How to read double in java from a file

Question

I'm trying to read a double from a file but I have this exception: java.util.InputMismatchException. I've tried to do the useLocale(Locale.US) but it doesn't work.

This is my code

public static void main(String[] args){
     System.out.println("Introduce the name of the file");
     Scanner teclat = new Scanner(System.in);
     teclat.useLocale(Locale.US);
     Scanner fitxer = new Scanner(new File(teclat.nextLine()));
     while(fitxer.hasNext()){
            String origen=fitxer.next();
            String desti=fitxer.next();
            double distancia=fitxer.nextDouble();
            System.out.println(origen);
            System.out.println(desti);
            System.out.println(distancia);
            ...

    }
}

Now here is the content of the file that I have to read.

city1 city2 distance(km)

string string double

Barcelona Madrid 3005.15
Barcelona Valencia 750
Los_Angeles Toronto 8026.3
......

[Chek this out](http://stackoverflow.com/questions/5769669/convert-string-to-double-in-java) — tumisma, Feb 18 '16 at 09:40

score 1 · Answer 1 · answered Feb 18 '16 at 09:40

You can like this:

String str = "Barcelona Madrid 3005.15";
double value = Double.parseDouble(str.split(" ")[2]);

Or if you want to use regex you also can do it as below:

Pattern pattern = Pattern.compile("\\d+\\.\\d+");
Matcher matcher = pattern.matcher("Barcelona Madrid 3005.15");
if (matcher.find()) {
   double value = Double.parseDouble(matcher.group());
   System.out.println("value = " + value);
}

Hope this help.

score 0 · Answer 2 · answered Feb 18 '16 at 09:46

Since you have the tuples origin, destination and distance in a single line, it is better to read the line first, and then split to words. I see in your last example that even when the name has two parts, they are written with underscores _ instead of space. So we can safely split with space.

Try with this code:

import java.io.*;

public class Test {
    public static void main(String [] args) {

        String fileName = "file.txt";

        String line = null;

        try {
            FileReader fileReader = new FileReader(fileName);

            BufferedReader bufferedReader = new BufferedReader(fileReader);

            while((line = bufferedReader.readLine()) != null) {
                String[] parts = line.split(" ");
                String origen=parts[0];
                String desti=parts[1];
                double distancia=Double.parseDouble(parts[2]);
                System.out.println(origen);
                System.out.println(desti);
                System.out.println(distancia);
            }   

            bufferedReader.close();         
        }
        catch(FileNotFoundException ex) {
            System.out.println("Unable to open file '" + fileName + "'");                
        }
        catch(IOException ex) {
            System.out.println("Error reading file '" + fileName + "'");
        }
    }
}

score 0 · Answer 3 · answered Feb 18 '16 at 09:51

You aren't setting the Locale for the second Scanner you actually read your double from.

Add this, and your code should work :

fitxer.useLocale(Locale.US);

Note that you don't need to set the Locale for the first scanner, it is only there to pass strings, not to work with double formatting.

How to read double in java from a file

3 Answers3

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