How to get my object (Generator) from a Map<UUID, List<Generator>> with streams?

Question

I've been wanting to check the location of my Generator and use streams to check if the location is valid.

The idea was as follows;

public Generator getGeneratorFromLocation(final Location location) {
        for (List<Generator> generator : playerGeneratorMap.values()) {
            for (Generator generator1 : generator) {
                if (generator1.getGenLocation().equals(location)) {
                    return generator1;
                }
            }
        }
        return null;
    }

I'm wanting to return a Generator from this using streams instead to try and learn more ways of doing it.

Current map:

public final Map<UUID, List<Generator>> playerGeneratorMap = new HashMap<>();

Any help would be greatly appreciated.

Answer 1

You can use AtomicRef object to init a retVal and then assign the wanted Generator to it in the lambda expression because regular vars can't be assigned in lambdas, only final or effectivly final can be used inside arrow functions.

This function should solve the problem :)

public Generator getGeneratorFromLocation(final Location location) {

    AtomicReference<Generator> retVal = new AtomicReference<>(null);

    playerGeneratorMap.values().stream().forEach(generators -> {
        generators.forEach(generator -> {
            if (generator.getLocation().equals(location)) {
                retVal.set(generator);
            }
        });
    });

    return retVal.get();
}

By the way, streams are unnecessary because you have Collection.forEach instead of Stream.forEach, streams are used for more 'exotic' types of iterations like, filter, anyMatch, allMatch, reduce and such functionalities, you can read about Streams API on Oracle's website, I'll link in the docs for you for future usage, important for functional proggraming.