如何在 Java 中验证用户输入

Question

I am currently experimenting with Java, trying to get the user to input an integer. If the user doesn't enter an integer I want a message to appear saying "You need to enter an Integer: " with a completely new input field to the original one.

Code:

import java.util.Scanner;

public class Test {

    public static void main(String[] args) {
    
        Scanner inputScanner = new Scanner(System.in);
        
        int counter = 0;
    
        boolean run = true;
        
        int userInput = 0;
        
        while (run) {
        
            System.out.print("Enter an integer: ");
            
            if (inputScanner.hasNextInt()) {
            
                userInput = inputScanner.nextInt();
            
            } else if (!inputScanner.hasNextInt()) {
                while (!inputScanner.hasNextInt()) {
                
                    System.out.print("You need to enter an Integer: ");
                    userInput = inputScanner.nextInt();
                
                }
            
            }
            
            System.out.println(userInput);
            
            if (counter == 6) {
            
                run = false;
            
            }
            counter++;
        
        }
    
    }

}

At the moment the code above gives an Exception error ("java.util.InputMismatchException"). I have tried to use a try/catch but this doesn't really work because I want the user to see the second message ("You need to enter an Integer") everytime they don't enter an integer and I don't want it to re-loop around the main run loop for the same reason. I'm sure there is a better way to do this, however I am not sure of it. Any help will be massively appreciated, thanks in advance.

Answer 1

In this case it would make more sense for the Scanner to use hasNextLine and then convert the String to an Integer. If that you could do something like this:

try {
   new Integer(inputScanner.hasNextLine);
} catch (Exception e) {
    System.out.println(“<error message>”)
}

In place of the if(inputScanner.hasNextInt()) due to the fact that the hasNextInt function will error out if there is not an Integer to be read.