java error

[jcaccia]

With a Scanner you can check the token before reading it:

Scanner sc = new Scanner(System.in);
int n;
do {
	System.out.append("Enter a number: ");
	if (sc.hasNextInt()) {
		n = sc.nextInt();
		break;
	} else {System.out.format("%nERROR: %s is not an integer number!%n%n", sc.nextLine());}
} while (true);

This will loop until the user types an integer number, rejecting strings or other numbers that cannot be read as integer.