How Can I Robustly Handle Invalid Integer Input with Java's Scanner?

Overcoming Scanner Invalid Input Limitations

In an attempt to enhance program robustness, users face challenges in restricting input to valid integer values and handling non-numeric entries. A popular library, Scanner, offers a solution to these hurdles.

Validating Integer Input

Scanner provides the hasNextInt() method, which verifies if the upcoming input can be interpreted as an integer. This method remains static, implying it doesn't advance past any input.

Example Implementation

Incorporating hasNextInt() allows for an elegant solution:

Scanner sc = new Scanner(System.in);
System.out.print("Enter number 1: ");
while (!sc.hasNextInt()) sc.next(); // Skips non-numeric input
int num1 = sc.nextInt();
int num2;
System.out.print("Enter number 2: ");
do {
    while (!sc.hasNextInt()) sc.next(); // Skips non-numeric input
    num2 = sc.nextInt();
} while (num2 < num1); // Enforces num2 being greater than num1

Exceptional Input Handling

Since hasNextXXX methods stay static, it's necessary to call next() to discard any "garbage" from invalid input.

Related Questions

• [How do I prevent Scanner from raising exceptions for incorrect input types?](https://java.stackexchange.com/questions/2600398/how-do-i-keep-a-scanner-from-throwing-exceptions-when-the-wrong-type-is-entered)

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