Flyweight(享元)模式.docVIP

设计模式----Flyweight(享元)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。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：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?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实现一个工厂方法类：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????????????//产生新的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Ha