Sub Type Comparator One Liner Issue

Question

Why do I need a temporary variable as personAgentComparator needed here and to call reversed() on that?

public class SubTypeComparatorIssue {

  public void sortAgeFromOldToYoung(List<Person> persons) {
    //persons.sort(Comparator.comparing(person -> person.age).reversed());
      Comparator<Person> personAgeComparator = Comparator.comparing(person -> person.age);
      persons.sort(personAgeComparator.reversed());
  }
}

class Person {
  int age;
}

How do I get the sorting and reversing to with the comparator as a one-liner? I am getting an error in the lambda expression under person.age when currying the reversed() on that commented line. If the reversed() is not added, I don't get that error even! Hence did for now in two lines with that temporary personAgentComparator and called reversed() on it while calling the sort().

Basically, how do I get a oneliner to do this whole operation?

I expect a correction on this line to have it as a oneliner to get the persons list reverse sorted by person's age.

persons.sort(Comparator.comparing(person -> person.age).reversed());

Answer 1

One of the way using lambda

persons.sort((p1, p2) -> Integer.compare(p2.age, p1.age));