Error from scan nextDouble, how do I fix the problem?

Question

There is an error when I enter the double next value with a point like (1.5) I don't know why?

Even when I put (1,5) with the comma, the same result is wrong.

Can anyone help me fix it?

import java.util.Scanner;
public class ex1 {
public static void main(String[] args) {

    Scanner scan = new Scanner (System.in);

    double inch;

    System.out.println("write the distance in inch:");
    inch = scan.nextDouble();

    System.out.println("the result is " + inch * 2.54 + " cm");
}
}

the output:

write the distance in inch:
1.5
Exception in thread "main" java.util.InputMismatchException
at java.base/java.util.Scanner.throwFor(Scanner.java:943)
at java.base/java.util.Scanner.next(Scanner.java:1598)
at java.base/java.util.Scanner.nextDouble(Scanner.java:2569)
at ex1.main(ex1.java:10)

Process finished with exit code 1

What happens if you enter a number with no decimal point? `10`, for example? — Old Dog Programmer, Oct 25 '22 at 21:16
@OldDogProgrammer Without the decimal point, the program works — Kawthariiz, Oct 26 '22 at 13:37
Add this to your code: `System.out.println ( "Decimal Separator is '" + (new DecimalFormatSymbols().getDecimalSeparator()) +"'");`, and let us know the result. — Old Dog Programmer, Oct 26 '22 at 16:13
@OldDogProgrammer The code is not working because ' DecimalFormatSymbols ' It appears that there is an error. cannot find the symbol class DecimalFormatSymbol — Kawthariiz, Oct 26 '22 at 16:16
Oops. Sorry about that. Also add `import java.text.DecimalFormatSymbols;` — Old Dog Programmer, Oct 26 '22 at 16:17
@OldDogProgrammer The code is working now, but it shows the same output that I wrote in the question. The problem is not solved — Kawthariiz, Oct 26 '22 at 16:23
Strange. That's saying it should work if you use a comma as the decimal point. If you want to use a period, look at this answer: https://stackoverflow.com/questions/57924766/how-to-input-period-as-decimal-point — Old Dog Programmer, Oct 26 '22 at 16:39
@OldDogProgrammer Thank you, the program works now when I copy the decimal point that appeared in ' Decimal Separator is '٫' ' and paste it in the distance in inch the output: Decimal Separator is '٫' write the distance in inch: 1٫5 the result is 3.81 cm — Kawthariiz, Oct 26 '22 at 16:48
It looks like a comma (,) to me. But, if I copy and paste to this line `System.out.println ((',' == '٫') ? "same" : "different");`, I get "different" (The comma is to the left of `==` and the other character on the right.) — Old Dog Programmer, Oct 26 '22 at 16:54

score 0 · Answer 1 · answered Oct 26 '22 at 18:02

It looks like your computer is set to use the Arabic Decimal Separator. If you use that instead of a period (.) or comma (,), your program should work.

If you want users to be able to use a period as a decimal separator, you can add scan.useLocale(Locale.US); just after opening the Scanner

 import java.text.DecimalFormatSymbols;
 import java.util.Locale;                      
 import java.util.Scanner;

 public class ex1 {

 public static void main(String[] args) {
      Scanner scan = new Scanner(System.in);
      scan.useLocale(Locale.US);              // **** new line ****
   
      double inch;

      System.out.print("write the distance in inch: ");
      inch = scan.nextDouble();

      System.out.println("the result is " + inch * 2.54 + " cm");
   }
}

See How to input period as decimal point?

You could stick with the Arabic Decimal Separator. If you want to change it, you don't have to use Locale.US. You could use a different locale that uses a period. Or, a locale that uses a comma. Or, some other character.

Adding that line will affect only that Scanner Object. You can change it for one program by using command line options, or by adding Locale.setDefault(new Locale(~~~~)); (You have to substitute valid language, language and country, or language, country, and variant for ~~~~. You can change it for your Java installation. You can change it system wide. See How do I set the default locale in the JVM? .

Error from scan nextDouble, how do I fix the problem?

1 Answers1