JAVA 设计模式 享元模式
用途
享元模式 (Flyweight)
运用共享技术有效地支持大量细粒度的对象。
享元模式是一种结构型模式。
结构
图-享元模式结构图
Flyweight : 它是所有具体享元类的超类或接口，通过这个接口，Flyweight 可以接受并作用于外部状态。
abstract class Flyweight {
public abstract void Operation(int extrinsicstates);
}ConcreteFlyweight : 是继承 Flyweight 超类或实现 Flyweight 接口，并为内部状态增加存储空间。
class ConcreteFlyweight extends Flyweight {
@Override
public void Operation(int extrinsicstates) {
System.out.println("共享的Flyweight : " + extrinsicstates);
}
}UnsharedConcreteFlyweight : 指那些不需要共享的 Flyweight 子类，因为 Flyweight 接口共享成为可能，但它并不强制共享。
class UnsharedConcreteFlyweight extends Flyweight {
@Override
public void Operation(int extrinsicstates) {
System.out.println("不共享的Flyweight : " + extrinsicstates);
}
}FlywightFactory :是一个享元工厂，用来创建并管理 Flyweight 对象。它主要是用来确保合理地共享 Flyweight ，当用户请求一个 Flyweight 时， FlyweightFactory 对象提供一个已创建的实例或创建一个（如果对象不存在的话）。
class FlywightFactory {
private Hashtable<String, Flyweight> flyweights = new Hashtable<String, Flyweight>();
public FlywightFactory() {
flyweights.put("X", new ConcreteFlyweight());
flyweights.put("Y", new ConcreteFlyweight());
flyweights.put("Z", new ConcreteFlyweight());
}
public Flyweight GetFlyweight(String key) {
return ((Flyweight)flyweights.get(key));
}
}测试代码
public class FlyweightPattern {
public static void main(String[] args) {
int extrinsicstates = 1;
FlywightFactory factory = new FlywightFactory();
Flyweight fx = factory.GetFlyweight("X");
fx.Operation(extrinsicstates);
Flyweight fy = factory.GetFlyweight("Y");
fy.Operation(++extrinsicstates);
Flyweight fz = factory.GetFlyweight("Z");
fz.Operation(++extrinsicstates);
Flyweight uf = new UnsharedConcreteFlyweight();
uf.Operation(++extrinsicstates);
}
}运行结果
共享的Flyweight : 1
共享的Flyweight : 2
共享的Flyweight : 3
不共享的Flyweight : 4推荐
本文属于 JAVA设计模式系列 。
参考资料
《大话设计模式》《HeadFirst设计模式》
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