lambda & regex function

import java.util.ArrayList;
import java.util.Random;

public class Regulars {
    public static void main(String[] args) {
        ArrayList<String> nya = new ArrayList<>();
        // fill list with random strings containing both letters and numbers
        Random random = new Random();
        for (int i = 0; i < 10; i++) {
            StringBuilder sb = new StringBuilder();
            for (int j = 0; j < 10; j++) {
                if (random.nextBoolean()) {
                    sb.append((char) (random.nextInt(26) + 'a'));
                } else {
                    sb.append((char) (random.nextInt(10) + '0'));
                }
            }
            nya.add(sb.toString());
        }
        // duplicate values and add in the same list
        for (int i = 0; i < 10; i++) {
            nya.add(nya.get(random.nextInt(nya.size())));
        }

        //nya.forEach(System.out::println);

        // using lambda expressions print sorted all non-empty unique strings that contain only letter
        nya.stream()
                //regex to delete nums
                .map(x -> x.replaceAll("[0-9]", ""))
                .filter(x -> !x.isEmpty())
                .distinct()
                .filter(x -> x.matches("[a-z]+"))
                .sorted()
                .forEach(System.out::println);


    }

}