设计模式（享元模式）

public interface Flyweight {
    public void doAction();
}

public class FlyweightImpl implements Flyweight{

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

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();
    }
}

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());
    }
}

doAction
doAction
doAction
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