How to serialise an array of 2 lists in a binary file?

I am creating a Java program that reads two text files, selects 10 words at random from each file and stores them in an array of two string lists. I have created the following code so far, however this only reads the words, it doesn't store them. I also need to serialize the array of 2 lists in a binary file. How can this be done? Some help with this would be greatly appreciated!

import java.io.File;
import java.io.FileNotFoundException;
import java.util.ArrayList;
import java.util.Random;
import java.util.Scanner;

public class RandomWordGenerator {

public static void main(String[] args) throws FileNotFoundException {
System.out.println(randomFromFile("file1.txt", 10));
System.out.println(randomFromFile("file2.txt", 10));

}

private static ArrayList<String> randomFromFile(String fileName, int count) throws FileNotFoundException {
    Scanner scanner = new Scanner(new File(fileName));
    ArrayList<String> words = new ArrayList<>();
    while (scanner.hasNext()) {
        words.add(scanner.next());
    }
    return randomFromWords(words, count);
}

static private ArrayList<String> randomFromWords(ArrayList<String> words, int count) {
    ArrayList<String> randomWords = new ArrayList<>();
    for (int i = 0; i < count; ) {
        int random = new Random().nextInt(words.size());
        if (randomWords.add(words.get(random))) {
            i++;
        }
    }
    return randomWords;
   }
}