Java Map + lambda, the alternative forms of if-else

If your program has tons of if-eles like this, maybe you could try rewriting it as Map + Function. Function can be turned into lambda form to make it look more elegant. 😁

switch (type) {
    case RANK:
        searchRankBooks();
        break;
    case RECOMMENDATION:
        searchRecommendationBooks();
        break;
    default:
        new ArrayList<>();
        break;
}

Create a Map<String, Function<K, V>> in your service, use it to store if-else business functions.

private Map<String, Function<TYPE, List<String>>> bookSearchTypeMap = new HashMap<>();

Init a Function as value, Function can be written as the lambda, like this👇

bookSearchTypeMap.put(RANK.name(), type -> bookTypeService.rank(type));

use a getResult(K) to get results.

public List<String> getResult(TYPE type) {
    Function<TYPE, List<String>> result = bookSearchTypeMap.get(type.name());
    if (result != null) {
        return result.apply(type);
    }
    return new ArrayList<>();
}

Called it in the Controller.

public List<String> books(TYPE type){
    return queryBookService.getResult(type);
}

Log:

> Task :Main.main()
rank[Corpus Delicti, Die Insel der Tausend Leuchttürme, Dark Mirror Castle, Iron Flame – Flammengeküsst]
recommendation[Die Insel der Tausend Leuchttürme, Vergissmeinnicht - Was bisher verloren war, Dark Shadow Castle, Fighting Fate]

Here is just one way to implement it, you can rewrite it a bit to use it in any framework.

Happy Coding!

Full Demo👨‍💻

public class QueryBookService {
    private BookTypeService bookTypeService = new BookTypeService();
    private Map<String, Function<TYPE, List<String>>> bookSearchTypeMap = new HashMap<>();

    public QueryBookService() {
        bookSearchTypeMap.put(RANK.name(), type -> bookTypeService.rank(type));
        bookSearchTypeMap.put(RECOMMENDATION.name(), type -> bookTypeService.recommendation(type));
    }

    public List<String> getResult(TYPE type) {
        Function<TYPE, List<String>> result = bookSearchTypeMap.get(type.name());
        if (result != null) {
            return result.apply(type);
        }
        return new ArrayList<>();
    }
}

public class BookTypeService {
    public List<String> rank(TYPE type){
        return getRank(type);
    }

    public List<String> recommendation(TYPE type){
        return getRecommendation(type);
    }
}

public class BookSearchController {
    private QueryBookService queryBookService = new QueryBookService();

    public List<String> books(TYPE type){
        return queryBookService.getResult(type);
    }
}

public enum TYPE {
    RANK, RECOMMENDATION
}

// Mocks
public class BookMocks {
    public static List<String> getRank(TYPE type) {
        List<String> list = new ArrayList<>();
        list.add("Corpus Delicti");
        list.add("Die Insel der Tausend Leuchttürme");
        list.add("Dark Mirror Castle");
        list.add("Iron Flame – Flammengeküsst");
        return list;
    }

    public static List<String> getRecommendation(TYPE type) {
        List<String> list = new ArrayList<>();
        list.add("Die Insel der Tausend Leuchttürme");
        list.add("Vergissmeinnicht - Was bisher verloren war");
        list.add("Dark Shadow Castle");
        list.add("Fighting Fate");
        return list;
    }
}

public class Main {
    public static void main(String[] args) {
        BookSearchController controller = new BookSearchController();

        System.out.println("rank" + controller.books(RANK));
        System.out.println("recommendation" + controller.books(RECOMMENDATION));

    }
}