이미 생성한 객체가 있으면 공유, 없으면 생성하여 메모리 절약.

public interface Flyweight {
    String getData();
}

public class ConcreteFlyweight implements Flyweight {
    private String data;

    public ConcreteFlyweight(String data) {
        this.data = data;
    }

    public String getData() {
        return data;
    }
}

public enum FlyweightFactory {
    INSTANCE; // Singleton

    private Map<String, Flyweight> pool = new ConcurrentHashMap<>();

    public Flyweight getFlyweight(String key) {
        if(!pool.containsKey(key)) {
            pool.put(key, new ConcreteFlyweight(key));
        }

        return pool.get(key);
    }
}