Flyweight

// Flyweight pattern -- Real World example

using System;
using System.Collections;

namespace DoFactory.GangOfFour.Flyweight.RealWorld
{

  // MainApp test application

  class MainApp
  {
    static void Main()
    {
      // Build a document with text
      string document = "AAZZBBZB";
      char[] chars = document.ToCharArray();

      CharacterFactory f = new CharacterFactory();

      // extrinsic state
      int pointSize = 10;

      // For each character use a flyweight object
      foreach (char c in chars)
      {
        pointSize++;
        Character character = f.GetCharacter(c);
        character.Display(pointSize);
      }

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

  // "FlyweightFactory"

  class CharacterFactory
  {
    private Hashtable characters = new Hashtable();

    public Character GetCharacter(char key)
    {
      // Uses "lazy initialization"
      Character character = characters[key] as Character;
      if (character == null)
      {
        switch (key)
        {
          case 'A': character = new CharacterA(); break;
          case 'B': character = new CharacterB(); break;
            //...
          case 'Z': character = new CharacterZ(); break;
        }
        characters.Add(key, character);
      }
      return character;
    }
  }

  // "Flyweight"

  abstract class Character
  {
    protected char symbol;
    protected int width;
    protected int height;
    protected int ascent;
    protected int descent;
    protected int pointSize;

    public abstract void Display(int pointSize);
  }

  // "ConcreteFlyweight"

  class CharacterA : Character
  {
    // Constructor
    public CharacterA()
    {
      this.symbol = 'A';
      this.height = 100;
      this.width = 120;
      this.ascent = 70;
      this.descent = 0;
    }

    public override void Display(int pointSize)
    {
      this.pointSize = pointSize;
      Console.WriteLine(this.symbol +
        " (pointsize " + this.pointSize + ")");
    }
  }

  // "ConcreteFlyweight"

  class CharacterB : Character
  {
    // Constructor
    public CharacterB()
    {
      this.symbol = 'B';
      this.height = 100;
      this.width = 140;
      this.ascent = 72;
      this.descent = 0;
    }

    public override void Display(int pointSize)
    {
      this.pointSize = pointSize;
      Console.WriteLine(this.symbol +
        " (pointsize " + this.pointSize + ")");
    }

  }

  // ... C, D, E, etc.

  // "ConcreteFlyweight"

  class CharacterZ : Character
  {
    // Constructor
    public CharacterZ()
    {
      this.symbol = 'Z';
      this.height = 100;
      this.width = 100;
      this.ascent = 68;
      this.descent = 0;
    }

    public override void Display(int pointSize)
    {
      this.pointSize = pointSize;
      Console.WriteLine(this.symbol +
        " (pointsize " + this.pointSize + ")");
    }
  }
}