User friendly random code generator

RandomCodeGenerator.java

import java.security.SecureRandom;
import java.util.Random;

public class RandomCodeGenerator {

    static final SecureRandom RANDOM = new SecureRandom();
    static final char[] LETTERS = "ABCEFGHJKMNPQRSTWXYZ".toCharArray();
    static final char[] NUMBERS = "0123456789".toCharArray();
    static final int DEFAULT_NUM_CODES = 20;

    public static void main(String[] args) {

        int numCodes = DEFAULT_NUM_CODES;

        if (args.length >= 1) {
            numCodes = Integer.parseInt(args[0]);
        }

        System.out.println("======================================================");
        System.out.println("");
        for (int i = 0; i < numCodes; i++) {
            System.out.println("    " + randomCode(RANDOM));
        }
        System.out.println("");
        System.out.println("======================================================");


    }


    private static String randomCode(Random rng) {
        StringBuilder sb = new StringBuilder();
        randomTriplet(rng, sb);
        sb.append('-');
        randomTriplet(rng, sb);
        sb.append('-');
        randomTriplet(rng, sb);
        sb.append('-');
        randomTriplet(rng, sb);

        return sb.toString();
    }

    private static StringBuilder randomTriplet(Random rng, StringBuilder sb) {
        return sb.append(randomChar(rng, NUMBERS))
                //.append(randomChar(rng, LETTERS))
                .append(randomChar(rng, NUMBERS))
                .append(randomChar(rng, NUMBERS));
    }
    
    private static char randomChar(Random rng, char[] alphabet) {
        return alphabet[rng.nextInt(alphabet.length)];
    }

}