Java: Changing scanner.nextDouble accepting a dot as decimal-seperator OR writing doubles with a comma in a file

File myfile = new File("Example.txt");              // the text of myFile looks like this: "3,0"
Scanner scanner1 = new Scanner(myFile);             
Double double1 = scanner1.nextDouble();             // reading "3,0" - everything okay

try (Writer filewriter = new FileWriter(myFile)) {
			filewriter.write(double1);              // writing "3.0" - inconsistent but works for me
			filewriter.flush();                     // (which obviously will not work for Java)
		} catch (IOException e1) {
			System.err.println("oops");
		}

Scanner scanner2 = new Scanner(myFile);
Double double2 = scanner2.nextDouble();             // There it is: "java.util.InputMismatchException"

My question is, how to make it write doubles with a seperation-comma in a file OR how to make scanner read doubles with a separation-dot. Both would be okay.

I already tried to use objects of DecimalFormat and so on, but it didn't change anything for me. That's why I would be very happy about some answers... Thank you for everybody trying.

To Write to the file, convert the data value to be written with a comma instead of a decimal point:

filewriter.write(String.valueOf(double1).replace(".", ","));

To Read the file and convert the data values:

// Create a File object to use in Scanner reader.
File myFile = new File("myfile.txt");
// Make sure file exists.
if (!myFile.exists()) {
throw new IllegalArgumentException("The following file path can not be found!" + 
System.lineSeparator() + myFile.getAbsolutePath());
}
// Try With Resourses used here to auto-close reader.
try (Scanner scanner2 = new Scanner(myFile)) {
// Read in each numerical token from file...
while (scanner2.hasNext()) {
// Declare a Double variable initialized to null
Double double2 = null;
/* Read in a token and remove any numerical block charaters
for example, 3.456,33 the point is common in European 
countries as a thousands separator and the comma as a 
decimal point). We also convert the comma decimal separator 
to a dot to accomodate your local and the double data type.  */
String dblStrg = scanner2.next().replaceAll("[\\.\\s']", "").replaceAll(",", ".");
/* Make sure the numerical String value is 
in fact a string representation of an 
Integer or a double data type.      */
if (dblStrg.matches("-?\\d+(\\.\\d+)?")) {
/* It is so convert the numerical value 
to a double data type.          */
double2 = Double.parseDouble(dblStrg);
}
/* If however the numerical value read from file
is not a valid Integer or double then inform
User as such.         */
if (double2 == null) {
System.out.println("Invalid Double Number! (" + dblStrg + ")");
} 
// Display the contents of the double type variable.
else {
System.out.println(double2);
}
}
}
catch (FileNotFoundException ex) {
System.err.println(ex);
}