设计模式（享元模式）

享元模式可以理解是一个对象的缓存，通过构建一个享元工厂对所有的对象进行管理。

代码如下：

• Flyweight 享元的接口

public interface Flyweight {
    public void doAction();
}

• FlyweightImpl 具体被共享的类实现

public class FlyweightImpl implements Flyweight{

    @Override
    public void doAction() {
        System.out.println("doAction");
    }
}

• FlyweightFactory 享元工厂

public class FlyweightFactory {

    private static Map<String, Flyweight> flyweights 
        = new HashMap<String, Flyweight>();

    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();
    }
}

• APP 测试类

public class App {

    public static void main(String[] args) {
        FlyweightFactory factory = new FlyweightFactory();
        factory.getFlyweight("a").doAction();
        factory.getFlyweight("b").doAction();
        factory.getFlyweight("a").doAction();
        
        System.out.println(factory.getSize());
    }
}

• 输出结果

doAction
doAction
doAction
2