how to make Unique ID for regestered members?

**RedElvaan** · May 21st, 2014, 04:55 AM

Hi,

I am developing a JAVA code to generate UID for registered members which contains two digits related to year of register and 6 random integers.

I have this code but it only generates three UID's I need to generate one UID when ever this code is run, and how to validate that this UID is really unique and not repeated?

import java.util.Date;
import java.util.HashMap;
public class StudentsID 
{
    private Date regDate;
    private static int idCount;
    private static HashMap<String,Integer> student_ids;
    public StudentsID()
    {
        regDate=new Date();
        student_ids=new HashMap<String,Integer>();
 
        idCount++;
 
 
    }
    public int makeID()
    {
        int step4=0;
 
        String step2;
        String step3;
        if(regDate.getYear()>99)
        {
            String step1=String.valueOf(regDate.getYear());
            step2=step1.substring(1);
        }
        else
            step2=String.valueOf(regDate.getYear());
 
        if(idCount<1000000)
        {
        step3=step2+0+0+0+0+0+0;
        step4= Integer.parseInt(step3)+idCount;
        }
        return step4;
    }
 
    public static void main(String...args)
    {
        StudentsID test1=new StudentsID();
        System.out.println(test1.makeID());
 
        StudentsID test2=new StudentsID();
        System.out.println(test2.makeID());
 
        StudentsID test3=new StudentsID();
        System.out.println(test3.makeID());
 
    }
 
}

**GregBrannon** · May 21st, 2014, 06:27 AM

Welcome to the Forum! Thanks for taking the time to learn to post code correctly, and if you haven't already, please read this topic to see other useful info for newcomers.

Why do the 6 integers have to be random? It would be easiest if they started at 000001 and then counted up with each new member. Creating the six digits randomly and checking for uniqueness each time a member is added is more trouble than I think it's worth.

**RedElvaan** · May 21st, 2014, 07:13 AM

Hi Greg,

I think what you saying is right starting from 000001 as serial is better to reduce the validation process and to save time, but the thing is I need to include/attach to these digits two more digits from the left which is related to the year of registration

ex.

date of register : 21.05.2014 so java will take 14 from the year 2014 and add it to the serial number 000001 to be 14000001. This way the system will have up to 999999 available for members registered in 2014 and so on for next year if you get my point?!

**Cornix** · May 21st, 2014, 07:16 AM

So, what do you have problems with? What is your question?

**RedElvaan** · May 21st, 2014, 07:20 AM

ops sry :p

Ok could you give code examples to generate serial numbers?

**GregBrannon** · May 21st, 2014, 07:26 AM

I won't give you code, but I suggest you check out the following topics:

class variables or fields
StringBuilder class

and consider how those could be used to accomplish what you're trying to do.

**RedElvaan** · May 21st, 2014, 07:38 AM

Thanks for your kind help

**Cornix** · May 21st, 2014, 08:20 AM

You could also do it without strings. You only need very basic math for this.

If you want to shift a number to the left by a certain number of digits you just multiply with a power of 10.
For example: 14 * 10^6 == 14 000 000

And if you want the last 2 digits of a number you can do modulo calculation with a power of 10.
For example: 2014 % 10^2 == 14

So if you are given the year and a number of 6 random digits you can simply do:
(year % 10^2) * 10^6 + rndNum

For year == 2014 and rndNum == 123456 the result would be:
(2014 % 10^2) * 10^6 + 123456
== (2014 % 100) * 1000000 + 123456
== 14 * 1000000 + 123456
== 14000000 + 123456
== 14123456

which is what you want.

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