副标题#e#
GOF：运用共享技能有效地支持大量细粒度的工具。
表明一下观念：也就是说在一个系统中假如有多个沟通的工具，那么只共享一份就可以了，不必每个都去实例化一个工具。好比说（这里引用GOF书中的例子）一个文本系统，每个字母定一个工具，那么巨细写字母一共就是52个，那么就要界说52个工具。假如有一个1M的文本，那么字母是何其的多，假如每个字母都界说一个工具那么内存早就爆了。那么假如要是每个字母都共享一个工具，那么就大大节省了资源。
在Flyweight模式中，由于要发生各类百般的工具，所以在Flyweight(享元)模式中常呈现Factory模式。Flyweight的内部状态是用来共享的,Flyweight factory认真维护一个工具存储池（Flyweight Pool）来存放内部状态的工具。Flyweight模式是一个提高措施效率和机能的模式,会大大加速措施的运行速度.应用场所许多，下面举个例子：
先界说一个抽象的Flyweight类：
package Flyweight;
public abstract class Flyweight
...
{
public abstract void operation();
}//end abstract class Flyweight
在实现一个详细类：
package Flyweight;
public class ConcreteFlyweight extends Flyweight
...
{
private String string;
public ConcreteFlyweight(String str)
...
{
string = str;
}//end ConcreteFlyweight(...)
public void operation()
...
{
System.out.println("Concrete---Flyweight : " + string);
}//end operation()
}//end class ConcreteFlyweight
实现一个工场要领类：
package Flyweight;
import java.util.Hashtable;
public class FlyweightFactory
...
{
private Hashtable flyweights = new Hashtable();//----------------------------1
public FlyweightFactory() ...{}
public Flyweight getFlyWeight(Object obj)
...
{
Flyweight flyweight = (Flyweight) flyweights.get(obj);//----------------2
if(flyweight == null) ...{//---------------------------------------------------3
//发生新的ConcreteFlyweight
flyweight = new ConcreteFlyweight((String)obj);
flyweights.put(obj, flyweight);//--------------------------------------5
}
return flyweight;//---------------------------------------------------------6
}//end GetFlyWeight(...)
public int getFlyweightSize()
...
{
return flyweights.size();
}
}//end class FlyweightFactory
#p#副标题#e#
这个工场要领类很是要害，这里具体表明一下：
在1处界说了一个Hashtable用来存储各个工具；在2处选出要实例化的工具，在6处将该工具返回，假如在Hashtable中没有要选择的工具，此时变量flyweight为null，发生一个新的flyweight存储在Hashtable中，并将该工具返回。
最后看看Flyweight的挪用：
package Flyweight;
import java.util.Hashtable;
public class FlyweightPattern ...{
FlyweightFactory factory = new FlyweightFactory();
Flyweight fly1;
Flyweight fly2;
Flyweight fly3;
Flyweight fly4;
Flyweight fly5;
Flyweight fly6;
/** *//** Creates a new instance of FlyweightPattern */
public FlyweightPattern() ...{
fly1 = factory.getFlyWeight("Google");
fly2 = factory.getFlyWeight("Qutr");
fly3 = factory.getFlyWeight("Google");
fly4 = factory.getFlyWeight("Google");
fly5 = factory.getFlyWeight("Google");
fly6 = factory.getFlyWeight("Google");
}//end FlyweightPattern()
public void showFlyweight()
...
{
fly1.operation();
fly2.operation();
fly3.operation();
fly4.operation();
fly5.operation();
fly6.operation();
int objSize = factory.getFlyweightSize();
System.out.println("objSize = " + objSize);
}//end showFlyweight()
public static void main(String[] args)
...
{
System.out.println("The FlyWeight Pattern!");
FlyweightPattern fp = new FlyweightPattern();
fp.showFlyweight();
}//end main(...)
}//end class FlyweightPattern
下面是运行功效：
Concrete---Flyweight : Google
Concrete---Flyweight : Qutr
Concrete---Flyweight : Google
Concrete---Flyweight : Google
Concrete---Flyweight : Google
Concrete---Flyweight : Google
objSize = 2
#p#分页标题#e#
我们界说了6个工具，个中有5个是沟通的，凭据Flyweight模式的界说“Google”应该共享一个工具，在实际的工具数中我们可以看出实际的工具却是只有2个。
下面给出一个浅易的UML图：
总结：
Flyweight(享元)模式是如此的重要，因为它能帮你在一个巨大的系统中大量的节减内存空间。在GOF的书中举了文本处理惩罚的例子，我以为很是得当。那么，在Java中String这个范例较量非凡，为什么呢，看下面的例子：
String a = "hello";
String b = "hello";
if(a == b)
System.out.println("OK");
else
System.out.println("Error");
输出功效是：OK。稍有履历的人都可以看出if条件较量的是两a和b的地点，也可以说是内存空间。那么Sting的实现是不是利用了Flyweight模式呢，不得而知，到此刻还没有研究过。
