MyCacheMap.java

package pattern2;

import java.util.*;

/**
 * Created by cattaka on 17/07/04.
 * <p>
 * Gist for https://twitter.com/Kory__3/status/882212409967919104
 */
public abstract class MyCacheMap<K, V> {
    public static class VoteCacheByScores extends MyCacheMap<VoteScore, Set<VotePoint>> {
        @Override
        Set<VotePoint> createNewSet() {
            return new HashSet<>();
        }
    }

    public static class UuidToPlayerVotesMap extends MyCacheMap<UUID, VoteCacheByScores> {
        @Override
        VoteCacheByScores createNewSet() {
            return new VoteCacheByScores();
        }
    }

    public static class VotePointVotesCache extends MyCacheMap<VotePoint, Set<Vote>> {
        @Override
        Set<Vote> createNewSet() {
            return new HashSet<>();
        }
    }

    private Map<K, V> mMap;

    private MyCacheMap() {
        mMap = new HashMap<>();
    }

    public V get(K k) {
        V result = mMap.get(k);
        if (result == null) {
            // NOTE: Java 8ならmMap.computeIfAbsent()が使える
            result = createNewSet();
            mMap.put(k, result);
        }
        return result;
    }

    abstract V createNewSet();

    // TODO: 必要に応じてMapのメソッドをdelegateする
}

class VoteScore {
}

class VotePoint {
}

class Vote {
}