How would I determine whether a number entered by a user contains the proper amount of numbers and - marks

Question

I'm new to Java programming and we are currently learning about Strings and Chars. My lab assignment is for the user to enter their SSN and for the program to determine whether it is a valid entry. The format entered needs to be 123-45-6789. So far this is what I have done: package Labs;

import java.util.Scanner;

public class Lab4 {

    public static void main(String[] args) {

        Scanner input = new Scanner(System.in);

        System.out.println("Enter a valid SSN");

        String ssn = input.nextLine();

        System.out.print(ssn);
        if (ssn.length() == 11) {
            if 


        }

    }
}

I've been looking on the forums here and have found some different answers, but when trying them in my code, something goes wrong. I'm not looking for anyone to write it out for me. What type of methods would I use to check that characters 0-2, 4-5, 7-10 contained a number and characters at 3 and 6 contain a -. Obviously charAt and contains would be helpful, but I'm not sure how to write out the conditions to determine this.

And this question asked How to tell if a SSN is in the right format which appears to be the exact same assignment, I assume we are using the same book doesn't actually give an answer, though its marked as a duplicate, which I can not find the original question. We haven't learned arrays yet either, so I am looking for a more simplistic answer, though I'm sure an example using arrays wouldn't hurt in addition to the simpler answer, so that I can develop my skills more.

Edit Update: Though I'm sure there's a better way to do this, it works.

public static void main(String[] args) {

    Scanner input = new Scanner(System.in);

    System.out.println("Enter a valid SSN");

    String ssn = input.nextLine();


    if (ssn.length() == 11 && 
            ssn.charAt(0)>='0' && ssn.charAt(0)<='9' && 
            ssn.charAt(1)>='0' && ssn.charAt(1)<='9' && 
            ssn.charAt(2)>='0'  && ssn.charAt(2)<='9' &&
            ssn.charAt(4)>='0'  && ssn.charAt(4)<='9' &&
            ssn.charAt(5)>='0'  && ssn.charAt(5)<='9' &&
            ssn.charAt(7)>='0'  && ssn.charAt(7)<='9' &&
            ssn.charAt(8)>='0'  && ssn.charAt(8)<='9' &&
            ssn.charAt(9)>='0'  && ssn.charAt(9)<='9' &&
            ssn.charAt(10)>='0'  && ssn.charAt(10)<='9' &&
            ssn.charAt(3)=='-' && ssn.charAt(6)=='-') 
            {
        System.out.println(ssn + " is a valid social security number");
    }
        else
            System.out.print(ssn + " is not a valid social security number");

    input.close();



}

}

Answer 1

First of all, I would avoid nested ifs, like that:

if (foo==bar) {
     if(that!=other) {
         if(...)
     }
}

This can quickly lead to chaos. Try to make your if statements parallel, not nested. Like that:

if (ssn.length() != 11) {
    System.out.print("SSN must be 11 letters long");
    return;
}

if (ssn.charAt(3)!='-' || ssn.charAt(7)!='-') {
    System.out.print("SSN must be 11 letters long");
    return;
}

Second, you need to check if a char is a digit. You can do that by a simple nummeric comparison:

if (ssl.charAt(0)<'0' || ssl.charAt(0)>'9') {
    System.out.print("Char at 0 was not a digit");
    return;
}

It would be also good practice to extract the repetitive part (like the is-digit check mentioned above) in a separate method. This way you avoid repeating yourself and you gain much better control over your program.

Hope this helps.