How can I prevent the overlapping random numbers

Question

How would i prevent duplicating numbers from random numbers. I need to generate 5 numbers between 1 and 9 that are each different. I would often get same numbers like 23334, how can i prevent that? Any help would be great!

    int num2 = (int) Math.round((Math.random()*9) +1);
    int num1 = (int) Math.round((Math.random()*9) +1);
    int num5 = (int) Math.round((Math.random()*9) +1);
    int num3 = (int) Math.round((Math.random()*9) +1);
    int num4 = (int) Math.round((Math.random()*9) +1);

Answer 1

One option is to use shuffle algorithm (e.g. Fisher-Yates shuffle ) to generate random sequence from 1 to 9, then take first 5 numbers of the sequence

Further explanation on StackOverflow: https://stackoverflow.com/a/196065/950427

Answer 2

Set<Integer> set=new HashSet<>();
while (set.size()<5) {
    set.add( Math.round((Math.random()*9) +1));
}

After the set is filled you have 5 unique random numbers.

UPDATE: just to illustrate Jared Burrows' comment