Using Java Predicate and Lambda

Question

Why does the below code return Predicate<String> and not boolean?

My understanding is that the !s.isEmpty() check here is going against the Predicate boolean test(T t); The return type here is boolean.

So in my lambda should my nonEmptyStringPredicate not be of type boolean? Obviously, it's not, I'm just trying to understand why it's not.

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

Answer 1

If you really are willing to get a boolean though from the Predicate, you can use its test method:

Predicate<String> nonEmptyStringPredicate = s -> !s.isEmpty();
boolean val = nonEmptyStringPredicate.test("any"); // true

Predicate on the other hand is just a FunctionalInterface, that you've represented using a lambda expression.