Java tutorial
import java.util.Arrays; import java.util.IntSummaryStatistics; import java.util.List; import java.util.stream.Collectors; public class Main { public static void main(String[] args) throws Exception { List<Person> persons = Arrays.asList(new Person("Max", 18), new Person("Peter", 23), new Person("Pamela", 23), new Person("David", 12)); IntSummaryStatistics ageSummary = persons.stream().collect(Collectors.summarizingInt(p -> p.age)); System.out.println(ageSummary); } } class Person { String name; int age; Person(String name, int age) { this.name = name; this.age = age; } @Override public String toString() { return name; } }