java streams: Collect stream of Iterable

Question

I'm getting a compilation error on:

@Override
public Map<String, T> loadAll(Iterable<? extends String> keys) {
    return Stream.of(keys)
      .collect(Collectors.toMap(Function.identity(), this::load));
}

The compiler message is:

The method collect(Collector<? super Iterable<capture#1-of ? extends String>,A,R>) in the type Stream<Iterable<capture#1-of ? extends String>> is not applicable for the arguments (Collector<String,capture#2-of ?,Map<Object,Reference>>)

Any work around?

what do you think `Stream.of(keys)` returns? – Eugene Feb 10 '19 at 18:24 — Eugene, Feb 10 '19 at 18:24
what are you trying to achieve, can you elaborate? – Naman Feb 10 '19 at 18:26 — Naman, Feb 10 '19 at 18:26

score 3 · Accepted Answer · answered Feb 10 '19 at 18:23

3

It seems that you think that Stream.of(keys) will create a Stream<String>, but that is not the case. To create a Stream from an Iterable, you should use StreamSupport#stream:

public Map<String, T> loadAll(Iterable<? extends String> keys) {
    return StreamSupport.stream(keys.spliterator(), false)
                        .collect(Collectors.toMap(Function.identity(), this::load));
}

This assumes that your load method returns T.

answered Feb 10 '19 at 18:23

Jacob G.

28,856
5
62
116

Is there any jdk 11 more elegant way to achieve the same? – Jordi Feb 11 '19 at 08:56

java streams: Collect stream of Iterable

1 Answers1