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。Flyweight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:
public abstract class Flyweight { public abstract void operation(); }
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在实现一个具体类:
public class ConcreteFlyweight extends Flyweight { private String string; public ConcreteFlyweight(String str) { string = str; } public void operation() { System.out.println("Concrete---Flyweight : " + string); } }
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实现一个工厂方法类:
public class FlyweightFactory { private Hashtable flyweights = new Hashtable(); public FlyweightFactory(){} public Flyweight getFlyWeight(Object obj) { Flyweight flyweight = (Flyweight) flyweights.get(obj) if(flyweight == null) ...{ //产生新的ConcreteFlyweight flyweight = new ConcreteFlyweight((String)obj); flyweights.put(obj, flyweight); } return flyweight; } public int getFlyweightSize() { return flyweights.size(); } }
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最后看看Flyweight的调用:
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"); } public void showFlyweight() { fly1.operation(); fly2.operation(); fly3.operation(); fly4.operation(); fly5.operation(); fly6.operation(); int objSize = factory.getFlyweightSize(); System.out.println("objSize = " + objSize); } public static void main(String[] args) { System.out.println("The FlyWeight Pattern!"); FlyweightPattern fp = new FlyweightPattern(); fp.showFlyweight(); } }
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下面是运行结果:
Concrete---Flyweight : Google Concrete---Flyweight : Qutr Concrete---Flyweight : Google Concrete---Flyweight : Google Concrete---Flyweight : Google Concrete---Flyweight : Google objSize = 2
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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
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