How to use Scanner to accept only valid int as input

Question

I'm trying to make a small program more robust and I need some help with that.

Scanner kb = new Scanner(System.in); int num1; int num2 = 0;  System.out.print("Enter number 1: "); num1 = kb.nextInt();  while(num2 < num1) {     System.out.print("Enter number 2: ");     num2 = kb.nextInt(); } 

1. Number 2 has to be greater than number 1

2. Also I want the program to automatically check and ignore if the user enters a character instead of a number. Because right now when a user enters for example r instead of a number the program just exits.

Answer 1

Use Scanner.hasNextInt():

Returns true if the next token in this scanner's input can be interpreted as an int value in the default radix using the nextInt() method. The scanner does not advance past any input.

Here's a snippet to illustrate:

Scanner sc = new Scanner(System.in); System.out.print("Enter number 1: "); while (!sc.hasNextInt()) sc.next(); int num1 = sc.nextInt(); int num2; System.out.print("Enter number 2: "); do {     while (!sc.hasNextInt()) sc.next();     num2 = sc.nextInt(); } while (num2 < num1); System.out.println(num1 + " " + num2); 

You don't have to parseInt or worry about NumberFormatException. Note that since the hasNextXXX methods don't advance past any input, you may have to call next() if you want to skip past the "garbage", as shown above.

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Answer 2

1. the condition num2 < num1 should be num2 <= num1 if num2 has to be greater than num1
2. not knowing what the kb object is, I'd read a String and then trying Integer.parseInt() and if you don't catch an exception then it's a number, if you do, read a new one, maybe by setting num2 to Integer.MIN_VALUE and using the same type of logic in your example.