Optional has more syntactic sugar for more complex scenarios / functional call chaining that prevents repetitive if checks

Optional.ofNullable(myObj)
  .map(MyClass::getProperty)
  .map(MyOtherClass::getAnotherProperty)
  .filter(obj -> somePredicate(obj))
  .orElse(null)

This is completely null safe, the function calls are only made if the object is not null

I had never heard of Phaser, but it looks pretty cool. I just read Baeldung's Guide to Phaser and correct me if I'm wrong, but doesn't it kind of seem like a race condition (it could just be how they use it in the examples)?

class LongRunningAction implements Runnable {
    private String threadName;
    private Phaser ph;

    LongRunningAction(String threadName, Phaser ph) {
        this.threadName = threadName;
        this.ph = ph;
        ph.register();
    }

    @Override
    public void run() {
        ph.arriveAndAwaitAdvance();
        try {
            Thread.sleep(20);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        ph.arriveAndDeregister();
    }
}

then

executorService.submit(new LongRunningAction("thread-1", ph));
executorService.submit(new LongRunningAction("thread-2", ph));
executorService.submit(new LongRunningAction("thread-3", ph));

if ph.arriveAndAwaitAdvance(); is called before all of the LongRunningActions are initialized, won't it proceed before it is supposed to?

Write tests. Not too many. Mostly integration.

assuming you propose the idea to migrate to kotlin, it would go something like this:

• talk to your other developers and see if they feel the same way. get other developer buy-in
• propose the idea to management with reasons why it would be beneficial
• management now either buys in and approves kotlin usage, or says it's not worth it

if management says yes, you now have like 20 people who have vetted and agreed with the idea. once you start writing Kotlin it's not like EVERYTHING is all of the sudden Kotlin. it's an iterative process, and hopefully you have test coverage. you can even re-use your existing java tests since the languages are interoperable. Assuming you follow a normal development process, the odds of a catastrophic bug coming out of nowhere to cause millions of dollars of losses wouldn't even cross my mind.

that being said, assuming the current code works decently well, management will have no motivation or reason to approve a total rewrite in a new language. it's more likely that they will only approve starting to trickle in kotlin for new projects or features, which even further reduces the likelihood of a catastrophic bug happening.

the developers don't have to of left the team to make it legacy code

I think generally it’s preferably to work in the affirmative, i.e. bar == null? but I’ll admit I don’t stick to this 100% of the time and generally just use whatever feels better / more appropriate in the moment

what about after the HUP? The time between HUP and the new binary starting up would be considered downtime

basically anything besides Alibaba or Oracle you probably won’t notice a difference. at work I use corretto since we deploy on aws, at home I either use Temurin or Corretto. One thing benefit of Corretto is they do tend to backport some patches to older versions if you aren’t able to use the latest yet. https://whichjdk.com/