关于CompletableFuture.anyOf方法文档表述的技术咨询

Let’s break down exactly what that phrase refers to in plain terms:

• The "same result" is the outcome—either a successful return value or a thrown exception—of the first CompletableFuture in your input array that finishes executing. This applies whether the future completes normally or hits an error.
• It doesn’t matter which position the future occupies in the cfs parameter; the moment any of them finishes, the new CompletableFuture returned by anyOf() immediately adopts that future’s result.

Example to Make It Concrete #

Suppose you spin up three asynchronous tasks with different wait times:

CompletableFuture<String> future1 = CompletableFuture.supplyAsync(() -> {
    try { Thread.sleep(3000); } catch (InterruptedException e) {}
    return "Result from slow Future 1";
});

CompletableFuture<Integer> future2 = CompletableFuture.supplyAsync(() -> {
    try { Thread.sleep(1000); } catch (InterruptedException e) {}
    return 42;
});

CompletableFuture<Boolean> future3 = CompletableFuture.supplyAsync(() -> {
    try { Thread.sleep(2000); } catch (InterruptedException e) {}
    return true;
});

CompletableFuture<Object> combinedFuture = CompletableFuture.anyOf(future1, future2, future3);

In this scenario, future2 finishes first after 1 second. So combinedFuture will complete with the value 42—exactly the result of the first completed input future.

Edge Case: Exceptional Completion #

If the first completed future throws an exception, the combined future will also complete exceptionally with that same error. For example:

CompletableFuture<String> failingFuture = CompletableFuture.supplyAsync(() -> {
    throw new RuntimeException("Oops, failed right away!");
});

CompletableFuture<String> slowFuture = CompletableFuture.supplyAsync(() -> {
    try { Thread.sleep(5000); } catch (InterruptedException e) {}
    return "Late, successful result";
});

CompletableFuture<Object> combined = CompletableFuture.anyOf(failingFuture, slowFuture);

Here, failingFuture completes immediately with an exception, so combined will hold that RuntimeException as its result—completely ignoring the slow, successful future that finishes later.

内容的提问来源于stack exchange，提问作者Venkatesh Laguduva