Retrieving a List from a Java.Util.Stream.Stream in Java 8

Retrieving a List from a java.util.stream.Stream in Java 8

What you are doing may be the simplest way, provided your stream stays sequential—otherwise you will have to put a call to sequential() before forEach.

[later edit: the reason the call to sequential() is necessary is that the code as it stands (forEach(targetLongList::add)) would be racy if the stream was parallel. Even then, it will not achieve the effect intended, as forEach is explicitly nondeterministic—even in a sequential stream the order of element processing is not guaranteed. You would have to use forEachOrdered to ensure correct ordering. The intention of the Stream API designers is that you will use collector in this situation, as below.]

An alternative is

targetLongList = sourceLongList.stream()
    .filter(l -> l > 100)
    .collect(Collectors.toList());

java 8 streams copy specific objects from map to list

Figured out a possible solution myself:

return Stream.of(fruitNames)
             .map(fruitMap::get)
             .filter(Objects::nonNull)
             .collect(Collectors.toList());

Get item from first list of list inside list - java 8

Conceptually this can be reframed as trying to get the "greatest" BankConversionFees, where "greatest" means the one containing the single greatest individual rate.

This can be represented in a simple, straightforward manner using Stream.max(Comparator) with a comparator that compares the BankConversionFees based on the largest rate (treating any empty fee history lists as smaller than any non-emtpy ones):

Comparator<BankConversionFees> comparator = Comparator.comparing(
        f -> f.getFeesHistory().stream().map(FeesHistory::getRate).max(Comparator.naturalOrder()),
        Comparator.nullsFirst(Comparator.comparing(o -> o.orElse(null))));

return allFees.stream().max(comparator);

If you want to continue to return an empty optional in the case where no BankConversionFees has any rates, as opposed to returning one of the fees without rates, you can filter accordingly:

Comparator<BankConversionFees> comparator = Comparator.comparing(
        h -> h.getFeesHistory().stream().map(FeesHistory::getRate).max(Comparator.naturalOrder()).orElseThrow());

return allFees.stream().filter(f-> !f.getFeesHistory().isEmpty()).max(comparator);

How can I get a List from some class properties with Java 8 Stream?

You can use map :

List<String> names = 
    personList.stream()
              .map(Person::getName)
              .collect(Collectors.toList());

EDIT :

In order to combine the Lists of friend names, you need to use flatMap :

List<String> friendNames = 
    personList.stream()
              .flatMap(e->e.getFriends().stream())
              .collect(Collectors.toList());

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