[BAEL-2932] Using Predicate.not to negate a method reference

core-java-modules/core-java-11/src/main/java/com/baeldung/predicate/not/FindPeople.java

@@ -0,0 +1,31 @@
+package com.baeldung.predicate.not;
+
+import java.util.List;
+import java.util.function.Predicate;
+import java.util.stream.Collectors;
+
+public class FindPeople {
+    public static void main(String[] args) {
+        List<Person> people = List.of(
+          new Person(1),
+          new Person(18),
+          new Person(2)
+        );
+
+        people.stream()
+          .filter(Person::isAdult)
+          .collect(Collectors.toList());
+
+        people.stream()
+          .filter(person -> !person.isAdult())
+          .collect(Collectors.toList());
+
+        people.stream()
+          .filter(Person::isNotAdult)
+          .collect(Collectors.toList());
+
+        people.stream()
+          .filter(Predicate.not(Person::isAdult))
+          .collect(Collectors.toList());
+    }
+}

core-java-modules/core-java-11/src/main/java/com/baeldung/predicate/not/Person.java

@@ -0,0 +1,19 @@
+package com.baeldung.predicate.not;
+
+public class Person {
+    private static final int ADULT_AGE = 18;
+
+    private int age;
+
+    public Person(int age) {
+        this.age = age;
+    }
+
+    public boolean isAdult() {
+        return age >= ADULT_AGE;
+    }
+
+    public boolean isNotAdult() {
+        return !isAdult();
+    }
+}