Converting all letters in the phone number to digits

Question

Im trying to replace each letter with a digit using the international standard letter/number mapping. I got my output to run correctly however, how do get the dashes in the phone number to appear automatically in the output? For example, if I enter 1800Flowers it prints out as 18003569377. How do I get it to print out as 1-800-3569377 without using regular expressions?

import java.util.Scanner;

public class PhoneKeypad {

public static void main(String[] args) {

    Scanner input = new Scanner(System.in);

    //while loop keeps the program running until the user enters quit 
    while (true) {
        System.out.println("\nEnter a phone number or quit to exit:");
        String phoneNumber = input.next();

        if (phoneNumber.equalsIgnoreCase("quit")) {              
            System.out.print("\nProgrammed by me");
            return;
        }

        //checks if the phone number entered is at least 8 digits
        if (phoneNumber.length() < 8) {
            System.out.println("Invalid Phone Number");

        } else {

            System.out.println(getNumber(phoneNumber));
        }
    }

}

//method converts all letters in the phone number to digits
public static String getNumber(String phoneNumber) {

    int keypadNum = 0;

    for (int i = 0; i < phoneNumber.length(); i++) {
        char letter = phoneNumber.charAt(i);

        if (Character.isAlphabetic(letter)) {
            letter = Character.toUpperCase(letter);

            switch (letter) {
                case 'A':
                case 'B':
                case 'C':
                    keypadNum = 2;
                    break;
                case 'D':
                case 'E':
                case 'F':
                    keypadNum = 3;
                    break;
                case 'G':
                case 'H':
                case 'I':
                    keypadNum = 4;
                    break;
                case 'J':
                case 'K':
                case 'L':
                    keypadNum = 5;
                    break;
                case 'M':
                case 'N':
                case 'O':
                    keypadNum = 6;
                    break;
                case 'P':
                case 'Q':
                case 'R':
                case 'S':
                    keypadNum = 7;
                    break;
                case 'T':
                case 'U':
                case 'V':
                    keypadNum = 8;
                    break;
                case 'W':
                case 'X':
                case 'Y':
                case 'Z':
                    keypadNum = 9;
                    break;
                default:
                    System.out.println("Invalid phone number");
            }

            phoneNumber = phoneNumber.substring(0, i) + keypadNum + phoneNumber.substring(i + 1);
        }
    }

    return phoneNumber;
}
}

Expected Output:

Answer 1

You could use a regular expression with String.replaceAll. Remove the leading one, group the first three digits, the second three digits and the final group of digits. Something like

public static String formatNumber(String phoneNumber) {
    if (phoneNumber.startsWith("1")) {
        phoneNumber = phoneNumber.substring(1);
    }
    return phoneNumber.replaceAll("(\\d{3})(\\d{3})(\\d+)", "1-$1-$2-$3");
}

or

public static String formatNumber(String phoneNumber) {
    return phoneNumber.replaceAll("1(\\d{3})(\\d{3})(\\d+)", "1-$1-$2-$3");
}

And then call it like

System.out.println(formatNumber(getNumber(phoneNumber)));

I ran it with 1800flowers and got (as expected)

1-800-356-9377

or without regular expressions like

public static String formatNumber(String phoneNumber) {
    if (phoneNumber.startsWith("1")) {
        phoneNumber = phoneNumber.substring(1);
    }
    return "1-".concat(phoneNumber.substring(0, 3)) //
            .concat("-").concat(phoneNumber.substring(3, 6)) //
            .concat("-").concat(phoneNumber.substring(6));
}

Before calling formatNumber, you can remove the dashes to normalize it with something like

public static String removeDashes(String phoneNumber) {
    StringBuilder sb = new StringBuilder();
    for (char ch : phoneNumber.toCharArray()) {
        if (ch != '-') {
            sb.append(ch);
        }
    }
    return sb.toString();
}

Then

System.out.println(formatNumber(removeDashes(getNumber(phoneNumber))));