How do you aggregate the results of N parallel CompletableFutures?

The standard approach is CompletableFuture.allOf(cf1, cf2, ..., cfN), which returns a CompletableFuture<Void> that completes only once every one of the given futures has completed. You then chain a step to collect the individual results, typically written as allOf(futures.toArray(...)).thenApply(v -> futures.stream().map(CompletableFuture::join).collect(toList())); calling join() inside that step is safe because allOf already guarantees every future is done by that point, so join() will never actually block. If you instead only care about whichever future finishes first, CompletableFuture.anyOf(cf1, cf2, cf3) returns a CompletableFuture<Object> that completes as soon as any one of them does, which you then cast to the expected type. As of Java 21, structured concurrency offers a cleaner alternative for this same pattern: StructuredTaskScope.open(Joiner.allSuccessfulOrThrow()) handles the fork-and-join bookkeeping for you without manual join() and allOf() calls.