Using Map/Dictionary as an alternative to switch case

Question

At the risk of this being an opinion based question, would creating a Map/dictionary where the keys are predicates and the values the action to be made be a good and viable substitute for switch case?

For example (following Java Map) :

    Map.of(predicate1, action1, ... predicateN, actionN)
    .entrySet().stream()
    .filter(e -> e.getKey()).findAny()
    .ifPresentOrElseThrow().getValue();

Answer 1

It's an interesting approach, I sometimes do it for filters or mappers. The only thing I would change would be to avoid using a Map if you don't really need one (what would be the hashcode of your Predicate - it can be looked up, but still, it's not super straightforward).

Instead, you can put the Predicate and the Consumer in some sort of Pair<> or Tuple<>, or even create your own structure:

record PossibleAction<T>(
        Predicate<T> predicate,
        Consumer<T> action
) {
    // if you use a custom structure you can define these methods
    // and use .appliesFor(data) instead of using .getPredicate().test(data)
    public boolean appliesFor(T data) {
        return predicate.test(data);
    }

    public void apply(T data) {
        action.accept(data);
    }
}

Now you can have a list of these PossibleActions:

List<PossibleAction<String>> actions = List.of(
    new PossibleAction<>(s -> s.contains("A"), s -> System.out.println("1") ),
    new PossibleAction<>(s -> s.contains("B"), s -> System.out.println("2") ),
    new PossibleAction<>(s -> s.contains("C"), s -> System.out.println("3") )
);

And you can use this, as pointed out by you in the initial post:

void performActions(String data) {
    actions.stream()
            .filter(a -> a.appliesFor(data))
            .forEach(a -> a.apply(data));
}