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I would like to generate a ten digit account number greater than 1,000,000,000 and less than 9,999,999,999. I have 3 separate attempts that all are almost operational, but after 9 digits I either receive an error or a number that is generated is not an expected outcome.

        for(int i = 0; i < 10; i++) {
            int r = rand.nextInt(10);
            int l = (int)Math.pow(10,i);
            int currentRand = r * l;
            System.out.println("i: "+ i+ ", random int: "+ r+", ten to the pow i: "+ l+ ", currentRand: "+ currentRand);
        }

        int n = rand.nextInt(89999) + 10000;
        int n1 = rand.nextInt(89999) + 10000;
        int n2 = Math.multiplyExact(n*100000);
        System.out.println(n);
        System.out.println(n1);
        System.out.println(n2);

    int accountNum;
        String ofNumber = "";
        for(int i = 0; i < 10;i++) {
            ofNumber += String.valueOf(rand.nextInt(10));
            System.out.println(ofNumber);
        }
        accountNum = Integer.parseInt(ofNumber);
Mark-Chi
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  • A minor point. Your most significant digit should be in the range [1..9] not [0..9] to avoid a leading zero and hence a nine-digit number. – rossum Feb 16 '21 at 08:48

2 Answers2

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The largest value representable as an int is 2147483647, so about 78% of the 10-digit number range is larger than what can be stored in an int. Use either long or BigInteger.

Jim Garrison
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As Jim Garrison says, your account numbers won't fit into an int but they will fit into a long.

The Random class allows you to generate a stream of random long numbers between a minimum (inclusive) and a maximum (exclusive). Here is an example of this that prints out 10 account numbers:

I have assumed that the smallest account number you want is 1000000000 and the largest 9999999999

import java.util.Random;

public class AccountNumberDemo {
    public static void main(String[] args) {
        Random rand = new Random();
        rand.longs(10, 1_000_000_001L, 10_000_000_000L)
            .forEach(System.out::println);
    }
}

If you just want one account number in a variable, then this shows how to do it:

import java.util.Random;

public class AccountNumberDemo {
    public static void main(String[] args) {
        Random rand = new Random();
        long accountNumber = rand
                .longs(1, 1_000_000_001L, 10_000_000_000L)
                .findFirst()
                .getAsLong();
        System.out.println(accountNumber);
    }
}
Chris Foley
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