Programming - Composite Structural Design Pattern

// Composite pattern -- Structural example

using System;
using System.Collections;

namespace DoFactory.GangOfFour.Composite.Structural
{

// MainApp test application

class MainApp
{
static void Main()
{
// Create a tree structure
Composite root = new Composite("root");
root.Add(new Leaf("Leaf A"));
root.Add(new Leaf("Leaf B"));

Composite comp = new Composite("Composite X");
comp.Add(new Leaf("Leaf XA"));
comp.Add(new Leaf("Leaf XB"));

root.Add(comp);
root.Add(new Leaf("Leaf C"));

// Add and remove a leaf
Leaf leaf = new Leaf("Leaf D");
root.Add(leaf);
root.Remove(leaf);

// Recursively display tree
root.Display(1);

// Wait for user
Console.Read();
}
}

// "Component"

abstract class Component
{
protected string name;

// Constructor
public Component(string name)
{
this.name = name;
}

public abstract void Add(Component c);
public abstract void Remove(Component c);
public abstract void Display(int depth);
}

// "Composite"

class Composite : Component
{
private ArrayList children = new ArrayList();

// Constructor
public Composite(string name) : base(name)
{
}

public override void Add(Component component)
{
children.Add(component);
}

public override void Remove(Component component)
{
children.Remove(component);
}

public override void Display(int depth)
{
Console.WriteLine(new String('-', depth) + name);

// Recursively display child nodes
foreach (Component component in children)
{
component.Display(depth + 2);
}
}
}

// "Leaf"

class Leaf : Component
{
// Constructor
public Leaf(string name) : base(name)
{
}

public override void Add(Component c)
{
Console.WriteLine("Cannot add to a leaf");
}

public override void Remove(Component c)
{
Console.WriteLine("Cannot remove from a leaf");
}

public override void Display(int depth)
{
Console.WriteLine(new String('-', depth) + name);
}
}
}

and

Output expected:

-root
---Leaf A
---Leaf B
---Composite X
-----Leaf XA
-----Leaf XB
---Leaf C