Flyweight（享元模式）

名  称 
Flyweight（享元模式） 

意  图 
运用共享技术有效地支持大量细粒度的对象。 

适  用 

环  境 
u       一个应用程序使用了大量的对象。 

u       完全由于使用大量的对象，造成很大的存储开销。 

u       对象的大多数状态都可变为外部状态。 

u       如果删除对象的外部状态，那么可以用相对较少的共享对象取代很多组对象。 

u       应用程序不依赖于对象标识。由于Flyweight对象可以被共享，对于概念上明显有别的对象，标识测试将返回真值。 

结  构 

享元模式要注意对象的内蕴模式和外蕴模式，从内蕴状态来看他们是同样的对象，但是不同的场合他们也会具体根据外晕模式做出相应的行为。

示例代码：

// package flyweight; abstract class FlyWeight { abstract public void operate(Character state); } // package flyweight; public class ConcreateFlyWeight extends FlyWeight { private Character intrinsicState = null; public ConcreateFlyWeight(Character state) { this.intrinsicState = state; } @Override public void operate(Character state) { System.out.println("intrinsic:" + intrinsicState + "/nextrinsic" + state); } } // package flyweight; import java.util.HashMap; import java.util.Iterator; import java.util.Map; import java.util.Map.Entry; public class FlyWeightFactory { private Map flies = new HashMap(); private FlyWeight lnkFlyWeight; public FlyWeightFactory() { } /** * 内蕴状态作为参数传入 */ public FlyWeight factory(Character state) { if (flies.containsKey(state)) { return (FlyWeight) flies.get(state); } else { FlyWeight flyWeight = new ConcreateFlyWeight(state); flies.put(state, flyWeight); return flyWeight; } } public void check() { FlyWeight fly = null; int i = 0; for (Iterator it = flies.entrySet().iterator(); it.hasNext();) { Entry e = (Entry) it.next(); System.out.println(e.getKey()); } } } // package flyweight; public class Main { public static void main(String[] args) { FlyWeightFactory factory = new FlyWeightFactory(); FlyWeight fly = factory.factory((new Character('a'))); fly.operate(new Character('1')); fly = factory.factory(new Character('b')); fly.operate(new Character('2')); fly = factory.factory(new Character('a')); fly.operate(new Character('3')); factory.check(); } }