import java.util.Random;

public class Test {
    public static void main(final String[] args) {
        final String romaji = "abcdefghijklmnopqrstuvwxyz";
        final String number = "0123456789";
        final String generator = romaji + romaji.toUpperCase() +number;
        System.out.println(getStr(generator, 10));
        System.out.println(getStr(generator, 10));
        System.out.println(getStr(generator, 10));
    }

    private static String getStr(final String input, final int length) {
        final Random random = new Random();
        final int num = input.length();
        final StringBuilder sb = new StringBuilder();
        final char[] chars = input.toCharArray();
        for (int i = 0; i < 10; i++) {
            sb.append(chars[random.nextInt(num)]);
        }

        return sb.toString();
    }
}