Why is java showing me exception when i am taking input from the user?

Question

public static void inputThenPrintSumAndAverage (){
        Scanner scanner = new Scanner(System.in);
        int count =0;
        int sum =0 ;
        long average = 0;
        boolean isAnInt = scanner.hasNextInt();
        while (true) {
            count++;
            int number = scanner.nextInt();
            if (isAnInt) {
                sum+=number;
                average = Math.round((sum/count));
            } else {
                break;
            }
            scanner.nextLine();
        }
        System.out.println("SUM = "+sum+ " AVG = "+average);
        scanner.close();
    }

When I am giving it a string it gives exception and doesn't even execute the "sum and avg" values. How can I change the code to make it work? If I have some wrong conceptual knowledge please help me understand the concept. Thank you.

You need to test for `.hasNextInt` ***within*** the while loop, not just before it. You need to test before getting *each* in put. You also should call `.nextLine()` *immediately* after getting the int. — Hovercraft Full Of Eels, Nov 22 '20 at 05:20

Arvind Kumar Avinash · Accepted Answer · 2020-11-22T05:36:47.720

You do not need Scanner#hasNextInt for Scanner(System.in). Also, you do not need the check, if (isAnInt). Instead, you should put a try-catch block.
You should not close Scanner(System.in); otherwise, there is no way to open it again without restarting the JVM.

Both the above thing are required when you use the Scanner for a File.

Demo:

import java.util.InputMismatchException;
import java.util.Scanner;

public class Main {
    public static void main(String[] args) {
        // Test
        inputThenPrintSumAndAverage();
    }

    public static void inputThenPrintSumAndAverage() {
        Scanner scanner = new Scanner(System.in);
        int count = 0;
        int sum = 0;
        long average = 0;
        while (true) {
            try {
                int number = scanner.nextInt();
                sum += number;
                count++;
            } catch (InputMismatchException e) {
                break;
            }
        }
        average = Math.round((sum / count));
        System.out.println("SUM = " + sum + " AVG = " + average);
    }
}

A sample run:

2
3
5
8
abc
SUM = 18 AVG = 4

Note: you can get a better precision for average if you declare it as double and store the floating-point calculation into it without rounding e.g.

import java.util.InputMismatchException;
import java.util.Scanner;

public class Main {
    public static void main(String[] args) {
        // Test
        inputThenPrintSumAndAverage();
    }

    public static void inputThenPrintSumAndAverage() {
        Scanner scanner = new Scanner(System.in);
        int count = 0;
        int sum = 0;
        double average = 0;
        while (true) {
            try {
                int number = scanner.nextInt();
                sum += number;
                count++;
            } catch (InputMismatchException e) {
                break;
            }
        }
        average = (double) sum / count;
        System.out.println("SUM = " + sum + " AVG = " + average);
    }
}

A sample run after this change:

2
3
5
8
abc
SUM = 18 AVG = 4.5

It will also be useful for you to understand this concept.

Why is java showing me exception when i am taking input from the user?

1 Answers1