User input and Exception in Java

Question

I want to add an integer to a list based on user input. The user has to type all the integers he/she wishes then press enter. if they finish inputting integer, they are supposed to press the "enter" button without typing anything.

I have made my code, but there are several mistakes

the exception keeps popping up because every time say for example I enter integer 10, then I finish. I press "enter" with nothing. this raises the exception. how do I tackle this problem?

and another thing, how do I make the program so that if the user puts invalid input, instead of crashing or breaking. It asks the user again to prompt the correct input.

this is what I have done

package basic.functions;
import java.util.*;
import java.text.DecimalFormat;

public class Percent {
    public static void main(String[] args) {
        Scanner reader = new Scanner(System.in);
        reader.useDelimiter(System.getProperty("line.separator"));
        List<Integer> list = new ArrayList<>();
        System.out.println("Enter Integer: ");

        while (true) {
            try {
                int n = reader.nextInt();
                list.add(Integer.valueOf(n));
            } catch (InputMismatchException exception) {
                System.out.println("Not an integer, please try again");
                break;

            }
        }
        reader.close();
   }
}

output

Enter Integer: 
10

Not an integer, please try again 
[10]

This is a definite duplicate of stackoverflow.com/questions/43760671/…, asked by the same user. — Kallaste
– Kallaste, Commented Oct 6, 2022 at 1:08

Ousmane D. · Accepted Answer · 2017-05-03 16:05:39Z

1

I'd suggest you utilise Scanner#hasNextInt to identify whether an integer has been entered or not. As for when the "user presses enter without typing anything", we can simply use the String#isEmpty method.

while (true) {
     if(reader.hasNextInt()) list.add(reader.nextInt());
     else if(reader.hasNext() && reader.next().isEmpty()) break;
     else System.out.println("please enter an integer value");
}

note - in this case, you don't need to catch InputMismatchException because it won't be thrown.

edited May 3, 2017 at 16:05

answered May 3, 2017 at 14:33

Ousmane D.

56.6k8 gold badges101 silver badges134 bronze badges

Sign up to request clarification or add additional context in comments.

3 Comments

Kutam Over a year ago

I think youve mistaken what I mean. Its not the user typing enter. its if the user press enter without putting any input. then stop

Kutam Over a year ago

thanks, this is what I had at the start, but some guy told me to change it. the guy in the bottom. Because i want to throw exception. the idea is so that if user enter invalid input, there will be an error message, asking the user to re prompt.

Ousmane D. Over a year ago

@Kutam see my update which notifies the user to enter correct data when he/she has not. Also, because the Scanner has methods that help you know whether what is entered is an int, double, string etc, we don't need to concern ourselves with try/catch and that makes your code looks messy. This is a simple task and should be accomplished just using the methods of the Scanner.

Tim B · Accepted Answer · 2017-05-03 14:32:56Z

-1

while (true) is generally a bad sign, if you ever have that in your code you are almost certainly wrong.

What you probably want is something like this:

String input;
do {
  input = reader.next();
  // Parse the input to an integer using Integer.valueOf()
  // Add it to the list if it succeeds
  // You will need your try/catch etc here
while (!input.isEmpty());

Here the loop is checking the exit condition and running until it meets it. Your processing is still done inside the loop as normal but the program flow is a lot cleaner.

answered May 3, 2017 at 14:32

Tim B

41.3k16 gold badges87 silver badges132 bronze badges

Collectives™ on Stack Overflow

User input and Exception in Java

2 Answers 2

3 Comments

Comments

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

3 Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Linked

Related