Scanner Input Validation

Question

Hi, I hope Im posting to the right place.
I want to check to see if the user input is an integer and keep asking for one if the input is not an integer. Should be very simple but I cant do it because I just dont know how. Im not willing to use a "try and catch" since I dont know how to use that either.
This is what I got...
     int num;
     System.out.print("Please enter a number? ");
     Scanner sc = new Scanner(System.in);
     while (!sc.hasNextInt())
          System.out.println("That is NOT an Integer!");
          System.out.print("Please enter a number? ");
     num = sc.nextInt();
     System.out.println(num + " is an Integer!");Thank you...

Answer 1

This is what I did in a recent project(I use BufferedReader, not Scanner). There are actually quite a few ways to do it. You can check the each char to see if they are between 0-9, but a try/catch right in main but I found this to be most effective to keep the program running. It's not the fastest running time from what I've tried(checking each char to be 0-9 was probably fastest) but if you want full proof do something like this.
public class Test{
     public static boolean isInteger(String string){
          try{
               Integer.parseInt(string);
               return true;
          catch(NumberFormatException nfe){
               return false;
           public static void main(String[] args){
                String input;
                int n;
                BufferedReader in = new BufferedReader(new InputStreamReader(System.in));
          //gets the number of students to input
          System.out.println("How many students are there?");
          try{
               input = in.readLine();
          catch (IOException ioe){
               System.out.println("IO error trying to read input");
                   System.exit(1);
               while(!isInteger(input) || input.equals("")){
                  System.out.println("Not a number, please input a number");
               try{
                    input = in.readLine();
               catch (IOException ioe){
                    System.out.println("IO error trying to read input");
                        System.exit(1);
             n = Integer.parseInt(input);