Double accepted with comma instead of dot

Question

I am unable to enter doubles value in my program from my bash terminal. Below is the code I used to figure out why it is happening.

This is my code for the test:

import java.util.*;
public class DoubleTest {
    public static void main (String[] args) {
        Scanner sc = new Scanner(System.in);

        double n = sc.nextDouble();
        System.out.println(n);
    } 
}

With the following input 5, I get the expected results.

user $ java DoubleTest
   5
   5.0

Now to the interesting part. I input a Double as declared in the code, and this happens:

user $ java DoubleTest
5.0
Exception in thread "main" java.util.InputMismatchException
at java.base/java.util.Scanner.throwFor(Scanner.java:939)
at java.base/java.util.Scanner.next(Scanner.java:1594)
at java.base/java.util.Scanner.nextDouble(Scanner.java:2564)
at DoubleTest.main(DoubleTest.java:6)

And when giving a value of 5,0 - this is the result:

user $ java DoubleTest
5,0
5.0

So it seems that the . (dot) is not working, but instead , (comma) is.

I already checked my locale, but that shouldn't be the problem.

LANG="en_US.UTF-8"
LC_COLLATE="en_US.UTF-8"
LC_CTYPE="en_US.UTF-8"
LC_MESSAGES="en_US.UTF-8"
LC_MONETARY="en_US.UTF-8"
LC_NUMERIC="en_US.UTF-8"
LC_TIME="en_US.UTF-8"
LC_ALL="en_US.UTF-8"

Answer 1

Your Scanner is probably using the Denmark Locale as it uses , to format double variables instead of US default ..

Here is how you can check it (I tried locally forcing my Scanner to use Denmark Locale and it behaves the same way as in your experiments):

Scanner sc = new Scanner(System.in);
System.out.println(sc.locale().getDisplayCountry());

If this is your case, you need to set it to use the US Locale or any other you want:

Scanner sc = new Scanner(System.in);
sc.useLocale(Locale.US);
System.out.println(sc.locale().getDisplayCountry());

Alternatively, if you need to accept both , and . you could simply use a formatter. Here is one example with NumberFormat using France as Locale, which formats correctly both , and .:

NumberFormat numberFormat = NumberFormat.getInstance(Locale.FRANCE);
double doubleComma = numberFormat.parse("5,0").doubleValue();
double doubleDot = numberFormat.parse("5.0").doubleValue();

In your code you would do something like:

public static void main (String[] args) {
    try{
        Scanner sc = new Scanner(System.in);

        NumberFormat numberFormat = NumberFormat.getInstance(Locale.FRANCE);
        double n = numberFormat.parse(sc.next()).doubleValue();
        System.out.println(n);
    } catch (ParseException e) {
        e.printStackTrace();
    }
}