MyCacheMapForJava8.java

package pattern3;

import java.util.*;
import java.util.function.Supplier;

/**
 * Created by cattaka on 17/07/04.
 * <p>
 * Gist for https://twitter.com/Kory__3/status/882212409967919104
 */
public class MyCacheMapForJava8<K, V> {
    public static class VoteCacheByScores extends MyCacheMapForJava8<VoteScore, Set<VotePoint>> {
        public VoteCacheByScores() {
            super(HashSet::new);
        }
    }

    public static class UuidToPlayerVotesMap extends MyCacheMapForJava8<UUID, VoteCacheByScores> {
        public UuidToPlayerVotesMap(Supplier<VoteCacheByScores> supplier) {
            super(VoteCacheByScores::new);
        }
    }

    public static class VotePointVotesCache extends MyCacheMapForJava8<VotePoint, Set<Vote>> {
        public VotePointVotesCache() {
            super(HashSet::new);
        }
    }

    private Supplier<V> mSupplier;
    private Map<K, V> mMap;

    private MyCacheMapForJava8(Supplier<V> supplier) {
        mSupplier = supplier;
        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 = mSupplier.get();
            mMap.put(k, result);
        }
        return result;
    }

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

class VoteScore {
}

class VotePoint {
}

class Vote {
}