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分类: Java

2008-12-02 16:54:02

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();
}

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);
 }
}

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();
 }
}

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();
 }
}

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

 

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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