享元模式（Flyweight）

1.    定义

       运用共享技术有效地支持大量细粒度的对象。

2.      UML 类图

 

3.      结构代码

// Flyweight pattern -- Structural example

using System;

using System.Collections;

 

namespace DoFactory.GangOfFour.Flyweight.Structural

{

  ///<summary>

  /// MainApp startup class for Structural

  /// Flyweight Design Pattern.

  ///</summary>

  classMainApp

  {

    ///<summary>

    /// Entry point into console application.

    ///</summary>

    staticvoid Main()

    {

      // Arbitrary extrinsic state

      int extrinsicstate = 22;

 

      FlyweightFactory factory =new FlyweightFactory();

 

      // Work with different flyweight instances

      Flyweight fx = factory.GetFlyweight("X");

      fx.Operation(--extrinsicstate);

 

      Flyweight fy = factory.GetFlyweight("Y");

      fy.Operation(--extrinsicstate);

 

      Flyweight fz = factory.GetFlyweight("Z");

      fz.Operation(--extrinsicstate);

 

      UnsharedConcreteFlyweight fu =new

        UnsharedConcreteFlyweight();

 

      fu.Operation(--extrinsicstate);

 

      // Wait for user

      Console.ReadKey();

    }

  }

 

  ///<summary>

  /// The 'FlyweightFactory' class

  ///</summary>

  classFlyweightFactory

  {

    privateHashtable flyweights = new Hashtable();

 

    // Constructor

    public FlyweightFactory()

    {

      flyweights.Add("X",new ConcreteFlyweight());

      flyweights.Add("Y",new ConcreteFlyweight());

      flyweights.Add("Z",new ConcreteFlyweight());

    }

 

    publicFlyweight GetFlyweight(string key)

    {

      return ((Flyweight)flyweights[key]);

    }

  }

 

  ///<summary>

  /// The 'Flyweight' abstract class

  ///</summary>

  abstractclass Flyweight

  {

    publicabstract void Operation(int extrinsicstate);

  }

 

  ///<summary>

  /// The 'ConcreteFlyweight' class

  ///</summary>

  classConcreteFlyweight : Flyweight

  {

    publicoverride void Operation(int extrinsicstate)

    {

      Console.WriteLine("ConcreteFlyweight: " + extrinsicstate);

    }

  }

 

  ///<summary>

  /// The 'UnsharedConcreteFlyweight' class

  ///</summary>

  classUnsharedConcreteFlyweight : Flyweight

  {

    publicoverride void Operation(int extrinsicstate)

    {

      Console.WriteLine("UnsharedConcreteFlyweight: " +

        extrinsicstate);

    }

  }

}

Output

ConcreteFlyweight: 21
ConcreteFlyweight: 20
ConcreteFlyweight: 19
UnsharedConcreteFlyweight: 18

4.      实例代码

// Flyweight pattern -- Real World example

using System;

using System.Collections.Generic;

 

namespace DoFactory.GangOfFour.Flyweight.RealWorld

{

  ///<summary>

  /// MainApp startup class for Real-World

  /// Flyweight Design Pattern.

  ///</summary>

  classMainApp

  {

    ///<summary>

    /// Entry point into console application.

    ///</summary>

    staticvoid Main()

    {

      // Build a document with text

      string document ="AAZZBBZB";

      char[] chars = document.ToCharArray();

 

      CharacterFactory factory =new CharacterFactory();

 

      // extrinsic state

      int pointSize = 10;

 

      // For each character use a flyweight object

      foreach (char cin chars)

      {

        pointSize++;

        Character character = factory.GetCharacter(c);

        character.Display(pointSize);

      }

 

      // Wait for user

      Console.ReadKey();

    }

  }

 

  ///<summary>

  /// The 'FlyweightFactory' class

  ///</summary>

  classCharacterFactory

  {

    privateDictionary<char,Character> _characters =

      newDictionary<char,Character>();

 

    publicCharacter GetCharacter(char key)

    {

      // Uses "lazy initialization"

      Character character =null;

      if (_characters.ContainsKey(key))

      {

        character = _characters[key];

      }

      else

      {

        switch (key)

        {

          case'A': character = newCharacterA(); break;

          case'B': character = newCharacterB(); break;

          //...

          case'Z': character = newCharacterZ(); break;

        }

        _characters.Add(key, character);

      }

      return character;

    }

  }

 

  ///<summary>

  /// The 'Flyweight' abstract class

  ///</summary>

  abstractclass Character

  {

    protectedchar symbol;

    protectedint width;

    protectedint height;

    protectedint ascent;

    protectedint descent;

    protectedint pointSize;

 

    publicabstract void Display(int pointSize);

  }

 

  ///<summary>

  /// A 'ConcreteFlyweight' class

  ///</summary>

  classCharacterA : Character

  {

    // Constructor

    public CharacterA()

    {

      this.symbol ='A';

      this.height = 100;

      this.width = 120;

      this.ascent = 70;

      this.descent = 0;

    }

 

    publicoverride void Display(int pointSize)

    {

      this.pointSize = pointSize;

      Console.WriteLine(this.symbol +

        " (pointsize " +this.pointSize + ")");

    }

  }

 

  ///<summary>

  /// A 'ConcreteFlyweight' class

  ///</summary>

  classCharacterB : Character

  {

    // Constructor

    public CharacterB()

    {

      this.symbol ='B';

      this.height = 100;

      this.width = 140;

      this.ascent = 72;

      this.descent = 0;

    }

 

    publicoverride void Display(int pointSize)

    {

      this.pointSize = pointSize;

      Console.WriteLine(this.symbol +

        " (pointsize " +this.pointSize + ")");

    }

 

  }

 

  // ... C, D, E, etc.

 

  ///<summary>

  /// A 'ConcreteFlyweight' class

  ///</summary>

  classCharacterZ : Character

  {

    // Constructor

    public CharacterZ()

    {

      this.symbol ='Z';

      this.height = 100;

      this.width = 100;

      this.ascent = 68;

      this.descent = 0;

    }

 

    publicoverride void Display(int pointSize)

    {

      this.pointSize = pointSize;

      Console.WriteLine(this.symbol +

        " (pointsize " +this.pointSize + ")");

    }

  }

}

Output

A (pointsize 11)
A (pointsize 12)
Z (pointsize 13)
Z (pointsize 14)
B (pointsize 15)
B (pointsize 16)
Z (pointsize 17)
B (pointsize 18)

该文章来自：http://www.dofactory.com/Patterns/PatternFlyweight.aspx