How can I find out which (wrong) data type the user inputted instead of an int?

Question

So I'm completely new to Java and programming in general and I'm doing my first little program where I ask the user's age and determine whether they're an adult. I wanted to add an error message which tells the user they inputted the wrong data type and not an integer. However, when I write a string as input, it displays the error message, but it only says Integer and not String.

import java.util.Scanner;

public class Main {
    public static void main(String[] args) {
        //create scanner object
        Scanner sc = new Scanner(System.in);

        System.out.println("What is your age?"); //ask for input
        int age = 0;
        try { //record input and check value
            age = sc.nextInt();
            if (age >= 18) {
                System.out.println("You are an adult.");
            } else {
                System.out.println("You are not an adult.");
            }
        } catch (Exception e) { //find out which wrong type the user inputted and tell it to them
            System.out.println("Error: you did not input a full number, instead you wrote a "+((Object) age).getClass().getSimpleName());
        }

    }
}

As I said, I expect it to say that I wrote a string and not an integer, but for some reason it still says it's an Integer. How can I fix that?

So here is the input window:

What is your age? test Error: you did not input a full number, instead you wrote a Integer

Process finished with exit code 0

I suggest you change the print to this: System.out.println("Error "+e+": you did not input a full number, instead you wrote a "+((Object) age).getClass().getSimpleName());. The reason is, once the scanner scans an integer, via sc.nextInt(), you can't get anything but an integer there. HOWEVER, if i enter "asdfg", the scanner might fail to parse asdfg into an integer, throwing an exception. Remember, everything the user inputs is a String, and then you try to parse it into a whatever, so stating "you entered string instead of int" is a useless and senseless print imho. — Shark
– Shark, Commented Dec 30, 2022 at 12:23

Hashila · Accepted Answer · 2022-12-30 12:31:45Z

2

You can get values from scanner as Strings by it self and then convert it to the int type:

Scanner sc = new Scanner(System.in);

    System.out.println("What is your age?"); //ask for input
    Object age = 0;
    try { //record input and check value
        age = sc.next();
        int intAge = Integer.parseInt((String) age);
        if (intAge >= 18) {
            System.out.println("You are an adult.");
        } else {
            System.out.println("You are not an adult.");
        }
    } catch (NumberFormatException e) { //find out which wrong type the user inputted and tell it to them
        System.out.println("Error: you did not input a full number, instead you wrote a "+ age.getClass().getSimpleName());
    }

I recommend you to use correct exception types when you are handling exceptions, thanks

edited Dec 30, 2022 at 12:31

answered Dec 30, 2022 at 12:29

Hashila

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1 Comment

fedyafrench Over a year ago

Thanks! This worked! Also I'll be sure to try and use correct exceptions in the future.

Sriram · Accepted Answer · 2022-12-30 12:24:27Z

1

This is expected behavior because you have declared age is int. It wont consider the datatype you gave as input but in which the variable is declared.

answered Dec 30, 2022 at 12:24

Sriram

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