(Check SSN) Write a program that prompts the user to enter a Social Security number in the format DDD-DD-DDDD, where D is a digit. Your program should check whether the input is valid. Here are sample runs:

/*
(Check SSN) Write a program that prompts the user to enter a Social Security
number in the format DDD-DD-DDDD, where D is a digit. Your program should
check whether the input is valid.
*/
import java.util.Scanner;

public class Exercise_04_21 {
	public static void main(String[] args) {
		Scanner input = new Scanner(System.in);

		// Prompt the user to enter a Social Security number
		System.out.print("Enter a SSN: ");
		String ssn = input.nextLine();

		// Check whether the input is valid
		boolean isValid = 
			(ssn.length() == 11) && 
			(Character.isDigit(ssn.charAt(0))) &&
			(Character.isDigit(ssn.charAt(1))) &&
			(Character.isDigit(ssn.charAt(2))) &&
			(ssn.charAt(3) == '-') &&
			(Character.isDigit(ssn.charAt(4))) &&
			(Character.isDigit(ssn.charAt(5))) &&
			(Character.isDigit(ssn.charAt(7))) &&
			(ssn.charAt(6) == '-') &&
			(Character.isDigit(ssn.charAt(8))) &&
			(Character.isDigit(ssn.charAt(9))) &&
			(Character.isDigit(ssn.charAt(10)));

		// Display result
		System.out.println(ssn + " is " + ((isValid) ? "a valid " : "an invalid ")
			+ "social security number");
	}
}