allOf and anyOf

Definition

allOf waits until every future in a group is done, which is how you run many calls in parallel and then collect them. anyOf finishes as soon as the first one finishes.

Example code

Run several calls in parallel and gather the results

import java.util.List;
import java.util.concurrent.CompletableFuture;

class Demo {
    static CompletableFuture<String> call(String service, int millis) {
        return CompletableFuture.supplyAsync(() -> {
            try { Thread.sleep(millis); } catch (InterruptedException ignored) { }
            return service;
        });
    }

    public static void main(String[] args) {
        List<CompletableFuture<String>> calls = List.of(call("users", 150), call("orders", 100), call("prices", 50));

        CompletableFuture.allOf(calls.toArray(new CompletableFuture[0])).join();   // wait for all three
        System.out.println(calls.stream().map(CompletableFuture::join).toList());

        Object fastest = CompletableFuture.anyOf(call("slow", 300), call("fast", 20)).join();   // first one wins
        System.out.println(fastest);
    }
}

// Output:
// [users, orders, prices]
// fast