享元模式

定义：

运用共享技术有效地支持大量细粒度的对象。

适用性：

1.一个应用程序使用了大量的对象，造成很大的存储开销。

2.对象大多数状态都可变为外部状态。

3,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对组对象。

4.应用程序不依赖对象标识。由于享元模式对象可以被共享，对于概念上明显有别的对象，标识测试将返回真值。

类图：

package designPatterns;import java.util.HashMap;import java.util.Map;interface Flyweight{//描述一个接口，通过这个接口flyweight可以接受并作用于外部状态。public void action(int arg);}class FlyweightImpl implements Flyweight{//实现flyweight接口，并为内部状态（如果有的话）增加存储空间。public void action(int arg) {System.out.println("argument: "+arg);}}class FlyweightFactory{private static Map flyweights = new HashMap();public FlyweightFactory(String arg){flyweights.put(arg, new FlyweightImpl());}public static Flyweight getFlyweight(String key){if(flyweights.get(key) == null){flyweights.put(key, new FlyweightImpl());}return (Flyweight) flyweights.get(key);}public static int getSize(){return flyweights.size();}}/** * @author sky * */public class FlyWeightTest {public static void main(String[] args) {Flyweight fly1 = FlyweightFactory.getFlyweight("a");fly1.action(1);Flyweight fly2 = FlyweightFactory.getFlyweight("a");System.out.println(fly1==fly2);Flyweight fly3 = FlyweightFactory.getFlyweight("b");fly3.action(2);Flyweight fly4 = FlyweightFactory.getFlyweight("c");fly4.action(3);Flyweight fly5 = FlyweightFactory.getFlyweight("d");fly5.action(4);System.out.println(FlyweightFactory.getSize());}}

运行结果：

argument: 1
true
argument: 2
argument: 3
argument: 4
4