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I am writing an android app giving each client a long user ID through this formula:
long userID = (long) (Math.random() * 2 * Long.MAX_VALUE - Long.MAX_VALUE);
Am I utilizing MAX_VALUE correctly i.e. taking advantage of every possible long value?
What are my chances of having two duplicate user IDs with 10k, 100k or 1m users? How could I calculate this?
You can make use of either one of those mentioned below:
Instead of using the random to get a long user id, use current date and time expressed in milliseconds.
Use a Random UUID