How to generate sequential alphanumeric string in Java starting with specific string

Question

I want to be able to generate sequential alphanumeric strings of a given length 8. Also, I want the string to start with a specific string let's say "ABC00". Just imagine a license plate starts with a specific string and other generated alphanumeric strings. I have tried a number of things I have seen here and not getting the desired results.

This is what I currently have

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

public class RandomString {


    static final String AB = "SCV00" + "0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz";
    static SecureRandom rnd = new SecureRandom();

    String randomString(int len){
        StringBuilder sb = new StringBuilder(len);
        for(int i = 0; i < len; i++)
            sb.append(AB.charAt(rnd.nextInt(AB.length())));
        return sb.toString();
    }

}

I want my output to look like this. When users provide the number of IDs they want I should be able to generate it. Say, user wants 3 IDs. I should have. So, I just read the requirement properly and there is a slight difference.

Lowercase will be eliminated. This is how the format should look like. The starting string is "CLV0".

CLVO 0001
CLV0 0002
CLV0 0003
:
CLV0 0009
CLV0 000A
CLVO 000B
:
CLV0 000Z
CLV0 0010

This is the actual sequence. It's not random. Kindly help with this

Answer 1

I'll assume you need 0000 to 000Z, then 0010, 0011, 0012 and so on. You would need to keep track of the current id you need to generate. Something like this:

public class SequentialString {

    private static final String START = "CLV0";
    private static final String ALPHANUMERIC = "0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ";

    public static void main(String[] args) {
        int totalLength = 8;
        int numberOfIds = 111;
        int countRemainingSymbols = totalLength - START.length();
        for (int i = 0; i < numberOfIds; i++) {
            StringBuilder end = new StringBuilder();
            int current = i;//depending on exact case, you would need to keep track of current
            int remainder = current % ALPHANUMERIC.length();//the index of next character
            do {
                end.append(ALPHANUMERIC.charAt(remainder));
                current /= ALPHANUMERIC.length();//update to check if we need to add more characters
                remainder = current % ALPHANUMERIC.length();//update index, only used if more chars are needed
            } while (current > 0);
            int padCount = countRemainingSymbols - end.length();
            StringBuilder result = new StringBuilder(START).append("-");//- is for easier debugging, remove it for your case
            for (int j = 0; j < padCount; j++) {
                result.append("0");
            }
            result.append(end.reverse());
            System.out.println(result);
        }
    }
}

Basically, using current and length of ALPHANUMERIC to calculate next char index, then calculate if more characters are needed, keep looping until no more chars are needed. Note that i am reversing generated sequence(variable end in code) before appending it.

Also note that this solution is not limited to ZZZZ, it can keep generating the sequence even after that.

Answer 2

You could leverage UUID here:

String uuid = UUID.randomUUID().toString().replace("-", "");
String randomString = "SCV00" + uuid.substring(0, 5);
System.out.println(randomString);  // SCV00f044d