Chapter 21 Exercise 12, Introduction to Java Programming, Tenth Edition Y. Daniel LiangY.

21.12  (Name for both genders)
Write a program that prompts the user to enter one of the filenames described
in Programming Exercise 12.31 and displays the names that are used for both
genders in the file. Use sets to store names and find common names in two sets.

import java.io.File;
import java.io.FileNotFoundException;
import java.util.HashSet;
import java.util.Iterator;
import java.util.Scanner;

public class Exercise_12 {

    public static void main(String[] args) throws FileNotFoundException {

        System.out.print("Choose an year to see its baby name rankings (2001-2010): ");
        Scanner in = new Scanner(System.in);
        String path = "babynamesranking" + in.nextInt() + ".txt";
        in.close();


        in = new Scanner(new File(path));

        HashSet<String> boyNames = new HashSet<>();
        HashSet<String> girlNames = new HashSet<>();

        while (in.hasNext()) {
            in.nextInt(); // rank (trash)
            boyNames.add(in.next()); // boy name
            in.nextInt(); // popularity (trash)
            girlNames.add(in.next()); // girl name
            in.nextInt(); // popularity (trash)
        }

        boyNames.retainAll(girlNames);
        System.out.println(boyNames.size() + " names used for both genders.");
        System.out.print("They are ");
        Iterator iterator = boyNames.iterator();
        int count = 1;
        while (iterator.hasNext()) {
            System.out.print(iterator.next() + ", ");
            if (count % 10 == 0)
                System.out.println();
            count++;
        }
    }

}