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;}@Overridepublic 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();}}