Net设计模式实例之享元模式( Flyweight Pattern)

一、享元模式简介(Brief Introduction

享元模式(Flyweight Pattern,运用共享技术有效支持大量细粒度的对象。

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

享元模式可以避免大量非常相似类的开销。在程序设计中有时需要生成大量细粒度的类实例来表示数据。如果发现这些实例除了几个参数外基本伤都是相同的,有时就能够受大幅度第减少需要实例化的类的数量。如果能把这些参数移到类实例外面,在方法调用时将他们传递进来,就可以通过共享大幅度地减少单个实例的数目。

享元对象的内部状态与外部状态:

内部状态,在享元对象的内部并且不会随环境改变而改变的共享部分。

外部状态,随环境改变而改变的,不可以共享的状态。

二、解决的问题(What To Solve

       如果一个应用程序使用了大量的对象,而大量的这些对象造成了很大的存储开销,这时可以考虑使用享元模式。

       当对象的大多数状态是外部状态,如果删除对象的外部状态,那么可以用相对较少的共享对象取代很多组对象,这时也可以考虑使用享元模式。

三、享元模式分析(Analysis

1、享元模式结构

 

FlyweightFactory:享元工厂,用来创建和管理Flyweight对象。如果请求的Flyweight对象存在,怎返回已经存在的对象。否则新创建一个新的对象返回。

Flyweight:享元抽象类,通过这个接口,Flyweight可以接受并作用与外部状态。

UnsharedConcreteFlyweight:不需要共享的Flyweight子类。Flyweight接口并不强制共享。

ConcreteFlyweight:实现享元抽象类,为内部状态添加存储空间。

2、代码

1、享元工厂类FlyweightFactory

public class FlyweightFactory

{

    public Hashtable flyweights = new Hashtable();

 

    public FlyweightFactory()

    {

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

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

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

    }

 

    public Flyweight GetFlyweight(string key)

    {

        return flyweights[key] as Flyweight;

    }

}

 

2、享元抽象类Flyweight 及其具体实现类UnsharedConcreteFlyweight

ConcreteFlyweight

public abstract class Flyweight

{

    public abstract void Operation(int extrinsicstate);

}

 

public class UnsharedConcreteFlyweight:Flyweight

{

    public override void Operation(int extrinsicstate)

    {

        Console.WriteLine("{0}:{1}",this.GetType().Name,extrinsicstate);

    }

}

 

public class ConcreteFlyweight:Flyweight

{

    public override void Operation(int extrinsicstate)

    {

        Console.WriteLine("{0}:{1}", this.GetType().Name, extrinsicstate);

    }

}

 

3、客户端代码

static void Main(string[] args)

{

    // Arbitrary extrinsic state

    int extrinsicstate = 20;

    FlyweightFactory factory = new FlyweightFactory();

 

    // Work with different flyweight instances

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

    fx.Operation(--extrinsicstate);

 

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

    fy.Operation(--extrinsicstate);

 

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

    fz.Operation(--extrinsicstate);

 

    UnsharedConcreteFlyweight fu = new UnsharedConcreteFlyweight();

    fu.Operation(--extrinsicstate);

 

    Console.ReadKey();

}

3、实例运行结果

 

四.享元模式实例分析(Example

1、场景

一个文档Document中只有少数字符需要共享。结构如下图所示

 

CharacterFactory,享元工厂,用来创建和管理Charactor对象。如果请求的Charactor对象存在,怎返回已经存在的对象。否则新创建一个新的对象返回。

Character:享元抽象类,通过这个接口,Character可以接受并作用与外部状态。
CharacterA /CharacterB/CharacterC :实现享元抽象类,为内部状态添加存储空间。

2、代码

1字符工厂类CharacterFactory

class CharacterFactory

{

    private Dictionary<char, Character> _characters = new Dictionary<char, Character>();

    public Character GetCharacter(char key)

    {

        // Uses "lazy initialization"

        Character character = null;

        if (_characters.ContainsKey(key))

        {

            character = _characters[key];

        }

        else

        {

            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;

    }

}

 

2抽象数据对象类DataObject及其具体实现类CustomersData

/// <summary>

/// The 'Flyweight' abstract class

/// </summary>

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);

}

/// <summary>

/// A 'ConcreteFlyweight' class

/// </summary>

class CharacterA : Character

{

    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 + ")");

    }

}

/// <summary>

/// A 'ConcreteFlyweight' class

/// </summary>

class CharacterB : Character

{

    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.

/// <summary>

/// A 'ConcreteFlyweight' class

/// </summary>

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 + ")");

    }

}

 

3、客户端代码

static void Main(string[] args)

{

    // 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 c in chars)

    {

        pointSize++;

        Character character = factory.GetCharacter(c);

        character.Display(pointSize);

    }

    Console.ReadKey();

}

3、实例运行结果

五、总结(Summary

本文对享元模式(Flyweight Pattern)的概念、设计结构图、代码、使用场景、进行了描述。以一个享元模式实例进行了说明。如果一个应用程序使用了大量的对象,而大量的这些对象造成了很大的存储开销,这时可以考虑使用享元模式。

posted @ 2010-01-21 10:53  灵动生活  阅读(2431)  评论(4编辑  收藏