Composite

// Composite pattern -- Real World example

using System; using System.Collections; namespace DoFactory.GangOfFour.Composite.RealWorld {       // Mainapp test application    class MainApp   {      static void Main()     {        // Create a tree structure       CompositeElement root =          new CompositeElement("Picture");       root.Add( new PrimitiveElement("Red Line"));       root.Add( new PrimitiveElement("Blue Circle"));       root.Add( new PrimitiveElement("Green Box"));       CompositeElement comp =          new CompositeElement("Two Circles");       comp.Add( new PrimitiveElement("Black Circle"));       comp.Add( new PrimitiveElement("White Circle"));       root.Add(comp);        // Add and remove a PrimitiveElement       PrimitiveElement pe =          new PrimitiveElement("Yellow Line");       root.Add(pe);       root.Remove(pe);        // Recursively display nodes       root.Display(1);        // Wait for user       Console.Read();     }   }    // "Component" Treenode    abstract class DrawingElement   {      protected string name;      // Constructor      public DrawingElement( string name)     {        this.name = name;     }      public abstract void Add(DrawingElement d);      public abstract void Remove(DrawingElement d);      public abstract void Display( int indent);   }    // "Leaf"    class PrimitiveElement : DrawingElement   {      // Constructor      public PrimitiveElement( string name) : base(name)     {       }      public override void Add(DrawingElement c)     {       Console.WriteLine(         "Cannot add to a PrimitiveElement");     }      public override void Remove(DrawingElement c)     {       Console.WriteLine(         "Cannot remove from a PrimitiveElement");     }      public override void Display( int indent)     {       Console.WriteLine(          new String('-', indent) + " " + name);     }   }    // "Composite"    class CompositeElement : DrawingElement   {      private ArrayList elements = new ArrayList();         // Constructor      public CompositeElement( string name) : base(name)     {       }      public override void Add(DrawingElement d)     {       elements.Add(d);     }      public override void Remove(DrawingElement d)     {       elements.Remove(d);     }      public override void Display( int indent)     {       Console.WriteLine( new String('-', indent) +         "+ " + name);        // Display each child element on this node        foreach (DrawingElement c in elements)       {         c.Display(indent + 2);       }     }   } }