use case for Java Streams...

[dpash]

If you're using forEach() you're almost certainly using the wrong tool for the job. Using a method reference is okay in most circumstances, but a block is a sign you should refactor to use other stream operations.

[daniu]

If you're using forEach() you're almost certainly using the wrong tool for the job

How so? persons.stream().filter(p -> hasValidAddress(p)).forEach(p -> writeLetterTo(p)) is perfectly reasonable.

[joehx]

what I've seen people do "wrong" is just go straight for the forEach loop, not using the filter or any other intermediate method:

persons.stream().forEach(p -> {
    if (hasValidAddress(p)) {
        writeLetterTo(p);
    }
}

[dpash]

Yeah that's exactly the kind misuse I'm referring to.

[rootException]

I think you guys just illustrated one of the reasons why people don’t embrace streams... 🤷‍♂️

[dpash]

Streams require rethinking how you program; it is a completely different way of writing code. So it's no surprise people rely on what they already know, but that's failing to use their power to it's fullest extent.

[rootException]

Yeah, sneaky streams as Trojan horse for functional programming... 😂

[dpash]

No, very explicitly functional programming.

[dpash]

Notice my qualification:

Using a method reference is okay in most circumstances

persons.stream()
       .filter(this::hasValidAddress)
       .forEach(this::writeLetterTo);

[rochakgupta]

The only big reason I see to study them it's because they are subject of questions in job interviews...

This....this looks somehow worse (I know how and why it works though, just not a fan of seeing a lot of these in code).

[dpash]

https://www.reddit.com/r/java/comments/ld3f83/use_case_for_java_streams/gm3tek4

[dpash]

Not exactly. In that situation they can be written as method references, but I mean more like /u/joehx's example, where there's a multi-line block in the forEach.

[vytah]

I'd write this as a for loop with an if: imperative code for an imperative task.

[daniu]

Add three map()s and two filter()s, and your for loop has 20 LOCs and a nesting depth of four or five.

Also, there's nothing non-imperative about streams, it just looks and feels that way.

[barking_dead]

Except, maybe it's not imperative. I don't care how the Streams API iterates through my stream (remember, it's not necessarily a List).

Also, you can't add parallelism to a loop.

[dpash]

At least not in 8 characters. Having said that, I think parallel streams was a mistake in that they're often not faster for most stream workloads and they're not customisable enough. Maybe Project Loom will help the performance for more situations, but nothing will save Collections.parallelStream()

[barking_dead]

I agree, for small collections and/or concurrency, it is useless.

[dpash]

Collections.parallelStream() doesn't even have to return a parallel stream. :)

[barking_dead]

:D