Java ListとIntStream

import java.util.ArrayList;
import java.util.List;

public class IntStreamTest1 {

    public static void main(String[] args) {

        List<Person> people = new ArrayList<>();
        people.add(new Person("Alice", 30));
        people.add(new Person("Bob", 19));
        people.add(new Person("Ronald", 40));
        people.add(new Person("Jimi", 27));
        people.add(new Person("Suzan", 60));
        people.add(new Person("Jeff", 80));
        people.add(new Person("Maria", 52));

        // min
        int min = people.stream().mapToInt(p -> p.getAge()).min().orElse(0);
        System.out.println(min);
        // 19

        // max
        int max = people.stream().mapToInt(p -> p.getAge()).max().orElse(0);
        System.out.println(max);
        // 80

        // sum
        int sum = people.stream().mapToInt(p -> p.getAge()).sum();
        System.out.println(sum);
        // 308

        // average
        double ave = people.stream().mapToInt(p -> p.getAge()).average().orElse(0.0);
        System.out.println(ave);
        // 44.0
    }
}

class Person {

    private String name;
    private Integer age;

    public Person(String name, Integer age) {
        this.name = name;
        this.age = age;
    }

    public Integer getAge() {
        return age;
    }

    public String getName() {
        return name;
    }

    public String toString() {
        return "name:" + name + " age:" + age;
    }
}