Generate Random String in java

Question

I'm trying to generate a string between capital A-Z in java using Secure Random. Currently I'm able to generate an alphanumeric string with special characters but I want a string with only upper case alphabets.

  public String createRandomCode(int codeLength, String id){   
     char[] chars = id.toCharArray();
        StringBuilder sb = new StringBuilder();
        Random random = new SecureRandom();
        for (int i = 0; i < codeLength; i++) {
            char c = chars[random.nextInt(chars.length)];
            sb.append(c);
        }
        String output = sb.toString();
        System.out.println(output);
        return output ;
    } 

The input parameters are length of the output string & id whhich is alphanumeric string.Can't understand what modifications to make to the above code to generate only upper case alphabet string. Please help..

Answer 1

Here is generator that I wrote and use:

public class RandomGenerator {
    private static final String characters = "ABCDEFGHIJKLMNOPQRSTUVWXYZ";

    public static String generateRandom(int length) {
        Random random = new SecureRandom();
        if (length <= 0) {
            throw new IllegalArgumentException("String length must be a positive integer");
        }

        StringBuilder sb = new StringBuilder(length);
        for (int i = 0; i < length; i++) {
            sb.append(characters.charAt(random.nextInt(characters.length())));
        }

        return sb.toString();
    }
}

in numChars string you can put any characters you want to be included. int length parameter is the length of generated random string.