How do I put together numbers in java?

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 + random开发者_JS百科Number2 + randomNumber3;
        String userName = initials + randomNumbers;
        System.out.println("Your username is " + userName +  ".");
    }
}

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;

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);

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.

Suppose you have three numbers:

int randomNumber1 = 3;
int randomNumber2 = 4;
int randomNumber3 = 5;
int randomNumbers = randomNumber1 + randomNumber2 + randomNumber3;

Do you expect randomNumbers to be 345? Or do you expect it to be 12?

Now try this:

String randomNumbers = "" + randomNumber1 + randomNumber2 + randomNumber3;

What do you get this time?

Try,

String userName=String.format("%s%d%d%d",initials,randomNumber1,randomNumber2,randomNumber3);

randomNumbers = randomNumber1 + randomNumber2 + randomNumber3;

You're adding the numbers, not concatenating them.

Suggested solution: use only 1 random number with

generator.nextInt(1000);

Or, you can go like:

String userName = initials + randomNumer1 + randomNumber2 + randomNumber3;

But I'm nearly sure you'll get 2 or even 3 times the same number, so you should use the first approach instead.

You are adding the numbers here.

randomNumbers = randomNumber1 + randomNumber2 + randomNumber3;

If you want to achieve what you are looking for using this same method you could do.

randomNumbers = randomNumber1 + (randomNumber2 * 10) + (randomNumber3 * 100);

What's wrong is that the + operator does an addition, and not a concatenation when used on int variables.

Use

String randomNumbers = Integer.toString(randomNumber1) + Integer.toString(randomNumber2) + Integer.toString(randomNumber3);

to convert the numbers into strings and concatenate them.

You are adding three digits, that would at most give you 27. You want to concatenate the string representation of those digits.

That said, why don't you simply generate a random number between 0 and 999?