();
            if (thiswebpage.CanGoBack)
                thiswebpage.GoBack();
        }

        private void toolStripButton4_Click(object sender, EventArgs e)
        {
            // Refresh - cause the browser to reload and redisplay the current page
            WebBrowser thiswebpage = GetCurrentWebBrowser();
            thiswebpage.Refresh();
            timer1.Enabled = true;  // Start the animation timer
        }

        private void toolStripButton2_Click(object sender, EventArgs e)
        {
            // Go Forward - if the web control cna go forward, do it.
            WebBrowser thiswebpage = GetCurrentWebBrowser();
            if (thiswebpage.CanGoForward)
                thiswebpage.GoForward();
        }

        private void toolStripButton3_Click(object sender, EventArgs e)
        {
            WebBrowser thiswebpage = GetCurrentWebBrowser();
            thiswebpage.Stop();
        }

        private void toolStripButton6_Click(object sender, EventArgs e)
        {
            // The user has clicked on the GO button next to the Address text box, so
            // open the URL address in this page

            string url = toolStripComboBox1.Text;
            if (url == "") return;                              // Return if nowhere to go
            WebBrowser thiswebpage = GetCurrentWebBrowser();    // Get the currently displayed WebBrowser
            thiswebpage.Navigate(url);                          // Get the URL from the control, and send the WebBrowser to fetch and display it
            timer1.Enabled = true;                              // Start the animation
        }
        private void toolStripComboBox1_KeyPress(object sender, KeyEventArgs e)
        {
            // Check to see if user has pressed return and if they have, perform the 
            // same actions as if the GO button was clicked.
            if (e.KeyCode == Keys.Enter) toolStripButton6.PerformClick();
        }

        private void toolStripComboBox1_SelectedIndexChanged(object sender, EventArgs e)
        {
            // The user selected an item from the drop down list, so
            // go to that website by programmatically clicking the GO button.
            toolStripButton6.PerformClick();
        }

       
        private void Create_a_new_tab()
        {
            // Add a new tab control, and put a web control in it.
            // Let's have a maxium of 10 tabs to keep things sane.

            if (current_tab_count == 10) return;

            // Create the new tab page
            TabPage newpage = new TabPage("Loading...");    // Create the new page
            tabpages.Add(newpage);                          // Add the page to an arraylist to keep track of it.
            tabControl1.TabPages.Add(newpage);              // Add the page to the TabControl so it actually appears

            // Keep track of how many pages are open.
            current_tab_count++;

            // Create a new WebBrowser control.
            WebBrowser webpage = new WebBrowser();          // Create the new control
            webpages.Add(webpage);                          // Add the control to an arraylist to keep track of it.
            webpage.Parent = newpage;                       // Make sure the WebControl's parent is the TabControl page
            webpage.Dock = DockStyle.Fill;                  // Make the WebControl fill the entire TabControl page.

            // We define a handler to perform some actions when the document has been fetched and displayed.
            // We need to do this as the WebControl will work in the background, and we need to know when it has
            // finished so we can switch off the animation timer, and update the name of the Tab with the
            // the document title.
            webpage.DocumentCompleted += new WebBrowserDocumentCompletedEventHandler(webpage_DocumentCompleted);
            // webpage.GoHome();                               // Display the default page.
            timer1.Enabled = true;                          // Start the timer for animating the little logo in the top right.

            // Bring the new page to the foreground
            tabControl1.SelectedTab = newpage;

        }

        private WebBrowser GetCurrentWebBrowser()
        {
            // This method returns the currently display WebControl.
            // We use an arraylist of webpages, and find the right one by getting the index
            // of the current tab.

            TabPage current_tab = tabControl1.SelectedTab;
            WebBrowser thiswebpage = (WebBrowser)webpages[tabpages.IndexOf(current_tab)];
            return thiswebpage;
        }

        private void UpdateAllNames()
        {
            // Update all the tab names for all the currently open web pages.

            foreach (TabPage tb in tabControl1.TabPages)
            {
                UpdateName(tb);
            }
        }

        void webpage_DocumentCompleted(object sender, WebBrowserDocumentCompletedEventArgs e)
        {
            // This method is called when a webpage has completed rendering.
            // It's called because we asked the WebControl send this message.
            // See the CreateNewTab method

            UpdateAllNames();               // Update the names of the tabs by looking at the HTML document title.
            UpdateBackForwardButtons();     // Make sure the back and forward buttons are disabled if actions are not possible
            timer1.Enabled = false;         // Stop the animation
        }

        private void UpdateBackForwardButtons()
        {
            // Update the state of the buttons (i.e. ghosted or not)
            // dpending on if the webbrowser control can go back, forward etc.

            WebBrowser thiswebpage = GetCurrentWebBrowser();

            if (thiswebpage.CanGoBack) button_back.Enabled = true;
            else button_back.Enabled = false;

            if (thiswebpage.CanGoForward) toolStripButton2.Enabled = true;
            else toolStripButton2.Enabled = false;

            if (current_tab_count > 1) closeCurrentTabToolStripMenuItem.Enabled = true;
            else closeCurrentTabToolStripMenuItem.Enabled = false;
        }

        private void tabControl1_Selected(object sender, TabControlEventArgs e)
        {
            // This is called when a new tab page is made active.
            // We don't need to do much - the webbrowser control will automatically be
            // brought to the forground - but we do need to make sure the buttons
            // for Back and Forward reflect this particular page.

            UpdateBackForwardButtons();
        }

        private void menuStrip1_ItemClicked(object sender, ToolStripItemClickedEventArgs e)
        {

        }

        private void closeCurrentTabToolStripMenuItem_Click(object sender, EventArgs e)
        {

        }

        private void UpdateName(TabPage tb)
        {
            // Update the name of the current tab by looking
            // at the document it is displayed

            TabPage current_tab = tb;
            WebBrowser thiswebpage = (WebBrowser)webpages[tabpages.IndexOf(current_tab)];

            if (thiswebpage.Document != null)
                current_tab.Text = thiswebpage.Document.Title;
            else
                current_tab.Text = "Zzz";
        }

        private void newTabToolStripMenuItem_Click(object sender, EventArgs e)
        {
            Create_a_new_tab();

            WebBrowser thiswebpage = GetCurrentWebBrowser();
            if (toolStripComboBox1.Text == "")
                thiswebpage.GoHome();
            else
            thiswebpage.Navigate(toolStripComboBox1.Text);
        }

        private void webBrowser1_DocumentCompleted(object sender, WebBrowserDocumentCompletedEventArgs e)
        {

        }

        private void tabPage2_Click(object sender, EventArgs e)
        {

        }

    }
}

class A
{
  public A() { }
  protected virtual void MakeLunch()
  {
    //Make cheese sandwich
  }
}
.
class B : A
{
  public B() { }
  protected override void MakeLunch()
  {
    base.MakeLunch();
    //Grab a banana
  }
}
.
class C : B
{
  public C() { }
  protected override void MakeLunch()
  {
    A.MakeLunch();
    //Get a drink
  }
}