How to Generate Unique ID in Java (Integer)?

Question

How to generate unique ID that is integer in java that not guess next number?

Answer 1

int uniqueId = 0;

int getUniqueId()
{
    return uniqueId++;
}

Add synchronized if you want it to be thread safe.

Answer 2

Just generate ID and check whether it is already present or not in your list of generated IDs.

Answer 3

 import java.util.UUID;

 public class IdGenerator {
    public static int generateUniqueId() {      
        UUID idOne = UUID.randomUUID();
        String str=""+idOne;        
        int uid=str.hashCode();
        String filterStr=""+uid;
        str=filterStr.replaceAll("-", "");
        return Integer.parseInt(str);
    }

    // XXX: replace with java.util.UUID

    public static void main(String[] args) {
        for (int i = 0; i < 5; i++) {
            System.out.println(generateUniqueId());
            //generateUniqueId();
        }
    }

}

Hope this helps you.

Answer 4

How unique does it need to be?

If it's only unique within a process, then you can use an AtomicInteger and call incrementAndGet() each time you need a new value.

Answer 5

Do you need it to be;

• unique between two JVMs running at the same time.
• unique even if the JVM is restarted.
• thread-safe.
• support null? if not, use int or long.

Answer 6

Unique at any time:

int uniqueId = (int) (System.currentTimeMillis() & 0xfffffff);