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

It should follow an order sort of. Let's say SCV00Axyz, SCV00Apyt, SCV00Buye, etc — Curious, Mar 10 '22 at 11:11
"It should follow an order sort of", what are the exact rules you expect? Why comes `Axyz` before `Apyt`, and `Buye` at last? — sp00m, Mar 10 '22 at 11:16
Okay. So, I want the alphabet that Comes immediately after is important. SCV00A"aplhanumericString", SCV00BalphanumericString, SCV00CalphanumericString, etc — Curious, Mar 10 '22 at 11:29
@Curious The sequence from `0001` to `000Z` is obvious, but what comes after `0010`? Is it `0020`, `0030` and so on? Or is it `0011`, `0012` and so on? Or something else? — Chaosfire, Mar 10 '22 at 16:33

Chaosfire · Accepted Answer · 2022-03-10T17:50:18.990

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.

Thanks a lot. I am going to update my question now. Kindly check — Curious, Mar 10 '22 at 15:12
@Curious Check new solution, answer got completely overhauled. — Chaosfire, Mar 10 '22 at 17:52
I want to save this in the db or a tempFile. Such that, when next a user makes the request, it doesn't start all over again. It starts from the last time it stops. Kindly help. Thanks — Curious, Mar 15 '22 at 22:28
@Curious Make another question, which includes the setup of your program, so people can suggest correct solution. Currently there is not enough information, the best i can help with is that you need to save the value of `current` and start next generation with next value of `current`. — Chaosfire, Mar 16 '22 at 07:58
here is the link to the new question. Kindly go through it. Thanks https://stackoverflow.com/questions/71504860/how-to-save-alphanumeric-sequence-in-mongodb-and-start-generating-from-the-last — Curious, Mar 16 '22 at 22:19

score -1 · Answer 2 · answered Mar 10 '22 at 11:04

-1

You could leverage UUID here:

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

answered Mar 10 '22 at 11:04

Tim Biegeleisen

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

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