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anyOf has to somehow tell you what was the result of the specific CompletableFuture whose completion triggered anyOf . That's not necessary in case of allOf because you know which futures completed -- all of them.

allOf (just as anyOf ) doesn't require that all futures bear the same type. So if it were to return a future of collection, it would have to be a collection of Object which is probably not what you want anyway.

If you really want to have allOf return a future of collection, it's fairly straightforward to write your own:

public static CompletableFuture<List<Object>> myAllOf(CompletableFuture<?>... futures) {
     return CompletableFuture.allOf(futures)
            .thenApply(x -> Arrays.stream(futures)
                    .map(f -> (Object) f.join())
                    .collect(toList())
If you have a type-safe version of this problem and need to convert a collection of futures of a certain type to a future of collection of that same type, see this question for several examples: List<Future> to Future<List> sequence
                Thanks for your explanation, but anyway I cant understand why allOf cant return stream of CompletableFuture or results or smth else...
– Everv0id
                Dec 4, 2015 at 12:36
This is similar to Misha's answer, but with a generic type:
public class Futures {
    public static <T> CompletableFuture<List<T>> all(List<CompletableFuture<T>> futures) {
        CompletableFuture<Void> cfv = CompletableFuture.allOf(futures.toArray(new CompletableFuture[0]));
        return cfv.thenApply(future -> {
            return futures.stream()
                    .map(completableFuture -> completableFuture.join())
                    .collect(Collectors.toList());
That's the method the Java API should provide.
        
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