How to be sure that random numbers are unique and not duplicated?

Question

I have a simple code which generates random numbers

SecureRandom random = new SecureRandom();
...
public int getRandomNumber(int maxValue) {
    return rando         


        

Answer 1

A random sequence does not mean that all values are unique. The sequence 1,1,1,1 is exactly as likely as the sequence 712,4,22,424.

In other words, if you want to be guaranteed a sequence of unique numbers, generate 10 of them at once, check for the uniqueness condition of your choice and store them, then pick a number from that list instead of generating a random number in your 10 places.