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Editorial Team
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Asked: 2026-05-25T23:19:38+00:00

Whenever I type in a phone number, this program below that I wrote to

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Whenever I type in a phone number, this program below that I wrote to format phone numbers from the user gives me back weird numbers that I did not even enter at all. Can someone please explain to me why I am getting such weird errors?

I want it so when someone enters just 12345678978 it will format to 1-234-567-8978
If they enter 2345678978 it will format to 234-567-8978
And if they enter 5678978 it will change to 567-8978.
I always get weird numbers that sometimes aren’t even what I entered like
12345678978 I get 144-34–567-
2345678978 I get 153-567-8978
5678978 I get 162-8978

I would really appreciate some help. Thanks.

    import java.util.Scanner;

    public class Test3 {
public static void main(String[] args) {
    Scanner y = new Scanner(System.in);
    String phoneNumber;
    int phoneNumberLength;
    System.out.print
        ("Please enter your phone number WITHOUT spaces or dashes: ");
    phoneNumber = y.nextLine();
    phoneNumberLength = phoneNumber.length();
    if (phoneNumberLength == 11) {
        phoneNumber = phoneNumber.charAt(0) + "-" + phoneNumber.charAt(1)
            + phoneNumber.charAt(2)
            + phoneNumber.charAt(3)
            + "-" + phoneNumber.charAt(4) + phoneNumber.charAt(5)
            + phoneNumber.charAt(6)
            + "-" + phoneNumber.charAt(7) + phoneNumber.charAt(8)
            + phoneNumber.charAt(9)
            + phoneNumber.charAt(10);
    }
    if (phoneNumberLength == 7) {
        phoneNumber = phoneNumber.charAt(0) + phoneNumber.charAt(1)
            + phoneNumber.charAt(2)
            + "-" + phoneNumber.charAt(3) + phoneNumber.charAt(4)
            + phoneNumber.charAt(5) + phoneNumber.charAt(6);
    }
    else {
        phoneNumber = phoneNumber.charAt(0) + phoneNumber.charAt(1)
            + phoneNumber.charAt(2)
            + "-" + phoneNumber.charAt(3) + phoneNumber.charAt(4)
            + phoneNumber.charAt(5)
            + "-" + phoneNumber.charAt(6) + phoneNumber.charAt(7)
            + phoneNumber.charAt(8)
            + phoneNumber.charAt(9);
    }
    System.out.println("So your phone number is " + phoneNumber + "?");
}

By the way. I know it is not formatted correctly but I am very confused with how stackoverflow allows you to add code.

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1 Answer

  1. Editorial Team

    Any string that starts like this:

    number = number.charAt(0) + number.charAt(1) + ...

    will cause the problem, because you are adding two char types together. This is treated as integer arithmetic, not string concatenation. It would be a lot better to add substrings together, so that the operator is string concatenation, instead of integer addition.

    number = number.substring(0, 3) + '-' + number.substring(3, 6) + ...
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