In this example we can see record Person and we use stream’s sorted(Comparator<? super T> comparator) method to sort the List of people by their age. So sorted(Comparator<? super T> comparator) accept as parameter Comparator. For this reason we have to create Comparator and we sort inside by age.
The documentation for sorted(Comparator<? super T> comparator) state:
Returns a stream consisting of the elements of this stream, sorted according to the provided Comparator.
For ordered streams, the sort is stable. For unordered streams, no stability guarantees are made.
This is a stateful intermediate operation.
import java.util.Comparator;
import java.util.List;
import java.util.stream.Collectors;
public class MainClassTest {
record Person (String name, Integer age) {}
public static void main(String[] args)
{
List<Person> people = List.of(
new Person("Jim", 56),
new Person("Tom", 13),
new Person("Maria", 20)
);
Comparator<Person> ageComparator = (p1, p2) -> p1.age().compareTo(p2.age);
// Sort by natural order
List<Person> sortedPeopleList = people
.stream()
.sorted(ageComparator)
.collect(Collectors.toList());
// get the youngest person
System.out.println("Youngest person: " + sortedPeopleList.get(0));
// get the oldest person
Integer lastIndex = sortedPeopleList.size() - 1;
System.out.println("Oldest person: " + sortedPeopleList.get(lastIndex));
}
}
Output:
Youngest person: Person[name=Tom, age=13]
Oldest person: Person[name=Jim, age=56]