Rite a program that inserts parentheses, a space, and a dash into a string of 10 user-entered numbers to format it as a phone number. For example, 5153458912 becomes (515) 345-8912. If the user does not enter exactly 10 digits, display an error message. Continue to accept user input until the user enters 999. Save the file as PhoneNumberFormat. java.

import java.util.Scanner;

public class PhoneNumber

{

public static void main(String[] args) {

    Scanner input = new Scanner(System.in);

       while(true) {

           System.out.print("Enter the phone number :");

           String phoneNumber = input.nextLine();

           if(phoneNumber.contains("999"))

               break;

           if(phoneNumber.length() == 10){

               phoneNumber = phoneNumber.replaceFirst("(\\d{3})(\\d{3})(\\d+)", "($1) $2-$3");

               System.out.printf("The formatted phone number is: %s \n", phoneNumber);

           }

           else

               System.out.println("The phone number must be exactly 10 digits!");

       }

}

}

Explanation:

- Unless we specify a breaking condition inside the while loop, it will iterate

- Ask the user for the phone number to be formatted

- Check if the phone number is 999, if yes, stop the loop

- If the phone number contains exactly 10 digits, format the phone number as requested using regex

- Print the formatted phone number

- If it has not 10 digits, print an error message