How to Gracefully Handle Invalid Integer Input with Java's Scanner?

How to Handle Invalid Input Using Scanner

While using Scanner for user input, handling invalid input, such as non-numerical characters, is crucial for program robustness. Let's explore a solution to handle this issue.

Consider the following code snippet:

Scanner kb = new Scanner(System.in);
int num1;
int num2 = 0;

System.out.print("Enter number 1: ");
num1 = kb.nextInt();

while (num2 <p>This code aims to obtain two integers from the user, ensuring that the second number (num2) is greater than the first (num1). However, it has two limitations:</p><ol>
<li>It doesn't check for non-numerical input, causing the program to crash if the user enters a character instead of a number.</li>
<li>The loop continues even after valid input is entered for num2 because the while condition is always true.</li>
</ol><p>To address these issues, we can leverage the Scanner.hasNextInt() method, which determines if the next token in the input can be interpreted as an integer.</p><p>The following code snippet incorporates these improvements:</p><pre class="brush:php;toolbar:false">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 <p>By checking for valid input using hasNextInt() and ignoring invalid characters, the program handles non-numerical input gracefully. Additionally, the do-while loop ensures that the second number is greater than the first, preventing the loop from continuing after valid input is obtained.</p>

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