設(shè)計(jì)模式（15）---享元模式

2019-11-14 16:18:40

字體：大中小

來(lái)源：轉(zhuǎn)載

供稿：網(wǎng)友

一、定義

享元模式：運(yùn)用共享技術(shù)有效地支持大量細(xì)粒度的對(duì)象。

解釋：需要大量重復(fù)new一個(gè)對(duì)象時(shí)，使用享元模式可以讓你減少對(duì)象的初始化，從而減小內(nèi)存開銷。太蒼白了，理解的不到位，希望自己以后補(bǔ)充吧。

二、UML類圖及基本代碼

基本代碼：

public abstract class Flyweight    {        public abstract void Operation(int extrinsicstate);    }    public class ConcreteFlyweight : Flyweight    {        // 內(nèi)部狀態(tài)        PRivate string intrinsicstate;        // 構(gòu)造函數(shù)        public ConcreteFlyweight(string innerState)        {            this.intrinsicstate = innerState;        }        /// <summary>        /// 享元類的實(shí)例方法        /// </summary>        /// <param name="extrinsicstate">外部狀態(tài)</param>        public override void Operation(int extrinsicstate)        {            Console.WriteLine("具體實(shí)現(xiàn)類: intrinsicstate {0}, extrinsicstate {1}", intrinsicstate, extrinsicstate);        }    }public class FlyweightFactory    {        // 最好使用泛型Dictionary<string,Flyweighy>        //public Dictionary<string, Flyweight> flyweights = new Dictionary<string, Flyweight>();        public Hashtable flyweights = new Hashtable();        public FlyweightFactory()        {            flyweights.Add("A", new ConcreteFlyweight("A"));            flyweights.Add("B", new ConcreteFlyweight("B"));            flyweights.Add("C", new ConcreteFlyweight("C"));        }        public Flyweight GetFlyweight(string key)        {            // 更好的實(shí)現(xiàn)如下            //Flyweight flyweight = flyweights[key] as Flyweight;            //if (flyweight == null)            //{            // Console.WriteLine("駐留池中不存在字符串" + key);            // flyweight = new ConcreteFlyweight(key);            //}            //return flyweight;            return flyweights[key] as Flyweight;        }    }

客戶端調(diào)用：

class Program    {        static void Main(string[] args)        {            // 定義外部狀態(tài)，例如字母的位置等信息            int externalstate = 10;            // 初始化享元工廠            FlyweightFactory factory = new FlyweightFactory();            // 判斷是否已經(jīng)創(chuàng)建了字母A，如果已經(jīng)創(chuàng)建就直接使用創(chuàng)建的對(duì)象A            Flyweight fa = factory.GetFlyweight("A");            if (fa != null)            {                // 把外部狀態(tài)作為享元對(duì)象的方法調(diào)用參數(shù)                fa.Operation(--externalstate);            }            // 判斷是否已經(jīng)創(chuàng)建了字母B            Flyweight fb = factory.GetFlyweight("B");            if (fb != null)            {                fb.Operation(--externalstate);            }            // 判斷是否已經(jīng)創(chuàng)建了字母D            Flyweight fd = factory.GetFlyweight("D");            if (fd != null)            {                fd.Operation(--externalstate);            }            else            {                Console.WriteLine("駐留池中不存在字符串D");                // 這時(shí)候就需要?jiǎng)?chuàng)建一個(gè)對(duì)象并放入駐留池中                ConcreteFlyweight d = new ConcreteFlyweight("D");                factory.flyweights.Add("D", d);            }            Console.Read();        }    }

View Code

運(yùn)行結(jié)果：

三、具體實(shí)例：

構(gòu)建一個(gè)由不同用戶使用的通用網(wǎng)站，具體代碼如下：

public class User    {        private string name;        public string Name        {            get { return name; }        }        public User(string name)        {            this.name = name;        }    }    abstract class Website    {        public abstract void Use(User user);    }    class ConcreteWebsite : Website    {        private string name = "";        public ConcreteWebsite(string name)        {            this.name = name;        }        public override void Use(User user)        {            Console.WriteLine("website type:" + name + "user:" + user.Name);        }    }    class WebsiteFactory    {        private Hashtable flyweights = new Hashtable();        public Website GetWebsiteCategory(string key)        {            if (!flyweights.ContainsKey(key))            {                flyweights.Add(key, new ConcreteWebsite(key));            }            return ((Website)flyweights[key]);        }        public int GetWebsiteCount()        {            return flyweights.Count;        }    }

客戶端調(diào)用：

WebsiteFactory wf = new WebsiteFactory();            Website wx = wf.GetWebsiteCategory("show");            wx.Use(new User("a"));            Website wy = wf.GetWebsiteCategory("show");            wy.Use(new User("b"));            Website wz = wf.GetWebsiteCategory("see");            wz.Use(new User("c"));            Console.WriteLine("website type num:" + wf.GetWebsiteCount());