> but it requires knowing what class and value to pass

Unless you use a text editor without any coding capabilities, your IDE should show you which values you can pass. The alternative is to have more methods, I guess?

> why can't I just pass 20 or 20_000 or something

20 what? Milliseconds? Seconds? Minutes? While I wouldn't write the full Duration.ofSeconds(20) (you can save the "Duration."), I don't understand how one could prefer a version that makes you guess the unit.

> proxy(ProxySelector.of(new InetSocketAddress("proxy.example.com", 80))), geez that's complex

Yes it is, can't add anything here. There's a tradeoff between "do the simple thing" and "make all things possible", and Java chooses the second here.

> .authenticator(Authenticator.getDefault()), why not just pass bearer token or something?

Because this Authenticator is meant for prompting a user interactively. I concur that this is very confusing, but if you want a Bearer token, just set the header.

Fair points.

> Unless you use a text editor without any coding capabilities, your IDE should show you which values you can pass. The alternative is to have more methods, I guess?

Fair enough, as much as I don't like it, in Java world it's safe to assume everyone is using an IDE. And when your language is (essentially) dependent on an IDE, this becomes a non-issue (actually I might argue it's even a nice feature since it's very type safe).

> 20 what? Milliseconds? Seconds? Minutes? While I wouldn't write the full Duration.ofSeconds(20) (you can save the "Duration."), I don't understand how one could prefer a version that makes you guess the unit.

I would assume milliseconds and would probably have it in the method name, like timeoutMs(...) or something. I will say it's very readable, but if I was writing it I'd find it annoying. But optimizing for readability is a reasonable decision, especially since 80% of coding is reading rather than writing (on average).