Predicate.not

Definition

Predicate.not (Java 11) reverses a condition so you can use it with a method reference, for example filter(Predicate.not(String::isBlank)) instead of writing a lambda with !.

Example code

Keeping only the non-blank lines

import java.util.List;
import java.util.function.Predicate;

class Demo {
    public static void main(String[] args) {
        List<String> lines = List.of("first", "  ", "second", "");

        List<String> filled = lines.stream()
                .filter(Predicate.not(String::isBlank))       // reads like plain English
                .toList();

        System.out.println(filled);
    }
}

// Output:
// [first, second]