About generating unique random numbers

Question

  public String generateCustomerID(String id, int digit)//Customer Class

   randomGenerator = new Random();

   String index = "";

   for(int i = 1; i <= digit; i++)
   {  

       index +=  randomGenerator.nextInt(10);

   }
      return id + index;

   public void storeCustomer(Customer customer)//Shop Class
   {
    customerList.add(customer);
    HashSet<String> set = new HashSet<>();
    String number =   customer.generateCustomerID("AB", 1);

    set.add(number);
    customer.setCustomerID(number);

   }

How can i make sure that only customers with unique id are stored. For example, if customer A got id "AB-1", then customer B should have a different id like "AB-8". I tried to use Hashset but but i am not sure this is the right method to solve this problem. I do not think i need to use UIDD.

do you have a problem with making unique ids or a problem with the collection you're using? — 4dc0, Apr 27 '17 at 02:13
Are these customers ultimately getting stored in a database? At what scope do they need to be unique? — Michael Markidis, Apr 27 '17 at 02:15
Possible duplicate of [How do I create a unique ID in Java?](http://stackoverflow.com/questions/1389736/how-do-i-create-a-unique-id-in-java) — Rahul Sharma, Apr 27 '17 at 02:19
You are defining your `set` within `storeCustomer` so it will be recreated everytime you call this method - move it as a field. Also you do not seem to be checking this set to see if the number exists — Scary Wombat, Apr 27 '17 at 02:23
Not stored in a database. Each customer should have an unique id. — James Tomy, Apr 27 '17 at 02:23

score 0 · Accepted Answer · answered Apr 27 '17 at 02:46

0

consider this solution

    static Set<String> taken = new HashSet <>();
    public static void main(String [] args)
    {
        Scanner scan = new Scanner (System.in);
        while (true) {
            System.out.println("enter id ");
            String id = scan.nextLine();
            if (taken.contains(id)) {
                System.out.println("already taken");
                continue;
            }
            taken.add (id);
            System.out.println("another [y/n]? ");
            if (scan.nextLine().equals("n"))
                break;
        }
    }

the key point being that set is a field and it is checked using contains

answered Apr 27 '17 at 02:46

Scary Wombat

44,617
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I see. Does this code just check whether the id is already taken? – James Tomy Apr 27 '17 at 03:00
Yes, `if (taken.contains(id)) {` – Scary Wombat Apr 27 '17 at 03:34
I tried your code but i do not know how to store the id into the customer. – James Tomy Apr 27 '17 at 03:41
well as per your original code `customer.setCustomerID(number);` just replace `number` with my more meaningful named variable `id` – Scary Wombat Apr 27 '17 at 04:02

wylasr · Answer 2 · 2017-04-27T02:29:09.360

-3

place
while(set.contains(number)){ number = customer.generateCustomerID("AB", 1); } before set.add(number);customer.setCustomerID(number);

edited Apr 27 '17 at 02:29

answered Apr 27 '17 at 02:24

wylasr

117
9

maybe `!contains` ? – Scary Wombat Apr 27 '17 at 02:25
sorry it should be `contains(number)`.but what's the problem with my answer? – wylasr Apr 27 '17 at 02:31
see my comment below the OP's question – Scary Wombat Apr 27 '17 at 02:33
@James Tomy place `HashSet set = new HashSet<>();`in your class as an instance. – wylasr Apr 27 '17 at 02:40

About generating unique random numbers

2 Answers2