import java.util.Arrays;
import java.util.List;
import java.util.StringJoiner;
import java.util.stream.Collectors;

public class Example {

    public static void main(String[] args) {

        // String.join expects arguments of type CharSequence, or Iterable<CharSequence>
        // For example...
        // List<String> names = Arrays.asList("Tom", "Dick", "Harry");
        // String joined = String.join(",", names);

        // This program demonstrates how to join other kinds of objects.

        List<Person> people = Arrays.asList(
                new Person("Tom", 30),
                new Person("Dick", 27),
                new Person("Harry", 33));

        // Approach 1
        String joined = people.stream()
                .map(object -> object.getName())
                .collect(Collectors.joining(","));
        System.out.println("Approach 1. " + joined);

        // Approach 2
        StringJoiner joiner = new StringJoiner(",");
        people.stream().map(Person::getName).forEach(joiner::add);
        System.out.println("Approach 2. " + joiner.toString());
    }

}

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 void setName(String name) {
        this.name = name;
    }

    public int getAge() {
        return age;
    }

    public void setAge(int age) {
        this.age = age;
    }

}