Java设计模式之Flyweight模式.ppt

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1、Java设计模式之Flyweight模式 GOF：运用共享技术有效地支持大量细粒度的对象。解释一下概念：也就是说在一个系统中如果有多个相同的对象，那么只共享一份就可以了，不必每个都去实例化一个对象。比如说（这里引用GOF书中的例子）一个文本系统，每个字母定一个对象，那么大小写字母一共就是52个，那么就要定义 52个对象。如果有一个1M的文本，那么字母是何其的多，如果每个字母都定义一个对象那么内存早就爆了。那么如果要是每个字母都共享一个对象，那么就大大节约了资源。在Flyweight模式中，由于要产生各种各样的对象，所以在Flyweight(享元)模式中常出现Factory 模式。Flyweig

2、ht的内部状态是用来共享的,Flyweight factory负责维护一个对象存储池（Flyweight Pool）来存放内部状态的对象。Flyweight模式是一个提高程序效率和性能的模式,会大大加快程序的运行速度.应用场合很多，下面举个例子：先定义一个抽象的Flyweight类：package Flyweight;public abstract class Flyweight.public abstract void operation();/end abstract class Flyweight 在实现一个具体类：package Flyweight;public class Concr

3、eteFlyweight 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 实现一个工厂方法类：package Flyweight;import java.util.Hashtable;pub

4、lic class FlyweightFactory.private Hashtable flyweights=new Hashtable();/-1public FlyweightFactory().public Flyweight getFlyWeight(Object obj).Flyweight flyweight=(Flyweight)flyweights.get(obj);/-2if(flyweight=null)./-3/产生新的ConcreteFlyweightflyweight=new ConcreteFlyweight(String)obj);flyweights.put(

5、obj,flyweight);/-5return flyweight;/-6/end GetFlyWeight(.)public int getFlyweightSize().return flyweights.size();/end class FlyweightFactory这个工厂方法类非常关键，这里详细解释一下：在1处定义了一个Hashtable用来存储各个对象；在2处选出要实例化的对象，在6处将该对象返回，如果在Hashtable中没有要选择的对象，此时变量flyweight为null，产生一个新的flyweight存储在Hashtable中，并将该对象返回。最后看看Flyweigh

6、t的调用：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=fac

7、tory.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

8、.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(.)/en

9、d class FlyweightPattern下面是运行结果：Concrete-Flyweight:GoogleConcrete-Flyweight:QutrConcrete-Flyweight:GoogleConcrete-Flyweight:GoogleConcrete-Flyweight:GoogleConcrete-Flyweight:GoogleobjSize=2 我们定义了6个对象，其中有5个是相同的，按照Flyweight模式的定义“Google”应该共享一个对象，在实际的对象数中我们可以看出实际的对象却是只有2个。下面给出一个简易的UML图：总结：Flyweight(享元)模式是如此的重要，因为它能帮你在一个复杂的系统中大量的节省内存空间。在GOF的书中举了文本处理的例子，我觉得非常恰当。那么，在Java中String这个类型比较特殊，为什么呢，看下面的例子：String a=hello;String b=hello;if(a=b)System.out.println(OK);elseSystem.out.println(Error);更多资料 java培训 http:/