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浅谈JAVA设计模式之——享元模式(Flyweight)
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一、概述
运用共享技术有效地支持大量细粒度的对象。
二、适用性
当都具备下列情况时,使用Flyweight模式:
一个应用程序使用了大量的对象。
完全由于使用大量的对象,造成很大的存储开销。
对象的大多数状态都可变为外部状态。
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。
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。
三、参与者
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。
ConcreteFlyweight 实现Flyweight接口,并为内部状态(如果有的话)增加存储空间。ConcreteFlyweight对象必须是可共享的。它所存储的状态必须是内部的;即,它必须独立于ConcreteFlyweight对象的场景。
UnsharedConcreteFlyweight 并非所有的Flyweight子类都需要被共享。Flyweight接口使共享成为可能,但它并不强制共享。在Flyweight对象结构的某些层次,UnsharedConcreteFlyweight对象通常将ConcreteFlyweight对象作为子节点。
FlyweightFactory 创建并管理flyweight对象。确保合理地共享flyweight。当用户请求一个flyweight时,FlyweightFactory对象提供一个已创建的实例或者创建一个(如果不存在的话)。
四、类图
五、示例
Flyweight
package com.lyz.design.flyweight;
/**
* Flyweight
* @author binghe
*
*/
public interface Flyweight {
void action(int arg);
}
ConcreteFlyweight
package com.lyz.design.flyweight;
/**
* ConcreteFlyweight
* @author binghe
*
*/
public class FlyweightImpl implements Flyweight {
public void action(int arg) {
// TODO Auto-generated method stub
System.out.println("参数值: " + arg);
}
}
FlyweightFactory
package com.lyz.design.flyweight;
import java.util.HashMap;
import java.util.Map;
/**
* FlyweightFactory
* @author binghe
*
*/
public 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();
}
}
Test
package com.lyz.design.flyweight;
/**
* Test
* @author binghe
*/
public class Test {
public static void main(String[] args) {
// TODO Auto-generated method stub
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");
fly4.action(4);
System.out.println(FlyweightFactory.getSize());
}
}
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