用逗号代替点接受双重

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();
    }
}