Тут всё Ясно

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

public class Person {
    private String name;
    private int age;

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

    public String getName() {
        return name;
    }

    public int getAge() {
        return age;
    }

    public static List<String> getNamesOfAdults(List<Person> people) {
        List<String> adultNames = new ArrayList<>();
        for (Person person : people) {
            if (person.getAge() >= 18) {
                adultNames.add(person.getName());
            }
        }
        return adultNames;
    }

    public static void main(String[] args) {
        List<Person> people = new ArrayList<>();
        people.add(new Person("Alice", 25));
        people.add(new Person("Bob", 17));
        people.add(new Person("Charlie", 30));

        List<String> adultNames = getNamesOfAdults(people);
        System.out.println("Names of adults: " + adultNames);
    }
}