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CompletableFuture<String> future = CompletableFuture.supplyAsync(() -> {
			System.out.println("Hello: " + Thread.currentThread().getName());
			return "Hello";
		}).thenApplyAsync((s) -> {
			System.out.println(Thread.currentThread().getName());
			return s.toUpperCase();
		});

/*
Hello: ForkJoinPool.commonPool-worker-1
ForkJoinPool.commonPool-worker-2
*/
// thenApply() 일 경우 두개의 스레드가 같음


CompletableFuture<String> future = CompletableFuture.supplyAsync(() -> {
	System.out.println("Hello: " + Thread.currentThread().getName());
	return "Hello";
});
CompletableFuture<String> future2 = CompletableFuture.supplyAsync(() -> {
	System.out.println("World: " + Thread.currentThread().getName());
	return "World";
});
List<CompletableFuture<String>> futures = List.of(future, future2);
CompletableFuture[] futureArray = futures.toArray(new CompletableFuture[futures.size()]);

// thenApply에서의 v는 의미 없는 값임
// allOf 메서드가 실행되고 난 뒤, 새로운 CompletableFuture가 반환되는데,
// 이 CompletableFuture의 반환값이라 보면됨(의미x)
CompletableFuture<List<String>> list = CompletableFuture.allOf(futureArray)
	.thenApply((v) -> futures.stream().map(CompletableFuture::join).collect(Collectors.toList()));

list.get().forEach(System.out::println);
// System.out.println(future.get());