Adding a duplicate to a Set

Predict the outputEasyJava only

Main.java

import java.util.*;

public class Main {
    public static void main(String[] args) {
        Set<String> set = new HashSet<>();
        System.out.println(set.add("a"));
        System.out.println(set.add("a"));
        System.out.println(set.size());
        System.out.println(set.contains("a"));
    }
}

What does it print?

Graded by exact match. Spaces at the ends of lines and blank lines at the end do not count.

to answer and keep your progress. Reading is free for everyone.