Java Streams - replace nested for loops with Streams and return value

Question

I wonder how to replace this old school for loops with Java Streams:

public Long getStoreid(){
    for (PointDto point : tw.getPath().getPoints())) {
        for (PointOperationDto operation : point.getOperations()) {
            if (operation.isIncluded() {
                return point.getStoreId();
            }
        }
    }
}

I need to get storeId in the best possible way.\

UPDATE

After your answers the working version is:

tw.getPath().getPoints().stream()
                .filter(point -> point.getOperations().stream().anyMatch(PointOperation::isIncluded))
                .map(point::getStoreId)
                .findFirst()
                .orElse(null);

but now the question is how to use eg. Optional.ofNullable() to prevent NPE error because tw.getPath() can be null

Dmitrii B · Accepted Answer · 2021-02-14 16:12:01Z

2

I think you need that:

tw.getPath().getPoints().stream()
        .filter(point -> point.getOperations().stream().anyMatch(Operation::isIncluded))
        .map(Point::getStoreId)
        .findFirst()
        .orElse(0L);

edited Feb 14, 2021 at 16:12

answered Feb 14, 2021 at 14:49

Dmitrii B

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6 Comments

Domenico Sibilio Over a year ago

findFirst() might better translate the current implementation by OP.

Matexon Over a year ago

YES! That is what I was looking for - I have to use anyMatch()... Thank you

Matexon Over a year ago

@Dmitrii Bykov One more question - how to use Optional.ofNullable to prevent NPE error? tw.getPath() can be NULL... I tried with Optional.ofNullable(tw.getPath() but actually I don't have idea how to use it in this case

Dmitrii B Over a year ago

Optional.ofNullable(tw.getPath()).orElseGet(Collections.emptyList()).getPoints().stream() i think you need it

Dmitrii B Over a year ago

when you will use orElseGet() you should return Long or null, that's right. You also can use orElseThrow() and throw an exception. I don't know your logic. What do you want to return null or anyLong or throw exception...

|

Nowhere Man · Accepted Answer · 2021-02-14 15:04:54Z

2

The following operations are needed: map, filter, and findFirst:

public Long getStoreid() {
    return tw.getPath().getPoints().stream()
            .filter(Objects::isNonNull) // optional filter to prevent NPE
            .map(point -> point.getOperations().stream()
                .filter(Objects::isNonNull) // optional filter to prevent NPE
                .filter(PointOperationDto::isIncluded)
                .findFirst()
                .map(op -> point.getStoreId())
            )
            .findFirst()
            .orElse(null);
}

answered Feb 14, 2021 at 15:04

Nowhere Man

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