How to validate user input in Java?

January 17, 2022

I’m trying to get user input and check if it is "1" or "2" and display an error messages if it’s not. I keep getting error messages even when the input is correct.

Scanner user_input = new Scanner(System.in);
String choice = "";
// Input Validation
do {
   // Read user choice
   choice = user_input.nextLine();
            
   if (!choice.equals("1") || !choice.equals("2"))
      System.out.println("Invalid input. Give new value");
   }while (!choice.equals("1") || !choice.equals("2"));```

>Solution :

Your condition is incorrect.
Use logical AND if need to eliminate both 1 and 2.
I think you wanted to achieve this

       do {
            choice = user_input.nextLine();

            if (!choice.equals("1") && !choice.equals("2"))
                System.out.println("Invalid input. Give new value");
        } while (!choice.equals("1") && !choice.equals("2"));

Also to remove redundancy and improve the readability of code consider removing the validation logic to a separate method.

public static void main(String[] args) {
        Scanner user_input = new Scanner(System.in);
        String choice = "";
        
        do {
            choice = user_input.nextLine();

            if (!choice.equals("1") && !choice.equals("2"))
                System.out.println("Invalid input. Give new value");
        } while (isValid(choice));

        System.out.println("Your input is valid: " + choice);
    }
    
    private static boolean isValid(String choice) {
        return !choice.equals("1") && !choice.equals("2");
    }