A completable future is something that in the future may complete. I think that's self explanatory. A promise seems equally vague.

Boilerplate looks the same. JS is just a function, Java they put a class around it. Java requires exception handling which is annoying but having fought errors in async JS, I'll take all I can get.

API is eh. Sure. But that's not even shown in this example so I have no idea.

So JS saves like 3 lines? Is that really so much better?

It’s probably intentional, because it allows showing the Java 1 Thread approach succinctly.

But as long-term Java person, I find it jarring.

It's a little tiring to read a Java example with an entry-point (the public-static-void bit) and then a JavaScript example without one.

If you strip that out the original Java is:

  var future = CompletableFuture.supplyAsync(() -> {
        try {
                Thread.sleep(10000);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
            return "Data Fetched";
        });
  future.thenAccept(result -> System.out.println(result));
  System.out.println("Prints first"); // prints before the async result

Arguably it's still a different thing you're doing, because it's not scheduling a task on a pool, it's creating a thread which sleeps for 10 seconds.

Or as a node successfully been able to start utilizing more cores underneath its JavaScript single thread model. It presents the programmer?

I just remember early node.js from like 15 years ago and the single background task limitation of JavaScript running in a web page.

Cuz you got async code is nice, but what you really wanted to be able to harness in modern CPUs is multi-core

That said, I've been looking for an article like this for a while, although I think there are other associated libraries that also had steps in here. I do think the jvm adopted a lot of those, but I'm not sure if they actually are better than the original extension libraries.

  void main() {
      CompletableFuture<String> future = CompletableFuture.supplyAsync(this::asyncMethod);
      future.thenAccept(result -> IO.println(result));
      IO.println("Prints first");             // prints before the async result
      future.join();                          // Wait for future to complete
  }

  String asyncMethod() {
      try {
          Thread.sleep(10000);
      } catch (InterruptedException e) {
          return "Interrupted";
      }
      return "Data Fetched";
  }

1. Move the asynchronous function called in the CompletableFuture to its own method

2. Use Java 25 "instance main method" (see JEP 25: https://openjdk.org/jeps/512)

3. Use Java 25 IO.println() to simplify console output

4. Instead of throwing a fatal exception on interruption, return "Interrupted" immediately.

5. Use future.join() so the main method waits for the future to complete and the "Data fetched" output is printed.

This program can be run directly from source with `java Example.java`. (If you're using Java 24 or a version of Java 25 prior to EA 22, you need to use `java --enable-preview Example.java`)

Here is a modified version of the example that interrupts the thread:

  void main() {
      ExecutorService executor = Executors.newSingleThreadExecutor();
      CompletableFuture<String> future = CompletableFuture.supplyAsync(this::asyncMethod, executor);
      future.thenAccept(result -> IO.println(result));
      IO.println("Prints first");             // prints before the async result
      executor.shutdownNow();
      future.join();                          // Wait for future to complete
  }

  String asyncMethod() {
      try {
          Thread.sleep(10000);
      } catch (InterruptedException e) {
          return "Interrrupted";
      }
      return "Data Fetched";
  }