How to Robustly Parse Doubles with Comma as Decimal Separator in Java?

Parsing Double with Comma as Decimal Separator: A Comprehensive Solution

When working with data that uses comma (,) as the decimal separator, parsing it into a double using Double.valueOf() can result in a NumberFormatException. This is because Double.valueOf() expects a period (.) as the decimal separator.

One solution is to replace the comma with a period using String.replaceAll(), as shown in the question. However, there is a more robust and locale-aware approach using java.text.NumberFormat.

Leveraging NumberFormat for Locale-Specific Parsing

NumberFormat provides methods to parse and format numbers according to the specified locale. To parse a string with a comma as the decimal separator, use the following steps:

1. Create a NumberFormat instance using NumberFormat.getInstance(Locale.FRANCE) or NumberFormat.getInstance(Locale.getDefault()) to support multi-language apps.
2. Call format.parse(String) to parse the string into a Number object.
3. Convert the Number object to a double using number.doubleValue().

Here's the code demonstrating this approach:

NumberFormat format = NumberFormat.getInstance(Locale.FRANCE);
Number number = format.parse("1,234");
double d = number.doubleValue();

System.out.println(d); // Prints 1.234

By using NumberFormat, you can parse double values with commas as decimal separators in a locale-specific manner, ensuring accurate results even in globalized applications.

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