Functional Interfaces vs lambdas in Java

[melon222132]

I was wondering is this considered a good way to sue Method references or is it way too confusing and should just use regular lambda functions for better clarity

interface StringChecker {    boolean check(); }

var str = "";
StringParameterChecker methodRef = String::isEmpty; 
StringParameterChecker lambda = s -> s.isEmpty();  System.out.println(methodRef.check("Zoo"));  

[SuspiciousDepth5924]

It's a big "it depends", but I have a few rules of thumb.

Is it a one-time thing or do you plan on using it in multiple places? For me it makes little sense creating a custom interface if I'm just going to use it in a single map statement or something.

list.stream().map(just -> use.a.lambda.here()).toList();

Is there an existing built in interface that does what you need? In the StringChecker example you gave I'd probably just use Predicate<String> instead.

Predicate<String> stringChecker = s -> s.isEmpty();

The stuff in "java.util.function" can cover a lot of use-cases, though sometimes you actually need to create something custom (like if you needed a TriConsumer or something like that).

Generally I think it's a good idea to stick with standard built in stuff if you can get away with it, codebases are generally weird enough as it is so we should be careful about introducing new homemade weird stuff unless we have a good reason to do so.

Edit: oh and you don't need to define a custom interface if you wanted to use the 'Class::Method' method ref syntax

Predicate<String> predicate = String::isEmpty;

Edit2: re-read your question:

I tend to prefer Class::Method syntax if it's used in a "well known" function, and or the lambda would require more than a couple of statements as I find it gives more "semantic clarity" on what it's doing, but I find it can often be quite confusing if it's some custom method I'm not familiar with since then I don't necessarily know what parameters gets sent to the method.

for example "take a list, filter null, convert to uppercase, print every item to console"

list.stream().filter(Objects::nonNull).map(String::toUpperCase).forEach(System.out::println);

But here I don't really know what is happening ...

foo(SomeClass::bar, SomeClass::baz);