重点概念
1. 这个模式相对简单。享元模式,就是在工厂中包含所要共享的元素实例,多个对象通过发给这个工厂所需要对象的标记,获得同一个实例,这样多个对象的操作只需要一个对象实例即可,看基础代码示例。
2. 内部状态(共享对象)和外部状态(个性化部分)(代码示例见后面网站第三版)
核心意思,是需要改变的内容部分,可以作为参数传递给方法,而对象本身依然是一个。
3. 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内存开销时可以考虑使用享元模式
4. 对象的大多数状态可以外部状态,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,此时可以考虑使用享元模式。
5. 享元模式节约内存开销,减少对象实例化个数。
示例程序
using System;
using System.Collections.Generic;
using System.Collections;
using System.Text;
namespace 享元模式
{
class Program
{
static void Main(string[] args)
{
int extrinsicstate = 22;
FlyweightFactory f = new FlyweightFactory();
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);
Console.Read();
}
}
class FlyweightFactory
{
private Hashtable flyweights = new Hashtable();
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]);
}
}
abstract class Flyweight
{
public abstract void Operation(int extrinsicstate);
}
class ConcreteFlyweight : Flyweight
{
public override void Operation(int extrinsicstate)
{
Console.WriteLine("具体Flyweight:" + extrinsicstate);
}
}
class UnsharedConcreteFlyweight : Flyweight
{
public override void Operation(int extrinsicstate)
{
Console.WriteLine("不共享的具体Flyweight:" + extrinsicstate);
}
}
}
网站,第三版
using System;
using System.Collections.Generic;
using System.Collections;
using System.Text;
namespace 享元模式
{
class Program
{
static void Main(string[] args)
{
WebSiteFactory f = new WebSiteFactory();
WebSite fx = f.GetWebSiteCategory("产品展示");
fx.Use(new User("小菜"));
WebSite fy = f.GetWebSiteCategory("产品展示");
fy.Use(new User("大鸟"));
WebSite fz = f.GetWebSiteCategory("产品展示");
fz.Use(new User("娇娇"));
WebSite fl = f.GetWebSiteCategory("博客");
fl.Use(new User("老顽童"));
WebSite fm = f.GetWebSiteCategory("博客");
fm.Use(new User("桃谷六仙"));
WebSite fn = f.GetWebSiteCategory("博客");
fn.Use(new User("南海鳄神"));
Console.WriteLine("得到网站分类总数为 {0}", f.GetWebSiteCount());
//string titleA = "大话设计模式";
//string titleB = "大话设计模式";
//Console.WriteLine(Object.ReferenceEquals(titleA, titleB));
Console.Read();
}
}
//用户
public class User
{
private string name;
public User(string name)
{
this.name = name;
}
public string Name
{
get { return name; }
}
}
//网站工厂
class WebSiteFactory
{
private Hashtable flyweights = new Hashtable();
//获得网站分类
public WebSite GetWebSiteCategory(string key)
{
if (!flyweights.ContainsKey(key))
flyweights.Add(key, new ConcreteWebSite(key));
return ((WebSite)flyweights[key]);
}
//获得网站分类总数
public int GetWebSiteCount()
{
return flyweights.Count;
}
}
//网站
abstract class WebSite
{
public abstract void Use(User user);
}
//具体的网站
class ConcreteWebSite : WebSite
{
private string name = "";
public ConcreteWebSite(string name)
{
this.name = name;
}
public override void Use(User user)
{
Console.WriteLine("网站分类:" + name + " 用户:" + user.Name);
}
}
}