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享元模式,通过共享对象的方式有效地支持大量细粒度的对象。
一、关键点
1)先看下这个模式点关键点:
对象池:该模式的最大特点就是实现对象的缓存,以避免对象的重复创建,从而达到提升性能和内存使用优化的目的;
状态外部化:为实现该模式,另外的一个特点就是状态外部化,以方便缓存对象的访问。
2)我们再来看下它的类图关系:
FlyweightFactory:享元工厂,管理享元对象池和创建享元对象;
Flyweight:享元对象的基类;
ConcreteFlyweight:具体的享元对象。
二、实现
2.1 Flyweight 享元对象基类
public abstract class Flyweight {
public abstract void operation();
}
2.2 ConcreteFlyweight 具体享元对象
public class ConcreteFlyweight extends Flyweight {
@Override
public void operation() {
/** do somethings of concrete */
}
}
2.3 FlyweightFactory 享元工厂
public class FlyweightFactory {
private static Map<String, Flyweight> sFlyweightMap = new ConcurrentHashMap<String, Flyweight>();
public static Flyweight getFlyweight(String type) {
if (sFlyweightMap.containsKey(type)) {
return sFlyweightMap.get(type);
} else {
Flyweight flyweight = new ConcreteFlyweight(type);
sFlyweightMap.put(type, flyweight);
return flyweight;
}
}
}
2.4 Client 客户端的对象
public class Client {
public static void main(String[] args) {
Flyweight flyweightA = FlyweightFactory.getFlyweight("A");
flyweightA.operation();
Flyweight flyweightB = FlyweightFactory.getFlyweight("B");
flyweightB.operation();
}
}
三、小结
3.1 对象池 该模式的目的与特点,通过map的形式缓存需要的对象,从而提升性能;
3.2 状态外部化 为了使用该模式,我们常常将状态外部化,这也直接增加了程序的复杂度。