C#

using System;
using System.Collections.Generic;

public abstract class ZooAnimal
{
    public abstract string Speak();
}

public class Cat : ZooAnimal
{
    public override string Speak()
    {
        return "Meow";
    }
}

public class Lion : Cat
{
    public override string Speak()
    {
        return "Rowr!";
    }
}

public class Program
{
    public static void Main(params string[] args)
    {
        List<ZooAnimal> zooAnimals = new List<ZooAnimal>();

        for (int i = 0; i < 2; i++)
            zooAnimals.Add(new Cat());

        for (int i = 0; i < 3; i++)
            zooAnimals.Add(new Lion());

        for (int i = 0; i < zooAnimals.Count; i++)
        {
            Lion lion = zooAnimals[i] as Lion;

            if (lion != null)
                Console.WriteLine("The lion says: " + lion.Speak());
            else
            {
                Cat cat = zooAnimals[i] as Cat;
                Console.WriteLine("The cat says: " + cat.Speak());
            }
        }

        Console.Read();
    }
}

new Rectangle(this.Left, this.Top, this.Width, this.Height);

cor2879 wrote:

So just create an overloaded class, call it WidgetCollection or something like that. This class will inherit from List<widget> and also contain an instance of the StateTracker class

private void ShowNewForm(object sender, EventArgs e)
{
    Form childForm = new Form();
    childForm.MdiParent = this;
    this.Text = "Parent form heading";
    childForm.Show();
}

You wrote:

child file name