[hardwired]

I dont quite understand, the userPhoneTwo is already parsed to an integer in that first line
Yes, you're right. Sorry, I didn't look closely enough before answering.

Code:

public class Test {
    public static void main(String[] args) {
        // b. The phone number of the customer is not blank and
        //    doesn’t exceed 10 characters and is an integer
        //    with positive number only
        String userPhone = "1234567890";
        // Tests for blank phone number:
        // userPhone.equals("") _or_ userPhone.length() == 0
        // Test for integer value:
        // userPhone.indexOf(".") == -1
        boolean hasDecimal = userPhone.indexOf(".") != -1;
        if(hasDecimal)
            JOptionPane.showMessageDialog(null, "Not an integer value");
        // Or you could catch a NumberFormatException in parsing the string.
        System.out.println("Integer.MAX_VALUE = " + Integer.MAX_VALUE);
        // Eleven digit numbers are too big for an int size
        // so use long data type. Or you could catch an exception
        // in parsing the string as an int.
        long phoneNumber = Long.parseLong(userPhone);
        System.out.printf("userPhone = %s  phoneNumber = %d%n",
                           userPhone, phoneNumber);
        int length = userPhone.length();
        if (length == 0 || length > 10 || phoneNumber < 0) {
            JOptionPane.showMessageDialog(null, "Phone number cannot be " +
                     "longer than 10 digits and must be a positive integer");
            System.exit(0);
        }
    }
}