Lambda practice(do not know what is the problem)

First Lambda practice

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

public class PersonFindErr {
    public static void main(String[] args) {
        List<Person> persons = new ArrayList<>();
        persons.add(new Person("name10", 10));
        persons.add(new Person("name20", 20));
        persons.add(new Person("name30", 30));
        persons.add(new Person("name40", 40));
        persons.add(new Person("name50", 50));
        System.out.println("-- 1 filter ---------------------------");
        persons.stream().filter(p->p.getAge() >= 30).forEach(p -> System.out.println("★1  30以上:" + p.getName()));        
        System.out.println("-- 2 findFirst ---------------------------");
        Optional<Person>  xxx = persons.stream().filter(p->p.getAge() == 20).findFirst();
        System.out.println("★2 firstPerson:" + xxx);
        System.out.println("-- 3 map & sum  ---------------------------");
        int total = persons.stream().map(p->p.getAge()).sum();
        System.out.println("total:" + total);
        System.out.println("-- 4 map & forEach  ---------------------------");
         persons.stream().filter(p->p.getAge() < 20).map(p->p.getAge()).forEach(p->System.out.println("★4 map forEach:" + p));
        System.out.println("-- 5 map & into  ---------------------------");
        List<Person> list = persons.stream().filter(p->p.getAge() <= 20).into(new ArrayList<>());
        list.forEach(p-> System.out.println("★5 map Into:" + p.getName()));
    }
}