Flyweight Design Pattern in C#

Uses sharing to support large numbers of fine-grained objects efficiently.

This structural code demonstrates the Flyweight pattern in which a relatively small number of objects is shared many times by different clients.

using System;
using System.Collections;

  class MainApp
  {
    static void Main()
    {
      // Arbitrary extrinsic state 
      int extrinsicstate = 22;
 
      FlyweightFactory f = new FlyweightFactory();

      // Work with different flyweight instances 
      Flyweight fx = f.GetFlyweight("X");
      fx.Operation(--extrinsicstate);

      Flyweight fy = f.GetFlyweight("Y");
      fy.Operation(--extrinsicstate);

      Flyweight fz = f.GetFlyweight("Z");
      fz.Operation(--extrinsicstate);

      UnsharedConcreteFlyweight uf = new 
        UnsharedConcreteFlyweight();

      uf.Operation(--extrinsicstate);

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

  // "FlyweightFactory" 
  class FlyweightFactory 
  {
    private Hashtable flyweights = new Hashtable();

    // Constructor 
    public FlyweightFactory()
    {
      flyweights.Add("X", new ConcreteFlyweight());    
      flyweights.Add("Y", new ConcreteFlyweight());
      flyweights.Add("Z", new ConcreteFlyweight());
    }

    public Flyweight GetFlyweight(string key)
    {
      return((Flyweight)flyweights[key]); 
    }
  }

  // "Flyweight" 
  abstract class Flyweight 
  {
    public abstract void Operation(int extrinsicstate);
  }

  // "ConcreteFlyweight" 

  class ConcreteFlyweight : Flyweight
  {
    public override void Operation(int extrinsicstate)
    {
      Console.WriteLine("ConcreteFlyweight: " + extrinsicstate);
    }
  }

  // "UnsharedConcreteFlyweight" 
  class UnsharedConcreteFlyweight : Flyweight
  {
    public override void Operation(int extrinsicstate)
    {
      Console.WriteLine("UnsharedConcreteFlyweight: " + 
        extrinsicstate);
    }
  }