How to properly use a try/catch block in a while loop to handle invalid input in Java?

I’m trying to write a Java program that asks the user to input a positive integer inside a while loop. The loop should continue until valid input is provided.

I’ve tried using a try/catch block to handle invalid inputs like strings, but I’m still running into issues. For example:

• When the user enters a string, the program throws an InputMismatchException and skips re-prompting the user.

• I tried adding scanner.nextLine() to clear the input buffer, but it didn’t work as expected.

Here’s the code I’ve written so far:

import java.util.Scanner;

public class InputExample {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        int userInput = -1;

        while (userInput < 0) {
            try {
                System.out.print("Enter a positive number: ");
                userInput = scanner.nextInt(); // Crashes if invalid input is entered
            } catch (InputMismatchException e) {
                System.out.println("Invalid input. Please enter a valid number.");
                scanner.nextLine(); // Attempt to clear the buffer, but it doesn't work
            }
        }

        System.out.println("You entered: " + userInput);
        scanner.close();
    }
}

The issue:

1. When invalid input (like a string) is entered, the program skips re-prompting the user.

2. I suspect there’s an issue with how I’m clearing the input buffer using scanner.nextLine().

What I’ve tried:

1. Wrapping the scanner.nextInt() inside a try/catch block to catch the exception.

2. Using scanner.nextLine() after catching the exception to clear the input.

My question:

How can I properly handle invalid input in this scenario so that the program keeps re-prompting the user until a valid positive integer is provided?

Perhaps try something like:

String userInput = "";

while (true) {  // loop until valid input 
  userInput = scanner.nextLine();
  if (isInteger(userInput)) 
    break;
  System.out.print("Please enter a valid number.");
}
  
private static boolean isInteger(String str) {
  try {
    Integer.parseInt(str); 
    return true;
  } catch(NumberFormatException e) {
    return false;
  }

These previous answers may also help: https://stackoverflow.com/a/53904761/6423542 https://stackoverflow.com/a/24836513/6423542