gistfile1.txt

import java.util.Scanner;

    public class SampleMain {

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

            // validate input
            String validInput = validateInput(scanner);
        
            // valid input
            System.out.println("Valid input: " + validInput);
	    }
	
	    private static String validateInput(final Scanner scanner) {
	        String input = scanner.nextLine();
		
            // if the input contains a letter request new input
		    while (input.matches(".*[a-zA-Z]+.*")) {
			    System.out.println("Input string cannot contain letters, please try again...");	
        	    input = scanner.nextLine();  	
            }
		
		    return input;
        }
    }