Question

For some reason when I run the following code the program prints out “JDN4” or “JDN16” when at all times I want it to be printing “JDN” followed by three numbers ranging from 0-9; for example, “JDN123” or “JDN045” or “JDN206”. What is wrong with the code?

import java.util.*;

public class Document2 {
    public static void main(String[] args) {
        String initials = "JDN";
        int randomNumbers;
        Random generator = new Random();
        int randomNumber1 = generator.nextInt(9);
        int randomNumber2 = generator.nextInt(9);
        int randomNumber3 = generator.nextInt(9);
        randomNumbers = randomNumber1 + randomNumber2 + randomNumber3;
        String userName = initials + randomNumbers;
        System.out.println("Your username is " + userName +  ".");
    }
}

Answer 1

Your problem is randomNumbers is declared as an int, so when you use the + on the other ints, it will sum the integers rather than concatenate them.

So, if we were to use your approach, we’d need a string:

String userName = initials + randomNumber1 + randomNumber2 + randomNumber3;

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But it would be a lot easier just to generate a number from 0-999 and pad it with zeroes:

int randomNumber = generator.nextInt(1000);
String usernName = initials + String.format("%03d", randomNumber);

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Something else worth noting is that Random.nextInt(n) generates a random number between 0 (inclusive) and n (exclusive), so you probably should be doing .nextInt(10) if you want a number between 0 and 9.