Converting to streams

Question

I'd like to convert the following code, which breaks from the outer loop, into Java 8 Streams.

private CPBTuple getTuple(Collection<ConsignmentAlert>  alertsOnCpdDay)
{
    CPBTuple cpbTuple=null;

    OUTER:
    for (ConsignmentAlert consignmentAlert : alertsOnCpdDay) {
        List<AlertAction> alertActions = consignmentAlert.getAlertActions();
        for (AlertAction alertAction : alertActions) {
            cpbTuple = handleAlertAction(reportDTO, consignmentId, alertAction);
            if (cpbTuple.isPresent()) {
                break OUTER;
            }
        }
    }
    return cpbTuple;
}

Answer 1

Every answer here uses flatMap, which until java-10 is not lazy. In your case that would mean that alertActions is traversed entirely, while in the for loop example - not. Here is a simplified example:

static class User {
    private final List<String> nickNames;

    public User(List<String> nickNames) {
        this.nickNames = nickNames;
    }

    public List<String> getNickNames() {
        return nickNames;
    }
}

And some usage:

public static void main(String[] args) {
    Arrays.asList(new User(Arrays.asList("one", "uno")))
            .stream()
            .flatMap(x -> x.getNickNames().stream())
            .peek(System.out::println)
            .filter(x -> x.equalsIgnoreCase("one"))
            .findFirst()
            .get();
}

In java-8 this will print both one and uno, since flatMap is not lazy.

On the other hand in java-10 this will print one - and this is what you care about if you want to have your example translated to stream-based 1 to 1.