Question

I have the following code generating 5-digit random numbers and adding them to an ArrayList. These numbers however must be unique ids.

for(int i = 0; i < myArr.length; i++) {
    int id = (int) (Math.round(Math.random() * 89999) + 10000);
    idArr.add(id);
}

I’m trying to work out how I could check to see if the number was already in the array before adding it but I can’t get my head around the best way to do this.

Answer 1

Use an ArrayList instead of an array. That way you would just need to use ArrayList#contains(obj) method to test whether the id is already in the ArrayList or not.

Or, you can just work with a HashSet, which will work faster with its HashSet#contains() method.